LECTURE S Microbial Growth - PowerPoint Presentation

1. LECTURESMicrobial Growth Kinetics

2. Growth CurveLog CFU/mlOptical DensityLag

3. First Order KineticsFood microbiology is concerned with all phasesOf microbial growth (lag,log, stationary, death phase).Growth curves are normally plotted as the number of cells on a log scale or log10 cell number versus time.

4. One generation

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6. Growth Terminology and the concept of exponential growthThe interval for the formation of two cells from one is called a generation The time required for this to occur is called the generation time. Generation time is the time required for the cell population to double (the cell mass doubles during this period as well). Because of this, the generation time is also called the doubling time.

7. In nature, microbial doubling times may be much longer than those obtained in laboratory culture. This is because in nature, ideal growth conditions for a given organism may exist only intermittently. Depending on resource availability, physiochemical conditions (temperature, pH, and the like), moisture availability, and seasonal changes, bacterial populations in nature double only once every few weeks, or even longer.

8. A mathematical relationship exists between the number of cells present in a culture initially and the number present after a period of exponential growth: N = N02n where N is the final cell number, No is the initial cell number, n is the number of generations that have occurred during the period of exponential growth.

9. The Mathematics of Exponential Growth As one cell divides to become two cells, 2° --'> 21. As two cells become four, 21 --'> 22, and so on

10. The generation time (g) of the exponentially growing population is (t / n), where t is the duration of exponential growth expressed in days, hours, or minutes, depending on the organism and the growth conditions. From a knowledge of the initial and final cell numbers in an exponentially growing cell population, it is possible to calculate n, and from n and knowledge of t, the generation time g.

11. Relation equation of N and No to nThe equation N = No2n can be expressed in terms of n as follows: N = No2n log N = log No + n log 2 log N – log No = n log 2n = log N – log No = log N – log No log 2 0.301 = 3.3 (log N – log No)

12. exampleN = 108, No = 5 X 107, and t = 2 n = 3.3 (log N – log No) n = 3.3 [log(108) - log(5 X 107)] = 3.3(8 - 7.69) = 3.3(0.301) = 1 generation time, g = t/n = 2 / 1 = 2 h

13. Related growth parameterThe generation time g of an exponentially growing culture can also be calculated from the slope of the line obtained in the semilogarithmic plot of exponential growth. The slope is equal to 0.301 n/t (log 2n/t) and in the above example would be 0.301(1)/2, or 0.15. Since g is equal 0.301/slope, we arrive at the same value of 2 for g. The term 0.301nlt is called the specific growth rate, abbreviated k.

14. The Growth cycle or phases of microbial growthobserved when microorganisms are cultivated in batch cultureculture incubated in a closed vessel with a single batch of mediumusually plotted as logarithm of cell number versus timeusually has four distinct phases

15. Table First order kinetics to describe exponential growth and inactivationGrowth2Irradiation1a. N=N0eµt1b. N=N0eN=N0e-Dd/D02a. 2.3 log(N/N0)=µt2b. 2.3 log(N/N0)=-kt3a.∆t=2.3 log(N/N0)/µ3b. ∆t=-2.3 log(N/N0)/k4.a. g=0.693/µ4b. D=2.3/k5b. Ea=Growth2Irradiation1a. N=N0eµtN=N0e-Dd/D02a. 2.3 log(N/N0)=µt2b. 2.3 log(N/N0)=-kt3a.∆t=2.3 log(N/N0)/µ3b. ∆t=-2.3 log(N/N0)/k4.a. g=0.693/µ4b. D=2.3/kN=Final cell number(CFU/ml)N0=Initial cell number t=time (h)µ=Specific growth rate (h-1)g=Doubling time(generation time)(h)k=rate constant (h-1)D=Decimal reduction time(h)Ea=Activation energy(kcal/mol)T1 and T2,reference and test temperature(K)D0=Rate constant (h-1)Dd=Dose(Gy)

16. The rate of growth is directly proportional to cell concentration or biomass- i.e. dx/dt α X dx/dt = μX ----------1 Where, X is the concentration of microbial biomass, t is time, in hours μ is the specific growth rate, in hours -1

17. On integration of equation (1) from t=0 to t=t ,we have: xt = xo e μt --------- 2Where,Xo is the original biomass concentration,Xt is the biomass concentration after the time interval, t hours,e is the base of the natural logarithm.

18. On taking natural logarithms of equation (2) we have : In Xt = In Xo + μt (3)

19. Therefore, a plot of the natural logarithm of biomass concentration against time should yield a straight line, the slope of which would equal to μ. During the exponential phase nutrients are in excess and the organism is growing at its maximum specific growth rate, ‘μmax ‘ for the prevailing conditions.

20. Typical values of μmax for a range of microorganisms are given below in the Table.

21. Three causes for lag: physiological lag low initial numbersLag phaseappropriate gene(s) absentgrowth approx. = 0 (dX/dt = 0)

22. Nutrients and conditions are not limiting Exponential phase20212223242n20212223242n20212223242n20212223242n20212223242n20212223242ngrowth = 2n or X = 2nX0Where X0 = initial number of cells X = final number of cells n = number of generations

23. Cells grown on salicylate, 0.1%Example: An experiment was performed in a lab flask growing cells on 0.1% salicylate and starting with 2.2 x 104 cells. As the experiment below shows, at the end there were 3.8 x 109 cells.3.8 x 109 = 2n(2.2 x 104)1.73 x 105 = 2nlog(1.73 x 105) = nlog217.4 = nThis is an increase is 5 orders of magnitude!!How many doublings or generations occurred? X = 2nX0

24. dX/dt = uX where u = specific growth rate (h-1)Rearrange: dX/X = udtIntegrate: lnX = ut + C, where C = lnX0 lnX = ut + ln X0 or X = X0eut Note that u, the growth rate, is the slope of this straight liney = mx + b (equation for a straight line)dX/dt = uX where u = specific growth rate (h-1)Calculating growth rate during exponential growth

25. Rearrange: dX/X = udtIntegrate: lnX = ut + C, where C = lnX0 lnX = ut + ln X0 or X = X0eut Note that u, the growth rate, is the slope of this straight liney = mx + b (equation for a straight line)Calculating growth rate during exponential growthdX/dt = uX where u = specific growth rate (h-1)

26. lnX = ut + ln X0 or u = lnX – lnX0 t – t0u = ln 5.5 x 108 – ln 1.7 x 105 8.2 - 4.2= 2 hr-1Find the slope of this growth curve

27. Growth Kineticsg can be calculated by g==Example: Initial population is 103 CFU/ml and increased to 106 cells in 300 min. What is generation time?g==30 min or you can first calculate µ and then calculate g.2.3log(N/N0)= µ t µ =0.023min-1 and g=0.693/ µ g=30.13 min µ can be obtained by slope of straight line when the log numbers of the cell is plotted against time. 

28. Ex:Ground meat manufactured with N0=1.2*104 CFU/g.How long it be held at 7°C before reaching a level of 108CFU/g (for µ=0.025 h-1)N=N0eµt108 =1.2*104e0.025tt=361.12 h

29. Time(h)Viable organism amount (N)010321.5*10341.7*1038104162*105243.5 108302.7*108For given information below for Lactobacillus growth at 37 °C.a)Plot Growth curve and Show main growth phases.b)Calculate specific growth rate (µ)c)Calculate generation time.d)If you incubate this bacteria at20 °C, what kind of things or changes expected in the results?

30. Plotting growth curveTimeCFU/mlln(CFU/ml)010006,91215007,31417007,448100009,211620000012,212435000000019,673027000000019,41Time periods0-4 hours- lag phase4- 24 hours-log phase24-30 hours-stationary phase

31. Growth phasesTime periods0-4 hours- lag phase4- 24 hours-log phase24-30 hours-stationary phaseIn Xt = In Xo + μt can be used for between 4 and 24 hours

32. In Xt = In Xo + μtfrom straight lineequationμ=0,5933h-1orIn Xt = In Xo + μtln 3.5 108=ln1.7*103+ μ(20) μ=0,61 h-1g=ln2/ μ0,69/0,59=1,17hours

33. Death Kinetics-Killing can be by heat, radiation, acid, bacteriocin and other lethal agents is also governed by first order kinetics.D value=amount of time required to reduce N0 by 90% is the most frequently used constant.The relationship between k and temperature is explained by arrhenius equationk=A eEa/RT

34. Z valueZ value= a number of degrees required to change in the D values by a factor 10, or It is the temperature required for one log10 reduction in the D-value.

35. z-value is used to determine the time values with different D-values at different temperatures with its equation shown below:where T is temperature in °F or °C.This D-value is affected by pH of the product where low pH has faster D values on various foods. The D-value at an unknown temperature can be calculated knowing the D-value at a given temperature provided the Z-value is known.

36. For example: If D vaue at 121 °C is 1.5 min and z value is 10 °C. The D value at 131 °C will be 0.15 min.Example: if it takes an increase of 10°F to move the curve one log, then our z-value is 10. Given a D-value of 4.5 minutes at 150°F, the D-value can be calculated for 160°F by reducing the time by 1 log. The new D-value for 160°F given the z-value is 0.45 minutes. This means that each 10°F increase in temperature will reduce our D-value by 1 log. Conversely, a 10°F decrease in temperature will increase our D-value by 1 log. So, the D-value for a temperature of 140°F would be 45 minutes.

37. Microbial Growth Characteristics in Foods1.Competition 2.Metabiotic Growth3.Symbiotic Growth4.Synergistic Growth5.Commensalism6.Antagonistic Growth7.Predation

38. 1.Competition Energy and nutrient sources are often present in limiting concentrations; microorganisms compete each other for nutrients and results in exclusion of slower growing species.Foods contain a mixed population of microorganisms. Competition among the different kinds of microorganisms in food determines which one will outgrow the others and cause its characteristics types of changes.

39. 2. Metabiotic (Sequential)GrowthDifferent types of microorganism present normally in foods, but the predominant types can change with time during storage.Ex: If the food is packaged in a bag with a little bit of air(e.g. ground meat),the aerobes will grow first and utilize O2. The environment will become anaerobic, in which anaerobes grow favorably.Ex: In most food fermentations metabiotic growth is observed.In Sauerkraut fermentation,4 different bacterial species grow in succession, one creating the favorable conditions for the next one.First ,coliform grow produce acid and activate the growth of lactic acid bacteria.second, Leuconoctoc mesenteroides ; third Lb. plantarumLast, acid tolerant Lb. brevis

40. 3.Symbiotic GrowthTwo or more microorganisms help one another during growth in food.In yogurt; there are two types of lactic acid bacteria.1. S. thermophilus2.Lb. bulgaricusS. thermophilus produces small quantities of formic acid and stimulates Lb. bulgaricus.Lb. bulgaricus produce aminoacid inturn these products stimulate the growth Str. thermophilus

41. 4.Synergistic GrowthWhen two types of microorganism grow together and may able to bring changes which could not produce alone.Acetaldehyde is desirable flavor component in yogurt.S. thermophilus produce 8 ppm Acetaldehyde Lb. bulgaricus produce 10 ppm Acetaldehyde in milk independently,when they grow together, they produce 30ppm Acetaldehyde .

42. 5.CommensalismMicroorganisms may not effect each other but one organisms uses the substrate whic is produced by other.For ex: cellulose hydrolyzing microorganisms produce glucose and cellulose non hydrolyzing micoorganims use this glucose.One population benefits while latter remain unaffected.

43. 6.Antagonistic GrowthMicroorganisms can adversely affect each other, one kill the other. Some Gr(+) bacteria produce antimicrobial components that can kill many other types.For ex: L. lactis ssp. lactis produce bacteriocin called nisin and inhibits Gr(-)bacteria. 6.Predation GrowthThe example for predatory growth is the attachment of bacteria of the genus Bdellovibrio, Daptobacter and Stenotrphomonas maltophilia to Gr(-) bacteria,penetrating the cell wall, and subsequently multipying witin the periplasmic space.

44. III. Chemical Changes Caused my microorganismsChanges in nitrogenous organic compoundsChanges in organic carbon compoundsa) Carbohydratesb)Organic acidsc)Other compoundsd)Lipidse)Pectic substances

45. FE206- Food MicrobiologySpring 2018LECTURES PRINCIPLES OF FOOD SPOİLAGE

46. outlineI.Introductionii. Food Spoilage A. Classification of foods depending on stability B.Potentially hazard foods C. Types of agents causing food spoilage D. Microbial Food Spoilage E. Nonmicrobial Food spoilage Chemical Spoilage Non enzymatic food Spoilage F. Practices to prevent Food spoilage

47. Introduction for Principles of Food SpoilageMicrobial growth can result with microbial food spoilage, desirable products or release of extracellular and intracellular enzymes. Spoilage can also occur due to action of microbial enzymes in the absence of the viable cells. Spoilage of different types of foods results with changes in color, odor, and texture, formation of slime, accumulation of gas and release of liquid(exudates, purge)

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50. Food SpoilageSpoilage: Decay or decomposition of food which is not accepted by consumer. The criteria for acceptability of foods are;1.the desired stage of maturity2.Freedom from pollution3.Freedom from objectionable biological, chemical and physical changes resulting from action of food enzymes; activity of microbes, insets and rodents, invasion of parasites, damages.4.Freedom from m.o’s and parasites causing foodborne illnesses.

51. Classification of Foods Depending on Stability1. Highly perishable foods;If no preservation is applied, the quality retentian time is about 1-3 days. It incudes meat, poultry,fish,raw milk,eggs, many fruits and vegetables and all cooked foods except the dry and very acid ones.2.Semiperishable foods;Lighty processed lsuch as pasteurization of milk and egg products and refrigerated. the quality retention time is about 1-3 weeks.Other examples frozen foods, baked goods, hard cheeses and fruits.3.Semishelfstable foods;Two or more preservation process can be used (the hurdle concept) such as vacuum packaging the cooked meat products, the quality retention time is about 1-4 months.4.Shelf stable foods(nonperishable foods)Highly processed (such as heat processed, sterilizes and hermetically sealed)such as vegetable , dried milk products with a qualty retention up to 1 year or more .Other examples are sugar, flour,dry foods, etc.

52. Potentially Hazard foodsThe following is the definition used in the FDA Food (a) "Potentially hazardous food" means a food that is natural or synthetic and that requires temperature control because it is in a form capable of supporting:(i) The rapid and progressive growth of infectious or toxigenic microorganisms;(ii) The growth and toxin production of Clostridium botulinum,; or(iii) In raw shell eggs, the growth of Salmonella enteritidis(b) "Potentially hazardous food" includes an animal food (a food of animal origin) that is raw or heat-treated; a food of plant origin that is heat-treated or consists of raw seed sprouts; cut melons; and garlic-in-oil mixtures.

53. Potentially Hazard foods(c) "Potentially hazardous food" does not include:(i) An air-cooled hard-boiled egg with shell intact;(ii) A food with an aw value of 0.85 or less;(iii) A food with a pH level of 4.6 or below when measured at 24 °C (75 °F);(iv) A food, in an unopened hermetically sealed container, that is commercially processed to achieve and maintain commercial sterility under conditions of non refrigerated storage and distribution; and(v) A food for which laboratory evidence demonstrates that the rapid and progressive growth of infectious or toxigenic microorganisms or the growth of S. enteritidis in eggs or C. botulinum can not occur, such as a food that has an aw and a pH that are above the levels specified under Subparagraphs (c)(ii) and (iii) of this definition and that may contain a preservative, other barrier to the growth of microorganisms, or a combination of barriers that inhibit the growth of microorganisms.(vi) A food that does not support the growth of microorganisms as specified under Subparagraph (a) of this definition even though the food may contain an infectious or toxigenic microorganism or chemical or physical contaminant at a level sufficient to cause illness

54. Types of Agents Causing Food SpoilageGrowth activity of m.o’s2.Insects,rodents and animals3.Action of enzymes4.Purely chemical reactions in the food such as oxidation and browning5.Physical changes caused by freezing,burning, drying, pressure, etc.6. Presence of foreign material in the food such as heavy metals, toxins, non food materials and etc.7.Presence of parasites or their eggs.

55. Microbial Food SpoilageMicrobial spoilage occurs as a result of microbial contamination with foods and activities of microorganisms under suitable conditionsFactors Effecting Food Spoilage a)Kinds and numbers of m.o’s in food b)Food residues c)Moisture content d)Time e)Temperature f)Physical state and structure of Food g)Significance of microbia types

56. 2. Metabolism of Food nutrients and Chemical Changesa)Metabolism of nitrogenous compoundB) Metabolism of non-nitrogenous compoundsCarbohydratesOrganic AcidsLipidsPectic substancesOther compounds

57. Metabolism of Food nutrients and Chemical Changesa)Metabolism of nitrogenous compoundsThe nitrogen in foods is present in the form of proteins. Microbial extracellular proteinases hydrolyze proteins to polypeptide, simpler peptides and amino acids. Peptide give a bitter taste. catalysis the hydrolysis of polypeptides to simpler peptides and aminoacids. They can give desirable or undesirable flavor.Decomposition of proteins or aminoacids may result in the production of odors and is callded putrefaction.It results in foul-smelling,sulfur-containing products.These are hydrogen, methy and ethyl sulfides, mercaptan, ammonia,amines,indole and others.

58. a)Metabolism of non-nitrogenous compoundmo’s use carbohydates to obtain energy. Organic acids,aldehydes,ketones,alcolhols,glycosides,cyclic compounds and lipids are also used as carbon and energy sources.Carbohydrates: polysaccharides are hydrolyzed by extracellular enzymes and simple sugars are used. Glucose can be decomposed in 6 main fermentation.1)alcolholic ferm 2)Simple lactic ferm. 3)a mixed lactic ferm(heteroferm.) 4)coliform type ferm. 5)the propionic ferm 6)butyric-isopropyl ferm

59. a)Metabolism of non-nitrogenous compoundOrganic acids; m.o’ oxidase organic acids to carbohydrates and medium become more alkaline. Some mo’s can oxidase organic acids to CO2 and water such as yeast(film on pickle)Lipids; Fats hydrolyzed to glycerol and fatty acids. Phospholipids can degraded to phosphate, glycerol, fatty acids, nitrogenous base. Lipoproteins can be hydrolyzed to proteins, cholesterol ester and phospholipids.Other compounds; alcohols are oxidized to organic acids acetaldeydes may be oxidized to acetic acid or ethanol.

60. Preference for metabolismmo’ use carbohydrates first, fallowed by NPN (non protein nitrogeneus compounds )and proteinaceous compounds and lipids.Small nutrient molecules are used before the large molecules. (For ex: yeast growing in fruit juice cam metabolize simple carboydrates such us fructose, glucose and sucrose)Type of nutrients can effect types of spoilage in foods. For ex: meats with low level of carbohydrates are spoiled by putrefactive m.o’s.

61. E)Nonmicrobial Food Spoilage1.Chemical spoilage-The Maillard reaction  occurs between a carbonyl compound like a reducing sugar, and an amine, like an amino acid, peptide, or protein.-lipid oxidationExamples: repetitive usage of frying oils in restaurants, odor becomes heavy.Discoloration of surface of red meat is caused by non enzymatic reactions, oxidation of myoglobin to metmygoglobin

62. Nonmicrobial Food Spoilage2. Enzymatic spoilageThe enzymes on banana cause maturation and color changesRipening and softening fruitsBacteria also produce enzymesEnzymes in vegetable can be inactivated by blanching or their activities can be decreased at cold temperatures below 4 ˚C.

63. F)Practices to prevent Food SpoilagePackage the fresh productUse the best packaging material for length of time the food remains in the market channel.Use good sanitation and personal hygiene habits during processing and packaging of food.Use sanitation habits for equipment used in the food production.Cool processed foods as quickly as possible to below 4 ˚C.Keep left over foods covered to prevent contamination and put them under refrigeration as soon as possible.Keep hot food on steam table above 60 ˚ C .Cool the foods in large containerrs containing ice.Cook food up to an internal temperature of 75 ˚ C to destroy both enzymes and vegetative bacterial cells.Type of packaging material should be considered carefully to control food spoilage.

64. FE206Food MicrobiologyFall 2016LECTURE SPOILAGE OF MILK AND DAIRY PRODUCTS

65. Composition of MilkThe main components are water, lactose, casein, fat,minerals and non protein nitrogenous compounds(Table )Heat treatments affect microbial growth by increasing available nitrogen thought protein hydrolysis and by inhibiting sulfhydryl compounds

66. ComponentAmount(g/L)ComponentamountWater 0.87Magnesium0.12Lactose0.48Citrate1.76Fat0.37Chloride1.04Casein0.26Phosphorus0.74Whey Protein0.006Nonprotein nitrogen(NPN)(mg/ml)Minerals (mg/ml)Total NPN0.30Sodium0.58Urea N0.14Potassium1.40Peptide N0.03Calcium1.18Aminoacid N0.04Creatine N0.02Table.approximate Concentrations of some nutritional components of milk

67. SpoilageActually initial milk contains relatively few bacteria when it leave s the udder.Contamination can comes from, Animal, manure, air, utensils,worker, milking machines.Undesirable bacteria from these sources are lactic streptecocci,coliform, psychrotrophic Gram-negative rods,thermodurics(e.g. Micrococci,enterococci,bacilli) and brevibacteria.Proper sanitizing and cleaning reduce contamination.Quaternary ammonium compounds-reducing Gram positives but tend to increase Gram negative rodsHyphochlorides-favor Gram positive bacteria(micrococci and bacilli)Filling equipments are most often the source of psychrotrophs.Fresh, nonpasteruired milk contains varying numbers of m.o’s depending on milking,cleaning and handling of utensils.

68. Sources of contamination 1)On the FarmMilk contains relatively few bacteria when it leaves the udder of the healthy cow and generally these bacteria do not grow in milk.During milking, the contamination of milk is by the exterior of the udder and adjacent areas. Bacteria found in the manure, soil and water may enter from this source.

69. Two most significant sources of contamination are dairy utensils and milk-contact surface, including the milk pail or milking machines.Undesirable bacteria from these sources include lactic streptococci, coliform bacteria, psychrotrophic gram-negative rods, and thermodurics, those which survive pasteurization, e.g., micrococci, enterococci, bacilli, and brevibacteria.

70. Other possible sources of contamination are the hands and arms of the milker or dairy workers, the air of the barn or milking parlor, and flies.The number of bacteria per milliliter of milk added from various sources depends on the care taken to avoid contamination.

71. 2)In Transit and at Manufacturing LevelAfter milk is left in the farm, the possible contamination include the tanker truck, transfer pipes, sampling utensils, and the equipment at the market-milk plant or other processing plant.Pipelines, vats, tanks pumps, valves, separators are the possible sources of bacteria.The amount or level of contamination from each of these sources depends on cleaning and sanitizing methods.Hands and arms of the employees are a possible source of contamination and pathogens.

72. Raw milk at refrigerated temperatures for several daysPsycrotrophic strains of bacterial generaAerococcusBacillusLactobacillusLeuconostocMicrobacteriumMicrococcusPropionibacteriumProteusPseudomonasStreptococcusColiforms and othersPasteurization eliminates all but thermodurics such as Bacillus, Clostridium,Lactobacillus and streptococcus may survive

73. B)Spoilage in MilkLactose-the m.o’s lactose hydrolyzing enzymesMilk fat-be hydrolyzed by microbial lipases to produce small molecular volatile fatty acids(butryric,capric, and caporic acid)Pasteurized milk is expected to shelf life of 14-20 days at 4 ˚C.Some defects of fluid milk that result from bacterial growth can be seen in Table 5.2

74. 1.RawmilkMilk is excellent medium for m.o’s due to high moisture, nearly neutral pH and rich in nutrients.Primary spoilage bacteria are aerobic Gram negative psychrotrophic rods, such as alcaligenes,flavobacterium,pseudomanas and some coliforms.Psychrotrophic spoilage microflora in milk is generally proteolytic,lipolytic and phospholipolitic Pseudomonas ssp (P. fluorescens, P. fragi,P. putida, and P. lundensis) growing at 3-7 ˚C.Their generation times in milk are short and cause spoilage within 5 days if initial contains 1 cell/ml.Pseudomonas ssp Can not hydrolyze lactose, can proteolysis and produce bitter, fruity, putrid or unclean flavor and coagulate milk. Rancid and fruit flavor comes from lipolysis.Psychrotrophic bacteria in raw milk are inactivated by pasteuisation

75. DefectSpoilage BacteriaEnzymesMetabolic productAcid proteolysisSpoilage bacteria, Lactobacillus,Micrococcus,B. cereusProteasesPeptides,aminoacidsAlcholic flavorYeastsAlcohol deyhydogeanaseEthanolBitter flavorPsh. Bacteria, BacillusProteasespeptidasesBitter peptidesBarny flavorstoragePoorly ventilationacetoneCoagulationBacillusProteasesCasein destabilizationFishnessAeromanas hydraophilaFish flavorFruity flavorPseudomonas fragi, yeasts, moldsEsteraseEthyl esters, lactonesTable5.2. Some defects of fluid milk due to bacterial growth

76. a)SouringIf storage temperatures are sufficiently high for acid producing fermentative bacteria or presence of inhibitory compounds to Gram negatives result in souring.Genera of LAB causing spoilage of milk and fermented products;Enterococcus, Lactobacillus,Lactococcus,Leuconostoc,Pediocoocus, and Streptococcus.In raw milk at temp from 10-30 ˚C- L. lactis ssp lactisAt higher tempertaures-37-50 ˚C-S.thermophilus and E. facecalis and finally lactobacillus growLittle acid formation occurs near freezingUnpleasant sour odor and taste comes from acetic and propionic acid.A malty flavor comes from L. lactis. ssp lactis var. maltigenes.Most LAB can produce extracellular polymers that cause rope defect.Lactose positive coliforms produce acid and also gases and cause curdling, foaming and souringSome alcaligenes ssp and coliforms can cause ropiness.

77. b)ProteolysisProteolytic bacteria (e.g. Alcaligenes,Bacillus,Clostridium,Flavobacterium,Microcoocus,Pseudomonas,Proteus,Serratia ) cause proteolysis.The hydrolysis of proteins by m.o’s at low temperatures produces a bitter, fruity pudrid flavors due to release of peptides.Types of proteolysis;Acid proteolysis;Acid production and proteolysis occur together2.Proteolysis with little acidity and alkalinity3.Sweet curdling-by rennin like enzymes of bacteria4.Slow proteolysis by intracellular enzymes of bacteria after autolysis5.Residual proteolytic activity of heat stable proteinases in heat treated milk and products.

78. Factors affecting protease productionP. fluorescens and other psychrotrophs produce proteases during late exponential and stationary phases of growthThe effect of temperature on protease production does not parallel its effect on growth(Relatively high amount of protease are produced at temp as low as 5 ˚C.Protease production is inhibited at 2 ˚CThe most important characteristic of protease is their extreme heat stability( D values at 140 ˚C range from 50-200 s and sufficient to retain significant activity after UHT milk processing)UHT milk appears to be more sensitive to protease-induced defects than raw milk due to either heat-induced changes in casein micelle structure or heat inactivation of protease inhibitors.

79. ii)Protease induced defectsProteases hydrolysis casein and liberate bitter peptides.Bitterness is a common off flavor in past. milk, that comes from postpast. contamination with psychrotrophic bacteria.Putrid flavor is related with ammonia, amines and sulfides.Bitterness in UHT milk develops when sufficient pschrotrophic bacterial growth occurs in raw milk(105-107/ml)The effect of proteases of psychrotrophic bacteria in cheese and other cultured dairy product is low pH and lowe storage temp.

80. c)LipasesPsychrotrophic P. fluorescens , P. fragi and P. aeruginosa often produce extracellular lipase in milk.Milk fat may be decomposed by various bacteria, yeast and molds.Oxidation of the unsaturated fatty acids results with formation of aldehydes, acids and ketons to odors and tastes.Species of lipase forming bacteria (e.g. Alcaligenes,Bacillus,Clostridium,Micrococcus,Pseudomonas, Proteus, Staphylococcus and yeast) hydrolyze the milk fat P. fragi and S. aureus produce fairly heat resistant lipases. Lipase hydrolyses butter fat to fatty acids and glycerol. Combined effect of oxidation and hydrolysis produce rancidity.

81. i)Factors affecting lipase production and activityLipases of psychrotrophic Pseudomonas, like protesaes, are produced in the late log or stationary phase of growth.Optimal synthesis of lipase generally occurs below the optimum growth.For ex; optimum temperature for production of lipase is 8 °C for P. Fluorescens that exhibited optimum growth at 20 °C.

82. Lipase induced product defectTriglycerides in raw milk are present in globules that are protected from enzymatic degradation by a membrane. Milk becomes susceptible to lipolysis if this membrane is disrupted by excessive shear force (from pumping, agitation,etc).Raw milk contains mammalian lipase and most cases of rancidity in raw and pasteurized milk can be a result of this process, rather than from the growth of lipase-producing microorganisms.Sufficient bacterial lipase can be produced in raw milk to cause defects in products during processing and storage.Fatty acids of higher molecular weight produce a flavor described as soapy.

83. d.Ropiness and sliminessRopiness and sliminess result from microbial and non microbial actions.Responsible m.o’s may be Enterobacter aerogenes, Enterobacter clohiaacea, Escherichia coli, Klebsiella oxytoca,Lb. Bulgaricus, L. lactis ssp. cremoris, L. lactis ssp. lactis,Lb. casei,Lb. plantarum.The main sources of bacteria causing ropiness are water, manure, utensils and feed.

84. d.Ropiness and sliminessRopiness and slimines result from non microbial actions.1.May be due to fibrin and leucocytes(from mastitis)2.Result from the thickness of cream(at the top)3.May be due to films of casein and albumin

85. d.RopinessRopiness and sliminess can occur in milk, cream.Bacterial ropiness is caused by slimy capsular material from the cells and ordinarily develops best at low temperature.The ropiness usually decreases as the acidity of the milk or cream increases.Two main types of ropiness: Surface ropiness(caused by Alcaligenes viscolactis and Micrococcus freundenreichii ) and Ropiness throughout milk(E. cloacea,E. coli and K. oxytoca)

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87. e.Flavor ChangeDifferent off-flavors are caused by microorganismsSour or acid flavor is produced by Lc. Lactis.Volatile fatty acids are produced by coliform and Clostridium.2. Bitter flavors result from proteolysis and lipolysis flavor3. Burn or caramel flavor is caused by L. lactis var. maltigenes which resembles the cooked flavor of overheated milk4.Miscellenous flavor: barny flavor is caused by Enterobacter oxytocum, soapiness with ammonia production by P. sapolactica, malty flavor by yellow microccocci,fruit flavor by P. fragi,proteolytic flavor by P. mucidolens, fishness by Aeromonas hydrphila, putrefection by Clostridium and Pseudomonas putrefaciens, and alcoholic flavors by yeast. Lactones, which can impart a burnt, fruity, stale or coconut-like flavor to dairy products can be produced by various microbial reactions such as yeasts(e.g.Candida and S. cerevisiae) and molds (e.g. Penicillium notatum and .Cladosporium butyri)

88. f.Color changes Pigmented bacteria or molds may change the color of milk1.Blue milk: Pseudomonas syncyanea when grow with Streptococcus lactis2.Yellow milk: Pseudomonas synxantha and species of Flavobacterium.3.Red milk: Serratia marcescens, Micrococcus roseus4.Brown milk: Pseudomonas putrefaciens

89. g.Gas ProductionChief gas former are coliform bacteria, Clostridium spp., gas forming Bacillus species that yield both hydrogen and carbondioxide, yeasts and heterofermentative Lactobacillus that produce only carbon dioxide.Gas production evidenced by foam at the top of milk and is supersaturated with the gas, by gas bubbles caught in curd, by floating curd containing gas bubbles, or by a ripping apart of the curd by rapid gas production, causing the so called stormy fermentation of milk.

90.

91.

92. Spoilage of Vegetables and Fruits

93. InroductionThere are biological and physical agents spoiling vegetables and fruitsSpoilage caused by insect damage, physical injury, enzyme activity, microbial growth, action of animals, brushing, wounding, bursting, cutting, freezing, drying, etc.

94. II. Spoilage of Vegetables and FruitsSpoilage is not only undesirable ,but spoilage can also increase food safety risks by making microenvironment more suitable for human pathogens such as Salmonella enterica ser. typhimutium grows better on tomatoes, potatoes and onions ,in the presence of the spoilage molds Botrytis or Rhizopus.

95. Spoilage of Fruits and Vegetables

96. Vegetables Typical composition: -88% water -8.6 % CHO.  Includes readily available mono- and disaccharides like glucose and maltose, as well as more complex oligosaccharides, which are available to fewer types of microorganisms. -1.9% protein -0.3 % fat -0.84 % minerals -also contain fat and water soluble vitamins and nucleic acids (<1%). -pH of most veggies is around 6.0; within the growth range of many bacteria.

97. VegetablesVegetables are a good substrate for yeasts, molds or bacteria It is estimated that 20% of all harvested fruits and vegetables for humans are lost to spoilage by these microorganisms. Because bacteria grow more rapidly, they usually out-compete fungi for readily available substrates in vegetables.  As a result, bacteria are of greater consequence in the spoilage of vegetables with intrinsic properties that support bacterial growth (favorable pH, Eh).

98. VegetablesMicroflora of vegetables is primarily composed of:G+ bacteria like lactic acid bacteria (e.g. leuconostocs, lactobacilli, streptococci.Coryneforms and staphylococci (the latter coming from the hands of employees during processing.   Staphylococci are usually unable to proliferate but cross-contamination can introduce them into other foods where growth conditions are more favorable. 

99. VegetablesSoft rota.   One of the most common types of bacterial spoilage.b.   caused by Erwinia carotovora and sometimes by Pseudomonas spp., which grow at 4oC Softening can also be caused by endogenous enzymes.

100. VegetablesMold spoilagea.   In vegetables where bacterial growth is not favored (e.g. low pH), molds are the principal spoilage agents.b.   Most molds must invade plant tissue through a surface wound such as a bruise or crack.c.   Spores are frequently deposited at these sites by insects like Drosophila melanogaster, the common fruit fly.d.   Other molds like Botrytis cinerea, which causes grey mole rot on a variety of vegetables, are able to penetrate fruit or vegetable skin on their own. 

101. VegetablesThe microflora of vegetables will reflect:      a.   the sanitation of processing steps.      b.   the condition of the original raw product. - Soil-borne MO such as clostridia are common on raw vegetables, and some species, like C. botulinum, are of such great concern that they are the focus of processing steps designed to destroy MO.

102. VegetablesSources of Contamination1.   Surface contamination – Soil, water, air, human pathogens from manure (night soil)2.   Harvesting - hand picking vs. machines3.   Packaging: containers reused4.   Markets – handling, cross-contamination

103. FruitsAverage composition      -85% water      -13% CHO      -0.9% protein (a bit low on nitrogen sources)      -0.5% fat      -0.5% ash      -trace amounts of vitamins, nucleotides, etc.      -less water and more CHO than veggies      -low pH (1.8-5.6) 

104. FruitsLike vegetables, fruits are nutrient rich substrates but the pH of fruits does not favor bacterial growth.  As a result, yeasts and molds are more important than bacteria in the spoilage of fruits. a.   Several genera of yeasts can be found on fruit.b.   Because these organisms grow faster than molds, yeast often initiate fruit spoilage.c.   then molds finish the job by degrading complex polysaccharides in cell walls and rinds.

105. FruitsSpecific Spoilage Organisms:  1. Blue rot – Penicillium (fruits) 2. Downy mildews – Phytophora, large masses of mycellium (grapes)  3. Black rot – Aspergillus (onions)  4. Sour rot – Geotrichum candidum

106. A)Types of spoilage1.Active spoilage is caused by plant pathogenic m.o’s reduce sensory quality)2.Passive or wound induced spoilage(Opportunistic m.o’s enter into internal tissues through damged epidermal tissue)3.Soft rot –it is result from softening of the plant tissue(by mostly Erwinia carotovora and occasionally Pseudomonas, Bacillus, Clostridium, yeast, molds)

107. 1.Mechanism of SpoilagePlant cells have a variety of defense mechanisms to resist microbial invasion. These defense mechanisms must be overcomed before microbial spoilage.Fruits, vegetables and grains have an epidermal layer of cells such as skin, peel, or testa and it provides protection against microbial infection of internal tissues. If this barrier is damaged, m.o’s easily can enter.

108. 2.Degradative EnzymesMicrobial enzymes are mainly responsible for degradation of plant products. These are pectinases, cellulases, proteases,phosphatidases and degydrogenases. Pectin and cellulose are the main structural components of plant cells and pectinases,cellulases are the most important degradative enzymes involved in spoilage.Pectinases are group of pectic enzymes and cause depolymerization of the pectin chain. PME(Pectin methyl esterase)hydrolyses ester group of pectin chains with production of methyl alcohol.PG(Polygalactronose) and PL(pectin lyse)are chain splitting pectinases and reduces overall length of pectin chain.Cellulases degrade cellulose (a glucose polymer)to glucose.Its activity contributes tissue softening with formation of glucose.

109. B)Vegetable SpoilageThey are rich in CHO’s(5% or more), low in proteins(about 1-2%)and except tomatoes, have high pHa)Microbial Contaminationcomes from soil water, air and other environmental sources. Heat resistant spores can contaminate.Bacterial counts on fresh vegetables can range from 102 to 107 per g. Processing operations damaging vegetable tissues can increase microbial populations1. Poorly sanitized equipments can harbor contaminants2.Cutting and slicin g allow vegetable tissue fluids flow.

110. a)Microbial contaminationFresh vegetables contain microorganisms coming from soil, water, air, and other environmental sources. Heat- resistant spores of spoilage bacteria can contaminate from these sources.Processing operations damaging vegetable tissues can increase microbial populations in several ways;a)Poorly sanitized equipment can harbor contaminants and they are transferred to vegetables during the cutting operation. For ex. Geotrichum candidum (a machinery mold) can accumulate on processing equipment and contaminate vegetables upon contact. b)Cutting and slicing allow vegetable tissue fluids flow onto outer surfaces of the vegetable as well as the processing equipment. These fluids result in biofilm formation on vegetables and equipments

111. b)Microbial SpoilageBacteria frequently associate with initial spoilage defects. This is due to faster growth rate of bacteria than yeast or molds and therefore has competitive advantage.Spoilage of vegetables can be influenced by land on vegetables are grown.Processing steps on vegetables before consumption can increase changes for spoilage.

112. Microbial spoilageErwinia and Pseudomonas are the most important genera causing vegetable spoilage.Erwinia carotovora causes soft rot on vegetablesThey produce pectinase and protopectinase to hydrolyse protopectin. Erwinia carotovora var. Carotovora casuses black leg of patotoes at 25˚C.

113. Microbial spoilageSliminess or souring can be caused by bacteria on vegetables.Thermophilic spore-forming bacteria usually cause spoilage of canned vegetables.Acidification without gas production is one of the most common types of spoilage observed in canned vegetables. It is called a «Flat sour» is caused by B. stearothermophilus or B. coahulans.This defect ordinary occurs when inadequate thermal treatments or if cans are stored at temp’s above 40˚ C.Swelling is another spoilage caused by thermophilic spore forming aneorobes such as Clostridium thermosacchhhhharolyticum.They produce large amounts of hydrogen and CO2 gas.The production of H2S in some canned vegetables can lead to a spoilage problem known as «sulfide stinker» caused by D. nigrificans,C. bifermentans, and C. sporogenes.

114. Microbial spoilageSoft rot-Rhizopus. It produces cottony appearancesGray spots-BotryticusGreenish brown spots-Alternia tenuisGreen rot-Pencillum digitatumWatery soft-SclerotiniasclerotoriumStem and rots-Alternaria,Diploa,Fusarium,Phomopsis,and others.Black rot-A. niger,Alternaria,Cerostomella,Physalospora,Pink rot-Trichothecium rosum,Green rot-Cladosporium and TrichodermaBrown rot-Monilinia fructicola

115. c)PreservartionRefrigerationVacuum or MAP-reducing concentration of oxygen with increasing CO2WashingBlanchingPreservation by canning

116. C)Fruit SpoilageThe composition of fruit is about 85% water,13%CHO,0.9% protein, 0.3%fat and 0.5% ash.The pH range of fruits is 4.5 or below and this pH does not allow bacteria growth. Molds,yeast and aciduric bacteria (LAB, Acetobacter and Gloconobacter) are able growth and spoil fruit.

117. a)Microbial Spoilage of FruitsMany types of yeast are able to ferment sugars with the production of alcohol and CO2.

118. b)PreservationRefrigeration, freezing, drying, reducing water activity, washing and heat treatment reduce spoilage m.o’s. Filtration and blenching can also be used.Fruits are present in low pH values

119. III. Soft Drinks, Fruit Juices and Vegatable juicesCarbonated and noncarbonated soft drinks, fruit juices and concentrated fruit juices are high acid products(2.5-4.0)CHO content ranges from 5-15% in fruit juices and soft drinks, but 40-60%in concentrates and preserves. High sugar content reduces of concentrates.Vegetable juices contain sugar but less acid(pH between 5.0-5.8and support LAB. Yeast and molds can grow.Only aciduric molds, yeast and bacteria can cause spoilage in juices if appropriate preservation are not used.Yeat species (Torulapsis,Candida,Pichia,Hansenula and Saccharomyces can grow and make turbid in the carbonated beverages. Some species of Lactobacillus and Leuconostoc can also grow and cause cloudiness and ropiness(due to production of dextrans)Molds and Acetobacter can grow in the presence of enough dissolved oxygen. Acetobacter will produce acetic acid to give vinegar like flavor and further acetic acid can be converted to CO2.

120. III. Soft Drinks, Fruit Juices and Vegetable juicesYeast can oxidase organic acids to produce CO2 and H2O and ferment to alcohol abd CO2.Heterofermentative L. fermentum and Leu. mesentorides can ferment CHO to produce lactate,ethanol,acetate,CO2, diacetyl, and acetoin.L. mesentorides and some strains of L. plantarum can also produce dextran to cause slime Tomato juice has a pH of about 4.3.Generally high heat treatment is applied on tomato juice and this kills vegetative bacterial spores can survive. Germinaton and growth of B. coagulans spores in tomato juice can cause flat sour spoilage

121. Spoilage of Cereals andCereal Products

122. Cereal and Bakery GoodsThese products are characterized by a low aw which, when stored properly under low humidity, restricts all MO except molds.  Rhizopus stolonifer is the common bread mold, and other species from this genus spoil cereals and other baked goods.  Refrigerated frozen dough products have more water and can be spoiled by lactic acid bacteria.

123. The wheat is the major cereal of the world , and is grown extensively in both northern and southern hemispheres whereas durum wheat is grown extensively in the Mediterranean region,Asia, America.

124. CEREAL PRODUCTSCereal products, include food products resulting from the processing of various cereal grains.

125. Cereal and cereal products are grains themselves, meals, flours, alimentary pastes, breads, cakes and other bakery products.

126. The most important cereal grain supply are: wheat, rice, corn, rye, barley, oats, millet, sorghum and buckwheat. According to the normal rules of human nutrition grain products form the basis of the food pyramid and should be in your daily diet in the largest quantities.

127. WheatWheat is the most widely used in the manufacture of flour. There are different types of this flour, such as white flour, whole wheat and wheat middlings.

128. MaizeMaize has many applications and it can be used for the production of oil, alcohol, starch, flour.

129. RiceRice is the main food product for the majority of the world's population. Rice comes in many variations, depending on the grain size, and color and texture. For food purposes rice has to be boiled.

130. OatOat is used for the production of oatmeal, used primarily to making porridges, cakes, various pastries and muesli (granola).

131. RyeRye is used for making rye bread and certain alcoholic products.

132. Barley Barley as barley is used in soups and as malted barley - used in brewing beer.

133. DurumDurum is a type of wheat which is rich in protein. It is used for the manufacture of macaroni, noodles, dumplings, couscous and bread.

134. BreadWheat (and other grains) is hard to eat raw, and not very digestible. In the oldest times, wheat was ground up and cooked with water in a stew. Bread is far more digestible and storable.At its simplest, bread is made by mixing flour with water, then baking it. Adding salt helps with flavor. And, salt is necessary for humans but not much found in plants.

135. Grains are ground into flour or meal for bakery or pasta products, or further processed into snacks or breakfast cereals. Final products ,except dough often have aw below 0.65,which most microorganisms will not grow.The major factors involving in the spoilage of grains by molds are moisture levels(above 12%),physical damage and temperature. Grains normally have10-12%moisture,which lowers aw to ≤0.6.If aw increases above 0.6 during harvesting,processing and storage,some molds can grow.

136. Cereal Grainsa)Spoilage Before HarvestMold invasion is most prevalent during humid and rain weather.The main genera producing mycotoxins in preharvest are Aspergillus, Alternaria and Fusarium.Mycotoxins are toxic secondary metabolites produced by molds.They can be produced at any stage during the processing or storage of cerealcrops under favorable growth conditions. The genera of molds mainly associated withNaturally occuring toxins are Aspergillus, Penicillium and Fusarium. Some examples of mycotoxins occuring cereals are listed in Tableb)Spoilage During StorageDuring storage , the field molds on grain are replaced by molds capable of growing at a lower aw.Spoilage will occur during storage if the overall moisture content of grain s is sufficiently high to support mold growth.The main genera of molds casuing spoilage during storage are Aspergillus and Penicillium

137. GrainsTypical Discoloration of grainA. fumigatusDiscolored germs(dark blue-green)A. penicillioidesDiscolored germs, blue eye of maizeA. candidusPowdery white patchesA. flavus Greenish discolorationA. nigerPurple-brown to clack color on breadA. ochracesuDiscolored germsEurotiumDiscolored germs, green eyeFusariumRed streaking, particularly on maizePenicilliumBlue coloration, blue eye of maizeAlternariaDarkening of grainBreadTypical Discoloration of BreadMont. sitophilaPink or reddish colorP. expansumGreen sporeP. stoloniferuWhite cotton colorYeast and LABSour taste, off flavorVisual Characteristics of some molds spoilage on cereal grains and products

138. Grain HeatingRespiration of moist grain is responsible for the heating of stored grains. Research has subsequently proven that the metabolic processes of storage fungi are responsible.Heated grain does not become moldy, but just the opposite ;moldy grain becomes heated.

139. Species of fungusMinimum temperatureOptimum temperature(°C)Maximum temperatureMinimum aw for growthA. restrictus<1525-30>370.75A. penicllioides930400.7Eurotium425-2740-500.59A. candidus1245-5050-550.75A. flavus103342-470.80A. versicolor102534-400.76Penicillium1020-3128-400.79Table. Average minimum, optimum and maximum temperatures and minimum aw for the growth of common storage molds on grain

140. CONTAMINATIONThe exteriors of harvested grains retains some of the natural flora they had while growing plus contamination from soil ,insects & other sources. Freshly harvested grains contain loads of a few thousand to million of bacteria /gm and mold spores Bacteria are mostly in the families Pseudomonas, Micrococci, Lactobacilli and Bacilli.Scouring & washing the grains remove some of the microorganisms, but most of the microorganisms are removed with the outer portions of the grains during milling.The milling processes especially bleaching reduce no. of organisms.

141. Cont….Corn meal and flour contain several hundred to several thousand bacteria and mold per gram. Species of fusarium & penicillum are dominant molds. Because of the incubation in a moist conditions , malts contain high numbers of bacteria , usually in the millions per gram. the surface of freshly baked bread is free of viable microorganisms but is subject to contamination by molds spores from the air during cooling & before wrapping .cakes are similarly subject to contamination .spores of bacteria able to cause ropiness in bread will survive the baking process.the contamination of cereals grains products with molds has become a significant concern because of the presence of mycotoxin.

142. Cont….But there then is possibility of contamination during other procedures such as blending & conditioning.Bacteria in wheat flour include spores of Bacillus , coliform bacteria ,and few representatives of the genera Achromobacter ,Flavobacterium , Sarcina ,Micrococcus and Serratia. Mold spores are of aspergilli ,penicillia ,alternaria & cladosporium.patent flours usually give lower counts than straight or clear & no. decreases with storage of flour.Higher counts usually are obtained on prepared flours (8000 to 12000 per gram on the average) & whole-wheat flours, which contain also the outer parts of wheat.The need to reduce contamination by mold and to avoid conditions which allow their growth is emphasized because of frequent isolation of Aspergillus flavus , which can produce aflatoxin.Some commonly isolated molds such as fusaria & penicillia are undesirable since they are capable of producing mycotoxins.

143. Table. Types of mycotoxins produced in cerealsMold speciesMycotoxinsparasiticusA. flavusAflatoxin B1, B2,G1,G2,M1,M2Fusarium sporotrichioidesTrichothecenes:T-2 toxin,HT-2 toxin, neosolaniolF. gramineraumDeoxynivalenol, niavalenol,zearalenoneF. moniliformeFumonisins, FusarinPenicillium islandicumIslanditoxin, luteokyrinP. citreovirideCitreoviridinP.citrinumcitrininClaviceps purpureaErgotamineA. Ochraceus,P. verrucosumOchratoxin A

144. PRESERVATIONMost cereals and cereal products have such a low moisture content that there is little difficulty in preventing the growth of microorganisms as long as the foods are kept dry .Such materials are stored in bulk or in containers to keep out vermin , resist fire and rapid changes in temperature and hence increase in moisture.The storage temp. of about 4.4 to 7.2c is recommended for the dry products.Many bakery products eg. bread ,rolls, cakes, pastries &canned mixes contain enough moisture to be subject to spoilage unless special preservative methods are employed.

145. Methods areAsepsis: improperly sanitized equipments may be source of rope bacteria and the acid –forming bacteria that cause sourness of dough. bread ,cakes and other baked products may be subject to spoilage by molds should be protected against contamination by mold sporesUse of heat :bakery products may be sold unbaked ,partially baked or fully baked .the complete baking process destroys all the bacterial cells, yeasts ,mold spores but not spores of rope –forming bacteria.they can survive during heat so unbaked products are kept for short period or kept cool during longer storage of time.Use of low temp. :baked products should be kept under cool conditions or refrigerated in home for the prevention of food spoilage. These can be stored for months in the frozen conditions.

146. Con…..Use of chemical products :a large no. of preservatives have been employed ,particularly as mold inhibitors , in breads , rolls , cakes . Sodium and calcium propionate , sodium diacetate and sorbates are used extensively .acidification of dough with acetic acid has been used to combat rope.Use of irradiation :in bakeries , ultraviolet rays have been to destroy or reduce numbers of mold bacteria in dough and proof rooms, on the knives of slicing machine , on the surface of breads ,cakes .ionizing radiations , gamma and cathode rays have been applied experimentally for the preservation of baking goods.

147. spoilage Cereals grains ,meals &flours made from them should not be subject to spoilage if are stored or kept properly because their moisture content is too low to support even the growth of molds. Now different cereal products are discussed below :Cereal grains &meals :a little moisture will result in growth of molds at the surface , where air is available. A wet mash of the meals will under go an acid fermentation by lactic acid and coliform bacteria normally present on the surface of plants. This may be followed by the alcoholic fermentation by yeasts as soon as the acidity is increased enough to favor them . The major factors included in the spoilage of stored grain by molds include microbial content , moisture levels above 12 to 13 %, physical damage & temperature. Most common species of molds are Aspergillus , Penicillium and Fusarium.these molds can produce mycotoxins .

148. Con…Flour : Dry cleaning and washing , milling & sifting of flour reduce the content of m.o., but important kinds still are represented in whole –grain flours e.g. and the spoilage would be similar to that described for cereal grains and meals. Slight moistening of white flour brings about spoilage by molds. Because of the variations in microbial content of different lots of flour , the type of spoilage in a flour paste is difficult to predict. If acid –forming bacteria are present , an acid fermentation begins , followed by alcoholic fermentation by yeasts if they are there and then acetic acid by Acetobacter species. In the absence of lactics and coliforms , micrococci have been found to acidify the paste .

149. Cont…Bread : the fermentation taking place in the dough for various kinds is due to microorganisms are desirable and even necessary in making certain kind of bread .the acid fermentation by lactics and coliform bacteria that is normal in flour pastes or dough may be too extensive if too much time is permitted , with the result that the dough bread made from it may be too ‘sour’ . excessive growth of proteolytic bacteria during this period may destroy some of the gas –holding capacity so essential during the rising of the dough & produce a sticky dough. the chief types of microbial spoilage of baked bread have been moldiness and ropiness , usually termed “mold” & “rope”.

150. Causes of spoilage Mold : molds are the most common and hence the most important cause of the spoilage of bread and most bakery products. The temp. attained in the baking procedures usually are high enough to kill all the molds spores in and on the loaf. They can come from the air during cooling , from handling or from wrappers .chief molds involved in the spoilage of bread are “bread mold”, rhizopus nigricans with its white cottony mycelium and black dots of sporangia ;the green –spored Penicillium expansum;aspergillus Niger with its greenish or purplish –brown conidial heads and yellow pigment diffusing into the bread. Mold spoilage is favored by - heavy contamination due to air circulation . During slicing when there is more air is introduced into the loaf .

151. Cont….Wrapping ,especially if the bread is warm when wrapped & storage in a warm , humid place .Rope – ropiness of bread is fairly common in home baked bread, especially during hot weather ,but it is in commercially baked bread because of preventive measures now employed .ropiness is caused by a mucoid variant of Bacillus subtilis .the spores of these species can withstand the temperature of the bread during baking , which does not exceed 100 ̊c , can germinate &can grow in the loaf if conditions are favorable. The area of ropiness is yellow to brown in color & is soft ,sticky to touch. In one stage the slimy material can be drawn out into long threads when the bread is broken and pulled apart.first the odour is evident ,then discoloration and finally softening of the crumb , with stickness and stringiness.

152. Rope formation is a serious, but under reported food security problem in the bakery industry.  Although ropiness has been recognized for many years, no effective means of prevention have yet been determined.  Ropiness can occur in wheat bread, mixed grain bread or yeast-raised baked goods. It is initially characterized by an unpleasant fruity odor accompanied by a bitter taste. Subsequently the bread crumb discolors, the bread appears greasy and sticky and, when broken apart, extended threads develop which stretch out from the crumb. Ropiness is is caused by several bacterial species of the genus Bacillus (B. subtilis, B. licheniformis, B. pumilus, B. megaterium, and B. cereus)

153. Ropiness and moldiness in breads

154. Red bread“Red or bloody” ,bread is striking in appearance but rare in occurrence .the red color results from the growth of pigmented bacteria, usually serratia marcescens , an organism that often is brilliantly red on starchy foods. Molds such as Monilia Sitophila may impart a pink to red color to bread .a red color in the crumb of dark bread has been caused by Oidium Geotrichum.Chalky bread : chalky bread is so named because of white , chalklike spots .the defects has been blamed on the growth of yeast like fungi, Endomycopsis fibuligera and Trichosporon variable.Cakes and other bakery products: molds are main cause of spoilage in cakes .the deterioration of bread , cakes , pies and other bakery products caused “staling” is due to physical damage during holding and not to microorganisms. Freezing and storage in the frozen conditions is effective in preventing these changes.

155. Spoilage by moldschalky bread

156. Spoilage of Canned Foods

157. CanningCanning is a method of preserving food in which the food contents are processed and sealed in an airtight container. Canning provides a shelf life typically ranging from one to five years, although under specific circumstances it can be much longer. 

158. CANNING

159. Canning means, the preservation of food in permanent, hermetically sealed containers (of metal, glass, thermostable plastic, or a multi-layered flexible pouch) through agency of heat. Heating is the principle factor to destroy the microorganisms and the permanent sealing is to prevent re-infection.CANNING

160. Important canned food groups

161. Procedure

162. ProcedureThe canning process itself consists of several stages: Cleaning- passing the raw food through tanks of water or under high-pressure water sprays Preparing the raw food material- vegetable or other products are cut, peeled, cored, sliced, graded, soaked, pureed, and so onBlanching- immersion in hot water or steamFilling the containers- usually under a vacuum; Closing and sealing the container- done automatically by machines; cans are filled with solid contents and, in many cases, with an accompanying liquid (often brine or syrup) in order to replace as much of the air in the can as possibleSterilizing the canned products- they are heated at temperatures high enough and for a long enough time to destroy all microorganisms (bacteria, molds, yeasts) that might still be present in the food contents. The heating is done in high-pressure steam kettles, or cookers, usually using temperatures around 240° F (116° C).Labeling and warehousing the finished goods- cans are then cooled in cold water or air, after which they are labeled.

163. Spoilage of Canned Foods

164. Contd..Botulism caused by Clostridium botulinum  produce toxin in a sealed jar of food. Home-canned vegetables are the most common cause of botulism outbreaks in the United States.From 1996 to 2008, there were 116 outbreaks of foodborne botulism reported .These outbreaks often occur because-home canners did not follow canning instructionsdid not use pressure cookers/cannersignored signs of food spoilagewere unaware of the risk of botulism from improperly preserving vegetables.

165. Spoilage in canned foods may be due to the growth of microorganisms (bacteria, yeasts, and molds), or to chemical action. Spoiled cans may be of two kinds, swells and flat sours. Swells are caused by microorganisms which produce gas. Flat sours result from microorganisms that produce acid, but little or no gas. Swells may be of all degrees of tightness, from cans having only one end slightly bulged to those in which both ends are so distended that the tinplate buckles. These variations may be due either to the time which has elapsed since the spoilage microorganisms began to multiply, or to the type of microorganism causing the spoilage, since some produce much more gas than others. Swelling may also occur due to the chemical action of the food on the metal of the container, with the production of hydrogen gas.

166. Signs Of SpoilageIn cans, the only visible evidence of spoilage in unopened containers is the condition of the ends. If these are bulged to any degree, the can may contain spoiled product. Most spoiled food will have a somewhat turbid (cloudy) brine or syrup, but this is not always the case. In jars, a white deposit may sometimes be seen on the bottom or on the pieces of food. This may be a sign of spoilage, but it is not always so, as starch is sometimes precipitated from certain foods. An off odor is frequently an indication of spoilage, but some spoiled food has no noticeable off odor.

167. Can Swelling Of Non-Microbial OriginCertain products, particularly those of low pH (high acidity), are more or less corrosive to metal of the container. As corrosion progresses, hydrogen gas is evolved. These cans eventually become swells. There are some products high in sugar which may break down chemically while in storage, particularly if storage temperatures are too high. The breakdown causes the evolution of carbon dioxide gas. Another cause of swelling may be overfilling, particularly in the smaller size cans or those with a large lid area in proportion to height. A fourth cause of swelling may occur when cans with a low initial vacuum are transported to areas of higher altitude or elevated temperatures. The product in these cans is usually harmless and may safely be eaten. However, since the consumers have no way of determining the cause of a swollen can, they are advised not to use them.

168. How Spoilage Can OccurCanned foods may be spoiled by microorganisms due to incipient spoilage before processing, leakage through defective closures, or underprocessing. Sometimes there may even be a combination of these conditions.

169. Incipient Spoilage. The food may spoil during the period of preparation if it is allowed to stand too long at temperatures favorable for the growth of microorganisms, from 60° to 170° F. This is known as incipient spoilage before processing. Seam Leaks. The jars or cans may have defective seals or seams, and their contents may become contaminated with bacteria after processing by leakage into the container.

170. Underprocessing. The jars or cans may be underprocessed; i.e., they may not receive sufficient heat to destroy all the spoilage organisms which may grow during normal storage and distribution. In low-acid foods, spoilage due to underprocessing is particularly hazardous, owing to the danger of botulism. Spoilage of this type is often considerably delayed and may not develop for several weeks or even months after canning.

171. Retort By-Pass. The inclusion of unprocessed cans in a batch of cans that have been processed is a serious matter. This can occur in almost any plant with almost any retort system. It is imperative that all staff members be trained in the importance of retort bypass prevention in addition to having a bypass prevention system in place.

172. Foods may be divided into three main groups with regard to spoilage resulting from underprocessing: 1. Low acid (including vegetables (except tomatoes), meat, poultry, fish, milk and ripe olives). Bacteria which produce very heat-resistant spores, such as Clostridium botulinum, and thermophiles (heat-loving bacteria, growing best at 100° to 160° F.), can grow in these foods, all foods of this group require processing in a steam pressure cooker or retort.

173. 2. Acid (including fruits and tomatoes, and fermented and acidified foods). Spoilage organisms are usually easily destroyed by heat, and boiling water processes are sufficient for sterilization. Tomatoes and fruits which are low in acid, such as pears, require much longer processes than the more acid fruits, like cherries, plums and berries. Pickles, sauerkraut, and adequately acidified vegetables (pH below 4.6) can also be considered as acid foods, requiring only a boiling water process

174. 3. High acid and high solids content (including jams and jellies, catsup, chili sauce, etc.): Spoilage is usually due to molds and yeasts, microorganisms which can be destroyed in a few minutes at 170°F.

175. Types of Spoilage Organisms There are three main groups of microorganisms capable of causing spoilage in foods, namely -- molds, yeasts, and bacteria. Molds are fungi, and are widely distributed in nature. The growth consists of a network of threads (the mycelium) which penetrate the food in every direction. Mold is chiefly a problem in jams and jellies, in hot pack, unprocessed foods, and in containers which have leaked after processing. Yeasts, like molds, are widely distributed in nature and are found on nearly all exposed surfaces, and particularly on moist organic substances containing sugar and acid. The cells are easily destroyed by heat, a few minutes at 170°F being sufficient for even the most heat resistant.

176. Bacteria are the most important microorganisms with which the canner has to deal. There are a great many different species, able to grow under the most diverse conditions. Some are harmful, but many are highly beneficial. Bacterial cells are extremely small, but are capable of rapid multiplication in a favorable environment. Some bacteria can grow at low temperatures, nearly at the freezing point of water, and others at high temperatures, up to 170°F. The latter are called “thermophiles”, and are of considerable importance to canners, as they are common contaminants of certain foods and their spores are very heat resistant. Some bacteria (called “anaerobes”) can grow in the absence of oxygen, and others (called “aerobes”) require atmospheric oxygen for growth. A still larger group can grow either with or without oxygen.

177. Canned Food SpoilageGAS (Swelling)NO GASH2H2+O2CO2Thermophilic spoilageMesophilicAcid or rancid odorPutrid odorRancid or butyric odor(Clostridium,Bacillus)Facultative anearobeMixed Fermentation(Bacillus)H2S odor(Blackaning,rotton egg odor)Drop in pHMoldy(usually leakage)Thermophilic flat sour(Bacillus)Mesophilic1.Flat sour-Bacillus2.Mixed (Lactobacillus)3.Butyric Fermentation(Saccharolytic anaerobes)Hydrogen swellingBacillus or yeasts

178. Enzymatic and Nonenzymatic Spoilage of Food

179. IntroductionThe storage of foods is limited by non enzymatic, enzymatic or microbial reactions which alter edible quality; including deterioration, appearance, texture, aroma, flavor, nutritionon, safety and functional properties.As the number of bacteria increases, the amount of enzymes released by lysed cells increases.

180. Discoloration of the surface of red meats is caused by a nonenzymatic reaction with the oxidation of myoglobin (Fe+2) to form metmyoglobin (Fe+3) .Enzymatic reactions involved with respiration at the tissue surface can lower oxygen concentration and indirectly promote non enzymatic oxidation of myoglobin.Some muscle tissue contain the enzyme metmyoglobin reductase, which catalyzes the reduction of methmyoglobin back to myoglobin.

181. Hydroxylation of monophenol to o-diphenolDehydrogenation of o- diphenol to o-quinoneENZYMATIC BROWNINGPolyphenol oxidasePhenolic substrateO2O2O2O2O2O2O2Phenolic substratePolyphenol oxidase181

182. Non Enzymatic SpoilageIn the case of heat treated or other processed foods where enzymes have been destroyed or their activity has been arrested, nonenzymatic chemical reactions play a more important role in food spoilage than enzyme catalyzed reactions.Non enzymatic changes during food processing and storage will result in loss of quality. The two non enzymatic reactions in foods which appear to be most widespread importance are Maillard browning and lipid oxidation

183.  Maillard reaction is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor.The browning of various meats like steak, when seared and grilledThe browning and umami taste in fried onionsCoffee roastingThe darkened crust of baked goods like pretzels, bagels, and ToastThe golden-brown color of French fries and other cripsMalted barley found in maltwhiskey or beerDried or condensed milk

184. Non enzymatic SpoilageThe rate of non enzymatic reactions in foods is a function of one or more variables, including pH, temperature, ionic strength, concentration of reactions, presence of catalysts, mobility of reactants, oxidation reduction reactions, decompartmentation of reactants and the physical state of the reactions. One of the most important variables influencing chemical changes in food is temperature.

185. Arrhenius equation gives the influence of temperature on raction rateThe catalytic rate of reactions increases with a rise in temperature.k=Ae-EaRTæ è ç ö ø ÷ k = rate constantA = frequency factor for collisionsEa = activation Energy (J/mol)R = Gas constant (8.3145 J/Kmol)T = Temperature in Kelvin

186. The Arrhenius EquationThis relationship is summarized by the Arrhenius equation.Taking logs and rearranging, we get:lnk=-EaRæ è ö ø 1Tæ è ö ø +lnAk=Ae-EaRTæ è ç ö ø ÷

187. Enzymatic SpoilageFoods can contain low amounts of metabolizable carbohdrates (mono- and disaccharides),nitrogenous compounds(small peptides, aminoacids, nucleosides, nucleotides, urea, creatinine, trimethylamine oxide), free fatty acids and organic acids (lactic and malic acids)

188. Enzymatic SpoilageEnzyme-catalyzed processes may contribute to quality deterioration, particularly in processed foods.For example, for orange juice, a stable colloidal suspension is desired, the action of pectin methyl esterase(PME) is undesirable since demethylation of pectin, catalyzed by this enzyme, leads to separation of serum particulates in juice.Heat processing of orange juice to inactivat e PME is undesirable since nonenzymatic reaction adversely affects the delicate flavor of product.PME enzyme

189. Enzymes- Chemical reactionsChemical reactions need an initial input of energy = THE ACTIVATION ENERGYDuring this part of the reaction the molecules are said to be in a transition state.

190. Substrate concentration: Non-enzymic reactionsThe increase in velocity is proportional to the substrate concentration Reaction velocitySubstrate concentration

191. Substrate concentration: Enzymic reactionsFaster reaction but it reaches a saturation point when all the enzyme molecules are occupied.If you alter the concentration of the enzyme then Vmax will change too. Reaction velocitySubstrate concentrationVmax

192. EnzymeContribution of food spoilageAlkaline proteaseHeat stable alkaline protease can cause gelation in milk products processed at UHTAscorbic acid oxidaseLoss of vitamin C in orange juices and oter citrus juicesCellulaseResult in loss of texture integrity of plant foods and relasing glucoseChlorophyllaseRemoval of the phytol side chain from chloramphyll causes the degreening processLipaseHydrolyze milk fat releases short chain fatty acids leading rancidityLipoxygenaseFormation of specific hydroperoxidases can lead the bleaching PectinasesResults in loss of texture integrity of vegetables, frits and their products

193. EnzymeContribution of food spoilagePeroxidaseDecomposition of hydroperoxiades with generation of free radicals causes bleaching of pigments, off-flavor, etc. e.g. İn vegetablesPhospholipaseCause denaturation of muscle proteins and texture deterioration, e.g. İn fishPolyphenol oxidaseEnzmatic browing, e.g.., in fruits,shellfishProteinasesDecomposition of proteins with formation of amino acid and peptides to give bitter flavorThiaminasesDecompose thiamine in fermented products and reduce thiamine content, e.g., in shellfishTrimethylemine oxide demethylaseRelease formalehyde in frozen fish contributing protein aggregation and texture deterioration.

194. 3. Characteristics of heat stable Enzymes of PsychrotrophsWhen the raw milk is stored for long time at low temperature (chilling or refrigerator)before heat treatment of psychrotrophic microorganisms, the psychrotrophic bacteria can multiply and produce heat-stable enzymes. Heating, such as pasteurization and UHT, kills the psychrotropic bacteria but does not inactivate the heat-stable enzymes. These enzymes cause spoilage in heat-treated dairy products.

195. heat stable microbial enzymesSpecies from genera Pseudomonas (such as P. fluorescens, P. fragi), Aeromonas,Flavobacterium,Shewanella,Serratia and Acinetobacter produce heat stable extracellular proteinases.Pseudomanas,Alcaligenes,Shewenalla,acinotobacter and Serratia produce heat-stable lipases. Pseudomonas spp. can also produce heat stable phospholipases

196. 4)Spoilage of Foods with Heat-Stable Microbial EnzymesThe heat-stable enzymes produced by psychrotrophic bacteria can cause spoilage of products. When products are used as ingredients, they add heat-stable enzymes and these enzymes can reduce the acceptance qualities, such as heat stable proteinases and lipases can produce flavor defects in pasteurized milk.

197. a)Ultrahigh heat treated milk productsUHT treated milks, heated at 140 to 150 ° C for 5 to1s , are commercially sterile products with a shelf-life of 3 months at 20 °C. Spoilage of these products during storage at 20 °C with formation of bitter flavor and gel formation are caused by heat-stable proteinases and rancid flavor by heat-stable lipases. The spoilage caused by proteinases is more predominant than the lipases

198. b)CheesesProteolytic activity by the extracellular proteinases of psycrotrophic bacteria in raw milk reduce cheese yield and increase the levels of nitrogenous compounds in whey.The loss of cheese yield can be as high as 5% due to the proteinase activity

199. Cultured dairy productsGrowth of proteolytic bacteria in raw milk can produce heat-stable proteinases and lead to poor texture and rapidly development off-flavoring butter milk and yogurt during storage.Cream and butter are more susceptible to spoilage by heat-stable lipases than proteinases.Extracellular lipases of psychrotrophic bacteria cause off-flavor in cream. This causes foam excessively and takes longer time to churn. The butter prepared from such cream is susceptible to developing rancidy more.

200. Milk powderThe activity of heat-stable bacterial proteinases and lipases present in raw milk and these enzymes will not denaturated by pasteurization during the spray-dried milk powder pasteurization.The low aw will prevent degradation of proteins and lipids in dry milk by these enzymes.

201. Inhibition of enzymesEnzymes can e inhibited by one of the followings:Sulfite reacts with quinone to prevent further chemical stepspH in vinegar(citric acids)Heat treatmentSodium hexametaphosphate/ascorbate/citrateEDTA (binds copper of PPO (prophenoloxidase ))Sugar(limit oxygen diffusion)Vacuum packageCysteineBlanchingirradiation

202. Food Microbiology-Beneficial microorganism

203. Biological agents responible in Food FermentationsBacteria a)Lactic acid bacteria b)Types of commercial starter cultures c)Conditions required for bacterial fermentations d)Characteristics of important genera2.Yeasts3.Molds

204. Micro-organisms cause changes in the foods Help to preserve the food,Extend shelf-life considerably over that of the raw materials from which they are made,Improve aroma and flavour characteristics,Increase its vitamin content or its digestibility compared to the raw materials.

205. Biological agents responsible in Food FermentationsMost fermentations require several species, acting simultaneously and/or sequentially to give product with desired properties ,including appearance, aroma, texture and taste.Vinegar production is a joint effort between yeast and acetic acid forming bacteria. The yeast convert sugars to alcohol which is the substrate required by the Acetobacter to produce acetic acid through oxidation.

206. Bacteriaa)Lactic acid Bacteria i)Groups of LAB depending on glucose metabolism ii)Groups of LAB depending on growth temperatureb)Types of commercial bacterial starter culturec)Conditions required for bacterial fermentations

207. Lactic Acid Bacteria(LAB)İt is loosely defined as all members of fermenting bacteria producing lactic acid from hexoses and lack functional heme-linked electron transport system or cytochromes(no krebs cycle).Lactic acid bacteria  compose a group of bacteria that degrade carbohydrate (e.g., fermentation ) with the production of lactic acid. The principle genera of LAB are Lactobacillus,Lactococcus,Leuconostoc,Pediococcus, and Streptoccus(Table 2.2)

208. PropionibacteriumThey belongs to Propionibacteriacae family and responsible for flavor and texture of some fermented food products(especially Swiss cheese-eyes and holes formation)They break down lactic acid into acetic acid and propionic acid and CO2.The cells are Gr(+),pleomorphic thick rods or coccoids ,1-1.5µm.occur as in single cells,pairs,or short chainswith different configurations.They are nonmotile,nonsporulating,anerobic and aerotolerant,catalase positive.They grow optimally fro 30-37 Cwith pH 6.0-7.0.Some species form pigment.Species in dairy industry are Pro. freudenreichii,Pro. jensenii,Pro. thoeni,Pro. acidopropionia.

209. Acetic Acid BacteriaAcetobacter and Gluconabactera important two genera producing acetic acid. They are in the family They oxidaze alcohol to actic acid in the presence of excess oxygen.They are Gr(-),obligate aerobic,catalase positive,rods (0.5-1.5 µm),occuring single cells,pairs or chains or chains.motile or non motile.They grow between 25-30 ˚C.They present naturally in fruits, sake, alcoholic beverages,cane juice and soil.Acetobacter aceti

210. YeastA small number of yeasts is able to grow anaerobically and utilizes sugar to generate energy. The majority of these yeasts also grow aerobically. They have beneficial and non-beneficial effects on foods.Yeasts are unicellular organisms that reproduce asexulally by budding.Yeasts play important role in food industry as they produce enzymes that cause desirable chemical reactions such as leaving of bread and the production of alcohol and inverting sugar

211. S. cerevisia and its subspecies are used for producing bread,beer,wine,distilled liquor,industrial alcohol,invertase,and give flavor to some foods(e.g.soups).All Saccharomyce strains ferment glucose and many ferment plant associated carbohydrates such as sucrose, maltose and raffinose but not ferment the lactose.Yeasts associate w,th fermentation of foods to produce alcohol ,enzymes,single cell proteins and additives.A restricted number of yeasts are used in the fermentation. Saccharamyces spp. are used in the production of bread, wine, champania, alcohol,distilled licor and invertase enzyme.

212. Kluyveromyces marxianus,K. marxianus var. lactis hydrolyse lactose and associate with natural fermentation along with other yeasts and lactic acid bacteria in alcoholic dairy products such as kefir and kımız.Yeasts grow at low water activities in the presence of high concentrations of salt and sugar.

213. MoldsThey are aerobic organisms therefore they can nor carry out fermentation but produce extracellular enzymes. These enzymes hydrolyze large organic compounds to smaller units. These smaller compounds are utilized by fermentative bacteria and yeasts.Molds are important n food industry with respect to enzyme producers, spoilers and preservers of foods. Certain molds produce undesirable toxins and cause food spoilage.(The Aspergillus spp)The genus Penicillium associate with ripening and flavor of cheeses.A. niger is used in the production of citric and gluconic acid,,pectinase and amylase enzymes from glucose,sucrose and starch.Rhizopus oligosporum is used in te production of tempe.P. roqufortiii is used for ripening of Roquefort,Gorgonzola and Blue Cheeses, P. camabertii for Camemberti cheese and P. caseicolum for brine cheese.RoquefortCamembertiTempeGorgonzola