Lecture 2 Biological - PowerPoint Presentation

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Lecture

2Biological Agents responsible in Food Fermentations

FE308

- Fermentation TechnologySpring 2016

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Biological agents responible in Food Fermentations

Bacteria a)Lactic acid bacteria b)Types of commercial starter cultures c)Conditions required for bacterial fermentations d)Characteristics of important genera2.Yeasts

3.Molds

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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.

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Biological agents responible in Food Fermentations

Most 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.

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Role of fermenting microorganisms are;

Production of lactic acid, flavor, proteolytic activity, lipolytic activity, organic compounds, prevention of foodborne disease and spoilage, and change in texture of food. The most common groups of microorganisms involved in food fermentations are bacteria, yeasts and molds.

Microbial enzymes also play important role in food fermentations.In general, growth will be initiated by bacteria, fallowed by yeasts and then molds. The smaller microorganisms multiply and take up nutrients from the surrounding area most rapidly. Bacteria are the smallest of microorganisms, fallowed by yeasts and molds. The smaller bacteria, such as

Leuconostoc and Streptcoccus grow and ferment more rapidly than their close relatives.

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Bacteria

a)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

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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)

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Lactic Acid Bacteria

While this is a loosely defined group with no precise boundaries all members share the property of producing lactic acid from hexoses. As fermenting organisms, they lack functional heme-linked electron transport systems or cytochromes, they do not have a functional Krebs cycle.

Energy is obtained by substrate-level phosphorylation while oxidising carbohydrates.

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Genus

Cell MorphologyFermentationLactate

isomerLactococcusCocci in chainshomoLPediococcus

coccihomoDLSteptococcusCocci in chains

homoLLactobacillus

rodsHomo, heterofermDL,D,L

LeuconostoccocciheterofermD

Table

2.2.Principle

genera

of

the

lactic

acid

bacteria

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Microorganisms

CharacteristicsReactionsAcetobacter spp

acetiA. pasteurianumA. peroxydansAerobic Gram(-)

Rods,grow at aw ≥0.9Oxidase organic compounds (such as alcohols)to organic acids (acetic acids)

Streptoccus sppS. bovisS. t

hermophilusEnt. faecalis Gram(+)Tolerant

acid,grow at aw ≥0.9

Homofermentative

.

Common in dairy fermentations,

but E.

faecalis

is in vegetable products.

They can grow in high pH media

Leuconostoc

spp

L.

mesenteroides

L.

dextranicum

L.

paramesenteroides

L.

oenos

Gram(+)

cocci

Heterofermentative

. Produce lactic

acid,plus

acetic acid,

ethanol and CO

2

from glucose.

L.

oenos

utilises

malic acid and other organic acids in

wine.

Pediococcus

spp

P.

cerevisia

P.

acidilactici

P.

pentosaceus

Gram(+)

Cocci

pairs in tetrads

Saprophytic organisms present in fermenting vegetables,

mashes,

beer and wort.

They are important in

sucuk

fermentation.

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Microorganisms

Characteristics

ReactionsLactobacillus sppHomofermentativeHereformentative

Gram(+)Rods, Tolerate acid,grow at aw

≥0.9Metabolize sugars to lactic

and acetic acid ,ethyl alcohol, CO2 .

Produce lactic acidProduce

lactic

and

acetic

acid

,

ethyl

alcohol

,

CO

2 ,

partially

Reduces

fructose

to

mannitol

Yeasts

Sac.

cerevisia

Sac.

pombe

Candida,Geot

.

candidum

Tolerate

acid,40%

sugar

,

grow

at

aw

≥

0.85

Many

aerobic,some

anerobes

S.

Cerevisiae

can

metabolize

sugars

from

a

fermentative

to

an

oxidative

pathway,depending

on

oxygen

avalibility

.

Tolerate

high

salt

concentrations

and

low

aw

.

Molds

P.

roquefortii

P.

camembertii

Aerobic,tolerate

acid,grow

at

aw

≥

0.85

Metabolize

sugars

through

extracellular

enzymes

and

oxidation

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Groups of LAB on glucose

metabolismHomofermentersHeterofermenters

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Groups of LAB on

tempertauresMesophilic starter cultures(optimum growth temp range 20-30 ˚C)Thermophilic

starter cultures cultures(cultures(optimum growth temp range 40-45 ˚C)Miscellaneus

bacterial starter cultures cultures(optimum growth temp range 37-41 ˚C)

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Mesophilic starter cultures

They are used for production of fermented milk products such as fresh cheese, semi-hard cheese, butter and sucuk. Optimum growth temp. range from 20-30˚C.Mesophilic starter cultures

Lac. lactis subsp. lactis Lac. lactis subsp. cremorisMesophilic aroma culturesLac.

lactis subsp. lactis biovar diacetylactisLeu. mesenteroides subsp. cremoris

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Thermophilic starter

culturesThey are mainly used for the

production of yogurt, hard cheese and soft cheese. Optimum growth temp. range from 40-45

˚C.Examples:Str. thermophilusLb. bulgaricusLb. helveticus

Lb. lactisLb. caseiLb. acidophilus

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Miscellaneus bacterial starter cultures

Bifidobacterium longumBifidobacterium infantisPropionibacterium shermaniiand they have optiumum

temperature range from 37 C to 41 ˚C.Bifidobacterium ssp.are used as probiotic cultures and Propionibacterium in the production of some type of cheese.

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Types of commercial starter culture

Liquid, for propagation of mother cultureDeep frozen, concentrated cultures for propagation of bulk starter Freeze dried, concentrated cultures in powder form, for propagation of bulk starter culture.Deep superfrozen, superconcentrated

cultures in readily soluble form, for direct inoculation of the product.

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Conditions required

for bacterial fermentationsTemperatureSalt concentrationWater activity

Hydrogen ion concentration(pH)Oxygen avalibiltyNutrients

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Lactococcus

The genus grouped from N group Streptoccus and includes several speciesLac. lactis subsp. lactisLac. lactis

subsp. cremorisLac. lactis subsp. hordniaeLac. garviaeLac. raffinolactis

Thety are ovoid,about 0.5 to 1.0 µm in diameter ,present in pairs or short chains, nonmotile, nonsporulating, homofermentative, facultative anaerobic to microaerophilic and catalase negative. They grow well between 20-30 C,do not grow in 6.5% NaCl and at pH 9.6.In suitable medium they can produce about 1%L(+)-lactic acid and reduce pH to about 4.5.

Natural habitats are green vegetation, silage,dairy environments, and raw milk. They are used in the production of Cottage cheese and white cheeses and butter.

used in dairy fermentation

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Streptococcus

Only one species Str. Thermophilus is used in dairy fermenetation

(such as in yogurt and cheese production)Gram positive,spherical to ovoid,0.7 to 0.9 µ in

diameter,homofermentative,facultative anaerobes and exist in pairs and in long chains.The cells

grow well from 37 to 44 ˚C. But can also grow at 52 ˚ C(

thermoduric),do not grow at 10 ˚ C and in 6.5% NaCl, can reduce pH 4.0

with L(+) lactic acid production.It presentin raw

milk

and

dairy

environment

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Leuconostoc

They are Gr(+),spherical or ovoid ,arranged in pairs or chains, nonmotile, nonsporulating,catalase negative mesophilic. heterofermantative,faculative anaerobes.Grow well 20 to 30 C.Ferment glucose to produce D(-) lactic acid,CO2, ethanol and acetic acid with pH reduction to 5.0-4.5.Leuconostoc

species associates with plants, vegetables,silage,milk,some milk products, and raw and processed meats. One species, Leuconostoc oenos may associate with wine.Example species:

Leu. mesenteroides, Leu.paramesenteroides,Leu. oenos, Leu. galidium.

Leu.

mesenteroides

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Pediococcus

They are spherical and form tetrads, pairs and single cells or forming short and long chains.Gram positive, catalase negative, nonmotile,nonspore forming, microaerophilic and facultative

anerobic.Grow well between 25-32 C.Grow in the presence of 5%NaCl.Ferment glucose to produce L(+) or DL-lactic acid and reducing the pH to about 3.6.The associate with plant, vegetable,silage,beer, milk,fermented vegetables, meats,

and fish.Ped. pentosaceus, Ped. acidilactici and Ped.halophilus are used in vegetable, meal, cereal and other types of fermented food production. The are also responsible in the ripening and flavor production of pickles and sausages.

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Lactobacillus

The genus includes a large number of Gram positive, rod shaped, usually nonmotile, nonsporulating,bcatalase and oxidase negative and facultative anaerobic species.

Dependingg on species they can produce either only lactic acid(L(+),D(-),or DL) or a mixture of lactic acid, acetic acid, ethanol and CO2.Lactobacillus used as starters in controlled fermentation grow well between 25-44 C.pH can be reduced from 3.5 to 5.0.They can associate with plants, vegetables,grains,seeds,raw milk, meat,

fermented meat,and milk products, and fermented vegetables. Some are prsent in digestive tract.The species can be divided into 3 groups1.GroupI-Thermobacterium(Obligately

homofermentative)Ex: Lb. bulgaricus,Lb. lactis,Lb. h

elveticus)2.Group II-Streptobacterium(Facultatively heterofermentative)Ex: Lb.

casei,Lb. plantarum,Lb. curvatus3.GroupIII-Betabacterium(Obligately heterofermentative)

(Ex:

Lb.

fermentum,Lb

.

kefir,Lb

.

sanfirancisco,Lb

.

reuteri

)

Lb.

casei

Lb.

plantarum

Lb.

rhamnasus

Lb.

bulgaricus

Lb.

reuteri

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Bifidobacterium

They are morpholgically similar to Lactobacillus spp. And are previously included in this gnus.They are Gram positive,rods of various shapes and sizes, present in single cells or in chain.They are nonspore

forming,nonmotile,mesophilic,anaerobic and some can tolerate O2 in the presence of CO2.They grow optimally from 37 to 41 C with grow temp. 25-45 C.They usulally do not grow at pH above 8.0 or below 4.5.They ferment glucose to lactic acid and acetic acid in 2:3 molar ratio without production CO2 .They associate in feces of

humans,animals and birds are beneficial for the normal health of the digestive tract. Bifidobacterium called as probiotics are used in the production of fermented milk products such as yogurt,cheese and kefir.They are present in large numbers in the feces of infants within the 2-3 days after birth.Some of the species are Bif. bifidum,Bif

. longum,Bif. İnfantis, and Bif. adolescentia.

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Propionibacterium

They 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.

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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

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Yeast

A 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

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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.

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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.

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Candida

utiis used to produce single cell proteins.They can

cause spoilage in foods.Some candida spp are functional in the

production of kefir, cacao,beer and fruit fermented juices.

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Molds

They 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.

Roquefort

Camemberti

Tempe

Gorgonzola

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Enzymes

Microbial enzymes play a role in the fermentation of food. They are complex proteins produced by living organisms to carry out specific biochemical reactions. They are sensitive to change in temperature, pH, moisture content, ionic strength,

concentrations of substrate and inhibitors.