Sequence of Biochemical Change in Milk - PowerPoint Presentation

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Sequence of Biochemical Change in Milk

Prof. Dr. Ir. Sri Kumalaningsih, M.App.Sc

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SEQUENCE In Milk FermentationRaw milk is not free of micro-organisms. The animal may contribute organisms during the formation of milk in the mammary gland, but the greatest source of microoganisms in milk is external fermentation.

A similar comparison can be made with other food products

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Growth Phases and AcidityThe phase represented from A to B is the lag phase which the total numbers of microflora are destroyed or unable to multiplySteptococcus lactic, approximately 0.9% as shown in B-C

The acid restricts the growth of these organisms and then the Lactobacillus group are normally present in the milk, occupies a prominent place, C-D and produce more acid up to 3.5 to 4.0 per cent.

The lactobacillus like the Streptococcus cannot survive in an acid enviroment for a great lenght of time

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They are eliminated in this high acid milk, and the way is paved for typical acid tolerant organisms, molds, and yeasts, as shown in D-E.The molds play an important role in that they can utilize the acid as a source of energy to produce several kinds of basic compounds which tend to neutralize the remaining acidity in the milk.

Preteolytic bacteria become the predominant organisms as represented in E-F.

They cannot survive in an acid medium, hence they must wait until conditions in the milk are favorable for them.

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The Survival of Organisms in Fermented FoodsThe test organisms were destroyed more easily in acidified milk than in milk in which biological acidity was formed

The acidity of fermented milks is not sufficient destroy of pathogenic bacteria. It was found that pathogens survive from 7 to 10 days in acid milk having titratable acidity ranging from 0.95 to 1.20 per cent.

More pathogens survived in the milk when the acidity increased slowly

There was a wide fluctuation in the acidity values of the milk due to variations in the metabolism of the lactic acid bacteria

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Biological and Inherent Acidity and The Survival of MicroorganismsInherent acid in foods tends to d°estroy micro-organisms by creating an unfavourable pH, since most organisms grow very abudantly in a neutral environment or a pH of 7.

The inherent acidity of strawberries and the dissolved sugarwere responsile for the death of S. Typhi within a few hours at room temperature.

Temperature above freezing required a few days and 18, 3°C, very little effect upon the survival organisms was noted

The greatest benefits will be derived if food is handled and processed under strict sanitary conditions.

Washing berries at the patch with unclean water could be a public health hazard

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Fermented Milks

Metchnikoff, in his book, “The Prolongation of Life” describes the therapeutic values of fermented milks, especially acidophilus milk

All of these milks are prepared by growing selected lactic acid organisms as one pure culture or mixture of these organisms

The underlying principle is based upon the ability of the organisms to perpetuate themselves in the intestinal tract

A high protein intake will favor proteolytic organisms

Early scientists believed that toxic by products resulting from the growth of putrefactive bacteria in the intestinal tract were responsible for the so-called “auto-intoxication” or other intestinal disturbances

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Bulgaricus MilkBulgaricus milk resembles cultured buttermilk in most respectsLactobacillus bulgaricus

is the starter organism used in the product

Sterile skim milk is used because of the high temperature of incubation, namely 90°F-100°F (32.2-37.8°C)

This organism often grows in milk with a two to three per cent acid content

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Acidophilus MilkLactobacillus acidophilus is the organism used in the preparation of acidophilus milk and it has the ability to grow in the intestinal tract provided the proper carbohydrates are present

The preparation of acidophilus milk is very difficult, as is that of

L. bulgaricus

milk because the temperature used also favor many other varieties bacteria that are not important in the production

About 1 or 2 per cent inoculum is recommended

Culture carried in skim milk for a short time tend to lose their ability to establish themselves in the intestinal tract

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Yogurt Milk

The product is made from either cow, goat, sheep, or buffalo milk

Preparation of yogurt: Fresh raw milk can be inoculated with an active fermenting batch of yogurt or dried preparation. The milk culture is incubated at 100-1150F (37.8-46.10C) until a thick curd develops or until the titratable acidity reaches sharp acid flavour and distinctive aroma

Yogurt starter: Streptococcus thermophillus and Lactobacillus bulgaricus

Preparaion of Yogurt Milk: the milk batch sterilized much like milk for acidophilus. Usually one per cent of starter organism is added. It incubated at 98.6-100 F (37-37.18 C) for 10-12 hours. The finished product can be place retail containers at 50 F (10 C) until it consumed

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KumissKumiss is a lactic acid fermentation in which Streptococcus lactis and Lactobacillus bulgaricus play an important role.

The native method of inoculation of the milk is the addition of some fermenting or decayed matter, such as apiece of flesh, tendon, or vegetable matter

Lactic acid bacteria and yeast are able to compete with other organisms and thus establish themselves as the predominant microflora in the milk

The temperature of incubation may vary from 24-30,4 C for 12-72 hours

About 1 per cent acid and 2 per cent alcohol are formed during period

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Kefir MilkA preliminary treatment of the culture is necessary in order to get an active fermentation

The culture is ready to be added to fresh pasteurized skim milk and incubated at 21.1-26.6 C for 24 hours until the milk curdles

Lactic acid is formed, ranging 0.5-1.0 per cent; CO2 and alcohol also appear, the latter ranging from 0.3-1.0 per cent after 3-5 days incubation

The fermenting organisms are Streptococcus lactis, Lactobacillus bulgaricus and lactose fermenting yeasts.

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Production and Importance of Lactic Acid Produced in Food by Microorganisms

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Lactic acid or α

hydroxy propionic acid is widely distributed in nature. It occurs in sour milk, beer, bread and in muscle tissue

Any compound to be optically active must have an asymmetric “C” atomm and has one which permits two types of the acid or 3 modifications

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Lactic Acid CulturesThe principal use of starters in the manufacturing of butter, many kind of cheese, cultural buttermilk, and in the production of oleomargarine.

There are three types of streptococci associated in a good butter culture. The organisms are: Streptococcus lactis, S. Citrovorus, or (Leuconostoc citrovorum) and S. Paracitrovorus or (L. Dextranicum)

The associates, sometimes called citric acid fermenters, namely S. Citrovorus and S. Dextranicum are largely responsible for

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The Utilization of Citric AcidThe biochemistry of butter culture is interesting from the stand-point of adding desirable and characteristic flavors to different food products

The general scheme of the breakdown of citric acid by the flavor organisms with the formation of many intermediet product (Hammer and Bable, 1957)

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Cheese Productiongambar

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Cheese ripening is a complex micobiological processThese biological agents are important in the ripening of cheese in addition to the role of starters that he added milkMany varieties of cheese are produce through the action of rennet upon milk.

Differences among varieties are due to many factors such as kind of milk used, amount of moisture retained in the curd, amount of salt added, size of finished cheese, temperature and condition ripening, length of ripening period, kinds of microorganism as starter and general microbial content of the raw milk

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Spoilage of Milk and Dairy Products A natural souring of the milk will take place by Streptococcus lactis and Lactobacillus sp. which is undersirable in market milk.

Gas production by coliform organisms and members of the of the clostridium group is considerable, causing a “stormy fermentation” of milk.

Streptococcus liquefaciens coagulates milk by producing a rennet-like enzyme followed by acid production

Alcaligenes, Pseudomonas, Achroobacter, Micrococcus and Proteus are genera capable of growing at low temperatures and causing proteolysis.

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Streptococcus lactis var. Matigenes is responsible for a cooked or caramel flacour in milk and cream. Pasteurixation will not remove the malt-like flavorRed milk may be due to Serratia marcescens pigment, while Torula glutinis may cause red or pink colonies on the surface os sour cream or milk

Clostridium sporogenes may cause a swelling of the cans in evaporated milk due to gas formation

Bacillus calidolactis, a typical thermohile, may produce similar conditions to those produced by the Clostridium, providing a small amount of air is available in the can.

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Microbiology of SauerkrautThe word sauerkraut means “acid cabbage”In normal cabbage fermentation the process is a spontaneous one in which the bacteria attcak the inherent sugars present in the cabbage and convert them into acids, alcohol and CO2

These oraganisms are frequently referred to as the lacticc acid producing bacteria

Leunostoc mesenteroides is an acid and gas producing coccus

Lactobacillus plantarum and L. Cucumeris are bacilli which produce acid and a very slight amount of gas

Lactobacillus pentoaceticus and L. Brevis are acid and gas producing bacilli