Introduction:
As implied by the name "lactic cultures," belong to a category of microorganisms that can digest the milk sugar lactose and convert it into lactic acid. For the cells to utilize lactose, deriving carbon and energy from it, they must also possess the enzymes needed to break lactose into two components sugars: glucose and galactose. Some representative strains are Streptococcus lactis, S. cremoris, thermophilus, Lactobacillus bulgaricus, L. acidophilus, and L. plantarum. These
cultures can be purchased directly from local health food and drug stores in tablet form. These tablets, taken orally during the intake of dairy products, help those people who have digestive tract disorder and cannot tolerate lactose. Other than cheese, buttermilk, and yogurt, lactic starter cultures are also used to help prepare or manufacture a wide variety of food products such as sour dough bread, pickles, and sausages. The main (starter) cultures in yogurt are Lactobacillus bulgaricus and Streptococcus thermophilus. The function of the starter cultures is to ferment lactose (milk sugar) to produce
lactic acid. The increase in lactic acid decreases pH and causes the milk to clot, or form the soft gel that is characteristic of yogurt. The fermentation of lactose also produces the flavor compounds that are characteristic of yogurt. Other bacterial cultures, such as Lactobacillus acidophilus, Lactobacillus subsp. casei, and Bifido-bacteria may be added to yogurt as probiotic
cultures. Probiotic cultures benefit human health by improving lactose digestion, gastrointestinal function, and stimulating the immune system (Yogurt Production).
Purpose: To demonstrate the use of microorganisms ( Lactobacillus) in food processing by using
yogurt as an example.
Materials and methods: A. Equipment
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Beakers
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Heat source
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Incubator, Incubator, 43ºC
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Thermometer
B. Reagents
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Milk
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Starter culture (Lactobacillus)
Procedure: First 250 ml of milk was added to 250 ml of beaker and it was then heated
using hot plate till its temperature reached 85 ºC, which was maintained for 2 minutes. The milk was then cooled in water bath till the temperature was 44 ºC after which 1.3 g of yoghurt was added to the cooled milk, and the milk was stirred with glass rod. The beaker was then covered and was incubated at 42 ºC for 3 to 6 hours undisturbed till the desired consistency was reached. Then the yoghurt was placed in refrigerator to stop the growth of the lactic acid culture. Results:
1 litre of milk needs 5 g of yoghurt, so 250 ml of milk will need 1.25 g of yoghurt. The yoghurt formed was having thick and smooth consistency and was white color, set and creamy. Discussion:
The mass of yoghurt added to the milk was more than calculated, this was because there might be some yoghurt left on the weigh boat. The yoghurt formed was having smooth and thick consistency. The yoghurt was creamy, set and was white in color. The characteristics the yoghurt got was due to the temperature at which the starter culture was added and for how much time it was incubated , and what temperature it was incubated.
References & literature cited: Yogurt Production:
http://www.milkfacts.info/Milk%20Processing/Yogurt%20Production.htm
