Question

Yoghurt is produced with the help of
(a) Lactobacillus bulgaricus
(b) Lactobacillus thermophilus
(c) Streptococcus thermophilus
(d) Both A and C

Answer 1

Hint: Microorganisms benefit us in a number of ways and we often use products derived from them. Their uses can be distributed into four main categories: commercial, medicinal, agricultural, and environmental.

Complete answer:
- Yogurt is a fermented milk product that contains the specific bacterial cultures namely Lactobacillus bulgaricus and Streptococcus thermophilus.
- The primary (starter) cultures in yogurt are Lactobacillus bulgaricus and Streptococcus thermophilus. The role of the starter cultures is to ferment lactose (milk sugar) to produce lactic acid. Due to the rise in the amount of lactic acid, pH decreases considerably and this causes the milk to clot, and become a soft gel that is characteristic of yogurt. The fermentation pro yoghurt lactose also induces the flavour compounds that are characteristic of yogurt.

Additional information: The various yogurt processing steps are:
- Adjusting milk composition and mixing ingredients: Milk composition is modified to accomplish the desired fat and solids content. Often dry milk is added to increase the proportion of whey protein to give a desirable texture. Stabilizers may also be added at this time.
- Pasteurize milk: Milk is treated at high heat treatment to denature the whey (serum) proteins.
- Homogenize: The mixture is blended to mix all ingredients thoroughly and enhance yoghurt consistency.
- Cool Milk: For the ideal growth temperature of the starter culture, the milk is cooled.
- Inoculate with Starter Cultures: During this stage the starter cultures are added into the cooled milk.
- Hold: At the next stage, milk is held at $108^\circ F$ ($42^\circ C$) until a pH 4.5 is achieved. This gives yoghurt it’s characteristic consistency and taste.
- Cool: The yogurt is then cooled to $7^\circ C$ to cease the fermentation process.
- Add Fruit & Flavours: Different fruits and flavours are added at different steps depending on the type of yogurt.
- Package: The yogurt is then pumped from the fermentation vat and packaged as needed.
So, the correct answer is, ‘(d) Both A and C’.

Note: Additional bacterial cultures, such as Lactobacillus acidophilus, Lactobacillus subsp. Casei, and Bifido-bacteria can also be added to yogurt as probiotic cultures. Probiotic cultures aid human health by enhancing lactose digestion, gastrointestinal function, and stimulating the immune system.