1 Briefly describe the physical and mechanical processes inv

1) Briefly describe the physical and mechanical processes involved in the production of yogurt.

2) What is fermented milk product? How can one tell that fermentation has occurred? What organisms are employed in the production of fermented milk products?

3) What would happen to a yogurt preparation if a 2% gelatin solution was added to it?

Solution

1. The first step in the production of yoghurt is to increase the amounts of solids in milk excluding fats. The solid content of milk is increased from 1.5% to 16%. The milk is then pasteurized and homogenized, to kill all previous microbes and disperse the fat globules respectively. At this stage the milk is more viscous and has a smoother texture.

The milk is brought to tempratures around 109.4-114.8° F (43-46° C) and fermentation culture is added. The bacteria in this culture mostly include Streptococcus salivarius and Lactobacillus delbrueckii, among other bacteria ( Lactobacillus bulgaricus and Streptococcus thermophilus must be present in all yogurts under US law). These bacteria are lactic acid bacteria, and use lactic acid fermentation to convert the hexose sugars in the milk to lactic acid. This results in a sour taste, a decrease in pH and a congealated paste like consistency. This change in the form from a liquid to a mesh like solid holding the liquid is caused due to the pH dropping below the isoelectric point of casein, which cross-links with transglutaminase.

2. Fermented milk products are those which have been fermented using lactic acid bacteria. The landmark sign of fermentation is the production of lactic acid, which turns the milk sour. The viscosity of the milk also changes. Lactobacillus, Leuconostoc, Pediococcus, Lactococcus, and Streptococcus are the major groups associated with fermentation of milk.

3. Addition of gelatin will increase the viscosity and thickness of the yoghurt, and can improve the texture.