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Background

In life, people often view yogurt as a kind of flavor drink. It is better in taste and more nutritious than milk, and can better regulate the intestinal flora of the human body. After fermentation, the fatty acids in yogurt increased twice as much as the raw materials. These changes make yogurt easier to digest and absorb, and the availability of various nutrients increases.
In the process of fermentation, lactate acid is one of the most important materials. As a condiment in yogurt processing, it can improve the taste, inhibit the growth of harmful bacteria and enhance the effect of antioxidant[1].
The lactic acid fermentation in yogurt belongs to the I-lactose fermentation mechanism, and the I-lactose fermentation mechanism starts from E. colii. This system is used by many bacteria. Lactobacillus bulgaricus and Streptococcus thermophilus, which are commonly used in yogurt production, also use this system.
The key technology of yogurt processing is the selection of lactobacillus and the control of fermentation temperature and PH value. Lactate acid can improve the quality of yogurt by controlling its PH value.[2] When it is 23 ~ 45 ℃, lactobacillus grow best. It can produce a large amount of lactate acid during the fermentation. It can make the milk acidity up to 3000 T; When it comes to 22 ~ 30 ℃, streptococcus grow best. [3]It can make the milk acidity up to 1000 T.
FIG 1. The process of milk fermentation in yogurt production
Therefore, it is critical to detect the concentration of lactic acid in the process of yogurt production.

Reference

  1. 1.Shengli Yin, Jian Du, Chen Xu, Research status and application of lactic acid bacteria[J]. Food Technology, 2012, 37(9):25—29.
  2. 2.JOHN R P , ANISHA G S, NAMBOOTHIRI K M,et al. Direct lactic acid fermentation; Focus on simultaneous saccharification and lactic acid production[J]. Biotechnology Advance, 2009, 27(2)： 145-152.
  3. 3.Junlin Wu, Jianling Bai, Shuping Mo. Study on fermentation technology of lactic acid bacteria R8 high density process[J]. Modern food Technology, 2018, 34(2):164—170.