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Yogurt is based on fresh milk, inoculated with Lactobacillus under certain conditions Fermented. Yogurt after fermentation, the original portion of the lactose into lactic acid, but still have some lactose, so the formation of a unique sweet and sour flavor, different varieties may be different degrees of fermentation, lactose and lactic acid ratio has a certain difference, so in the taste of some varieties will be sweet, and some varieties will slightly sour.

Lactic acid bacteria[ ] fermentation can be divided into the same type of lactic acid fermentation and special-shaped lactic acid fermentation, the same type of lactic acid fermentation lactose only produces lactic acid, lactic acid fermented lactose in addition to the production of lactate, but also produce ethanol, carbon dioxide and other Substances. In the production of yoghurt, the Bulgarian subspecies (bulgarian lactobacillus) and the thermophilic subspecies of saliva streptococcus (thermophilic streptococcus) are all fermented with lactic acid.[2] Lactic acid fermentation in yogurt belongs to the lactose fermentation mechanism[3,4], the lactose fermentation mechanism is starting from E. coli, many bacteria are used in this system, in yogurt production commonly used in Bulgarian lactobacillus and Thermophilic Streptococcus is also used in this System.

Lactic acid can improve the preservation of yogurt, remove odor odor, increase fragrance, improve the quality of yogurt. It is an important part of yogurt processing, lactic acid bacteria in the processing of yogurt in addition to fermentation and improve nutritional value, but also the following aspects: ① production of lactic acid, ② decomposition of protein, ③ formation of flavor substances, ④ produce antibacterial substances, ⑤ health Effects. (2) yogurt refers to milk as raw material, lactic acid fermentation to make milk protein flocculation into a paste-like products. The lactic acid bacteria producing yogurt mainly include Lactobacillus genus, streptococcus genus and Bifidobacterium genus. Production is commonly used in Bulgaria lactobacillus, Lactobacillus acidophilus, thermophilic streptococcus, streptococcus, bifidobacterium bifidum bifidobacterium, infantile bifidobacterium, bifidobacterium, and so on, the current Chinese yogurt products of the fermentation agents are commonly used in Bulgaria Lactobacillus and Thermophilic Streptococcus strains mixed BACTERIA.[5] The addition of Lactobacillus acidophilus or Bifidobacterium in the fermentation agent can increase the colonization of these two bacteria in the intestine, and further improve the health care effect of Yoghurt.[6]
In addition, lactic acid also plays an important role in the alcoholic fermentation industry.
the content of lactic acid in the fermentation industry is closely related to the quality of fermented products. We will examine the effects of these substances on yeast growth and alcohol fermentation. In the medium, containing a small amount of acetic acid, lactic acid, caramel pigment and furfural will have a serious inhibitory effect on the growth and reproduction of yeast, the inhibition intensity is acetic acid, and then the furfural, caramel pigment. Acetic acid has the strongest effect on the growth inhibition of yeast, which is very difficult to grow when the content of acetic acid in medium is 0.13. When the number of yeast cells decreased by 50%, the added amount of acetic acid, lactic acid, caramel pigment and furfural were 0.1%, 0.1%, 2% and 0.2% respectively. [9]Adding four substances of the above concentration to the medium simultaneously has a stronger inhibitory effect on the growth of yeast, and its inhibitory strength is up to 70%.
To better control the concentration of lactic acid, we plan to construct a fluorescent protein sensing circuit to monitor the alcohol concentration in the fermentation industry in real time. We will use the system of Escherichia coli to induce alcohol concentration. First, we will use plasmid pCDFuet-1 as a carrier to construct an expression plasmid that can detect alcohol concentration and release K12 strain. [7]The K12 strain can trigger another plasmid pet28a expressing fluorescent protein. [8]In the end, we will monitor the fluorescence intensity in real time with the sensitive circuit.

Reference

  2. Shengli Yin, Jian Du, Chen Xu, Research status and application of lactic acid bacteria[J]. Food Technology, 2012, 37(9):25—29.
  3. 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.
  4. 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.
  5. Qingjun Meng, Wenhong Feng, Gang Fu. Application of glucose and lactic acid biosensor in the process of maize soaking[C]// The first Chinese enzyme engineering symposium..Guangzhou:[s.n.]2011.
  6. Mannheim bochringer; 《methods of Enzymatic Food Analysis》,(1986)
  7. Volfgang et al. ; Appl. MICROBIOL.Biotechnol.,34:573~578（1991）
  8. De Keersmaecker SC, Sonck K, Vanderleyden J. Let LuxS speak up in AI-2 signaling. Trends Microbiol 2006; 14:114119.
  9. Li J, Attila C, Wang L, et al. Quorum sensing in Escherichia coli is signaled by AI-2/LsrR: effects on small RNA and biofilm architecture. J Bacteriol 2007; 189:6011-6020.
  10. B.Maiorrella, G. Blanch, and C. Wilk,” By—product inhibition Effects on Ethanolic Fermentation by Sacharomyces cerecsiae”, Biotechnol[J]. Bioeng.1983,(125): 1—4.