Breeding Of The Fermentation Strains From Phage-resistant Yogurt & The Use Of Sugar-free Nutrition Yoghurt

In the recent years, milk related products (MRP) in our country in developing very fast, specially the various kinds of yogurts and the consumption of them. Maintaining and improving the quality of the MRP have become the main problems that we are facing in the principle and practical area. Yogurt is the fermented products from the milk; its quality is strongly related to the quantity of the enzymes that act in fermentation. The main roles of Sour Yogurt (SY) Fermenting Enzymes (SYFE) are:1. Producing acids.2. Producing special tastes.3. Producing glutinous substancesThe quality of the enzymes and the kind of the enzymes play important roles in SY production.The most common enzyme that used in SY production is Streptococins Thermopilos of Lactobacillus bulgaricus. Due to the reaction between the two enzymes, the time taken for producing the SY is shortened and also improves the special taste of it. During the fermentation of the SY, it is easy to be contaminated by phage. This stops the production. Selection of phage-resistant strain to swap the sensitive ones is a way to prevent the damage from phage.This experiment take Lactobacillus bulgaricus and Streptococins Thermopilos as Original Strain, Screens two resistant strain L-12 and S-18. the ultraviolet ray (UV) which is shining from 30cm and illuminating 90s,mutationing and then obtain the L-121015 fungus, it produced the sour ability ratio to embark the strain to enhance 3.4%. Through the 120s mutation with ultraviolet ray, we obtains the S-181124 fungus, it produced the sour ability ratio to embark the strain to enhance 4.8%. Uses the 0.4g/LNTG to process 60min, the L-121015 fungus produces the sour performance comparatively to Original Strain to enhance 7.5%, the S-181124 fungus comparatively Original Strain to enhance 9.1%. Through the union mutation with the ultraviolet ray and the NTG, improve its mutation breeding technology and its production performance, obtains two choiceness phage-resistant mutation strain which is LUN-24 and SUN-23. The acidity of the LUN-24's fermentation product may reach 48.5 oT, viscosity is 135/m?Pa?s-1, acetaldehyde content 88.628ppm; Diacetyl is 58.652ppm.It is higher than primitive Lactobacillus bulgaricus. The acidity of the SUN-23's fermentation product may reach 52.3 oT, viscosity is 121/m?Pa?s-1, acetaldehyde content 16. 125 ppm; Diacetyl is 38. 432ppm. It is higher than primitive Streptococins Thermopilos. After inherits eight generations, the production performance is stable. The breeding strain will use in to manufacture the sugar-free nutrition yogurt. the best fermentation process condition which obtain the sugar-free pumpkin yogurt is: The pumpkin juice and the milk ratio are 1 :1, inoculation capacity is 3%, the yogurt stabilizer is 0.2%, xylitol is 7%, fermentationing for 5 hours, the fermentation temperature is 42℃. In the production, The number of the highest phage is below 10~9pfu/mL.