Study On Fermentation Mechanisms Of Lactic Acid Bacteria And Optimization Of Yogurt Technology

On the basis of the present fermentation dairy processing theory and equipment, in combination with the concrete situation of the production in the factory, this paper is to systematically study lactic acid bacteria and fermentation yogurt production technology. The main study contents include: bacteria spawn harvest period and its interaction mechanism; through fermentation test to decide the optimized technology condition; through the study of viscosity to optimize production technology. The research results show that the best harvest period of Streptococcus thermophilus (St) is 6-8 h, and Lactobacillus bulgaricus (Lb) is 12 h. At the moment, the live St bacteria count 1.3×109 cfu/mL, the live Lb bacteria count 9.5×109 cfu/mL. There is an apparent intergrow phenomenon when St and Lb are mixed cultivated. Mixed culture produces acid faster than single culture, and more flavour compounds. In the situation, St mainly produces diacetyl; and Lb mainly produce acetaldehyde; the fermentation acidity must be controlled around 100°T, it tastes best at this moment. Single bacteria spawn fermentation test shows the condition of St fermentation yogurt technology as: temperature 42℃; the inoculation dosage is 3-5%; the total solids are above 11.5%; the condition of Lb fermentation yogurt technology as: temperature 42℃; the amount of inoculumu 3%; the total solids > 11.5%. The result of mixed bacteria spawn fermentation test shows the technology condition as: St : Lb = 1: 1, temperature 42℃, the inoculation dosage is 3%; the total solids are 11.5%; acidity is controlled around 75°T when fermentation finishes. The acidity of the final products after cold storage must be controlled at 90-100°T. Viscosity is an important indicator which influences the quality of fermentation yogurt. Through the study about the viscosity in the production process, it imply that homogeneity pressure must be controlled around 180 kg/cm2; heat treating condition is 95℃, 5 min; stirring should mainly be point-moving; time should be controlled in 1 min. it is best to be cold stored at 5℃ after fermentation and using post-acidification 12-24 h. Through the analysis of every production procedure, 7 HACCP control points have been concluded. The experimental data were proved through the enlargement of the proving experiment. The conclusion of this study can be used to guide the practical production.