Research On Fermentation Conditions Of Low-temperature Fermentation And Stirring Type Yogurt

With the improvement of people's living standard,the quality requirements of dairy products are getting higher.Low-temperature fermented yogurt products have a fine taste and good flavor..However,stirred yogurt is affected by fermentation temperature,bacteria type,fermentation time,milk solid content and other factors in the process of low-temperature fermentation.Meanwhile,the low-temperature fermentation time is longer,and the product quality is often not so stability.In this paper,the effects of different fermentation conditions on the quality of stirred yogurt by low-temperature fermentation were studied.And the best bio-protective strains were selected for the development of fermented milk products.Main findings:1.Effect of commercial direct injection fermentation agent on the quality of low temperature and long-term fermentation stirred yogurt.The acidity of the five commercial starters Y450BB,Y480F,Y436A,Y41 and Y170E after fermentation at 30 ? for 18 h were 84 °T,104 °T,84 °T,75°T and 112 °T,respectively.The viscosity and water holding capacity of the yogurt of Y450BB,Y480F,Y41 and Y170E were lower than 2225 mPa s and 68.2%,respectively.The viscosity and water holding capacity of Y436A fermented yogurt were 2750 mPa s and 72.1%.The post-acidification capacity after storage for 3 days at 4 ? was only 3.57%,and the sensory score of fermented yogurt was 98 points.2.Optimization of fermentation conditions for low temperature long-term fermentation stirred yogurt.Based on the acidity,viscosity,water holding capacity and sensory evaluation,the fermentation conditions of the inoculating amount,fermentation temperature and protein content of the low-temperature long-term fermentation stirred yogurt prepared by Y436A starter were optimized by single factor and orthogonal test.The results showed that when adding 9.0%sucrose and 0.25%stabilizer S-031A to the milk containing 3.1%fat,and the content of cow's milk protein is 2.7%,the inoculum of Y436A is 10U/ton,the fermentation time is 32h at 32 ? for 18 h.The long-term fermentation of the stirred yogurt is uniform in color,the aroma of the yogurt is moderate,the sweet and sour is moderate,and the state is fine.The taste is well.3.Study on bioprotective strains of low temperature long-term fermentation stirred yogurt.The effects of six groups of bioprotective strains such as RP80,LPRA,LRB,BG112,YM-C and GP101 on the acidogenic capacity of the fermenting agent Y436A,acidity and sensory quality after yogurt,and inhibition of mold and yeast were studied.The results showed that the addition of 6 groups of bio-protective strains had little effect on the acidity,post-acidification ability and sensory effect of yogurt.The acid lactic acid degree and post-acidification ability of the control group(Y436A)were 82°T and 1.22%,respectively,while the acid lactic acid degree and post-acidification ability of the bioprotective strain were between 82-86 °T and 1.20-2.38%.The sensory score of the yogurt in the control group was 85 points,while the sensory score of the yogurt in the added group of bioprotective strains was between 85 and 88 points.The inhibitory effect of LPRA on mold and yeast in yogurt was better than that of the other five bioprotective strains.The yogurt inoculated with mold began to grow mildew on the second day,and the yogurt added with LPRA began to grow mildew on the fifth day.The yogurt added with other bioprotective strains began to grow mildew on the third or fourth day.The control yogurt inoculated with yeast began to produce gas on the second day,and the yogurt added with RP80 and LPRA began to produce slightly gas on the sixth day.The yogurt added with other bioprotective strains showed gas production on the 5th day.4.Process specifications and standards development and product production.According to the optimal fermentation conditions of low-temperature long-term fermentation and stirring yogurt,the"Technical Regulations for Low-temperature Long-term Fermentation Stirred Yogurt Processing"YDKY-J10.7-2017 and "Fruit Fermented Milk Enterprise Standard" Q/YDKY003-2018.The series of fermented milk,pineapple oat yogurt,strawberry mulberry yogurt and other products have been developed and successfully listed;among them,the series of fermented milk is the company's new sales of 9.64 million RMB from January to August 2018.Compared with conventional short-time fermentation-mixed yogurt,urban regional dairy enterprises produce low-temperature long-term fermentation-mixed yogurt,which can save production cost of nearly 0.6 million RMB per year in terms of labor cost and energy consumption.