Optimization Of Fermentation Formula And In Vitro Antioxidation Of Mixed Donkey Milk

As a natural food resource,donkey milk has gradually become the focus of development and research because of its rich nutritional components and certain medicinal value.Fermented donkey milk is a kind of donkey dairy product fermented by lactic acid bacteria,which not only has the nutritional value of donkey milk,but also has the probiotic characteristics of lactic acid bacteria,and the fermented donkey milk not only produces some special ingredients,but also improves some physiological functions.Due to the low content of donkey casein,the product fermented with pure donkey milk can not coagulate milk,uneven tissue,layered phenomenon,and the taste is too sour,the degree of acceptability is low.In this study,the mixed fermentation formula of donkey milk was optimized by mixing different amounts of recovered donkey milk and milk,and the mixed fermented donkey milk was made to ensure its nutritional value of donkey milk.it also has good quality and flavor of solidified fermented milk,and the quality and antioxidant capacity of optimized products,fermented donkey milk and fermented milk during fermentation and cold storage were determined.The flavor components of mixed fermented donkey milk were studied by headspace solid phase microextraction(SPME)and gas chromatography-mass spectrometry(GC-MS).The main results are as follows:(1)Formula Optimization of mixed fermented Milk takes the sensory score,viscosity,p H,titration acidity and water holding capacity of mixed fermented milk as indexes,and the optimal range of each single factor is determined by single factor test.The formula of mixed fermented donkey milk was optimized by response surface analysis and sensory score as response value.The best formula was obtained as follows: 27% of recovered donkey milk,5% of sucrose and 1:2 of Lactobacillus plantarum and Lactobacillus helveticus.The sensory and quality analysis of the mixed fermented milk under the optimal formula showed that the sensory score of the mixed fermented milk was 84.17,which was not significantly different from the predicted value of 83.78(P>0.05).The p H value,titration acidity,water holding capacity and viscosity were 4.47,75.9 °T,37.58% and 618.6m Pa s,respectively.(2)Comparison of Fatty acids,Amino acids and volatile components in fermented Milk 16 kinds of amino acids were detected in fermented milk,fermented donkey milk and fermented mixed donkey milk,and the contents of essential amino acids in fermented mixed donkey milk were 1.35 g and 100 g respectively,which were significantly higher than those in fermented donkey milk.A total of 48 volatile components were detected in fermented mixed donkey milk,including 11 esters(5.80%),5 alcohols(2.01%),7 ketones(7.35%),8 acids(62.54%),5 alkanes(5.15%),4 aromatics(5.35%)and 7 others(11.71%).The content of lactic acid in fermented mixed donkey milk was lower than that in fermented donkey milk,and the content of caprylic acid in fermented donkey milk was 24.18%,which was higher than that in fermented milk.In terms of esters,the content of esters in fermented mixed donkey milk was higher than that in fermented donkey milk.among them,butyl propionate and butyl acetate were the highest,which were 1.42% and 1.17%,respectively.The ketone content of fermented mixed donkey milk was 7.35%,which was higher than 0.6% of fermented donkey milk,of which 2-heptanone,2-nonone and3-hydroxy-2-butanone accounted for the main proportion.(3)Study on basic physical and Chemical Indexes and Antioxidant function during fermentation and Cold Storage The changes of p H,acidity,viscosity,water holding capacity and antioxidant activity of fermented milk,fermented donkey milk and fermented mixed donkey milk during fermentation and cold storage were studied.The results showed that with the extension of fermentation,the p H value of fermented mixed donkey milk gradually decreased,viscosity and titration acidity increased gradually,and had good antioxidant activity,and the antioxidant capacity of the three kinds of fermented milk increased during fermentation.The DPPH scavenging rate,hydroxyl radical scavenging rate and superoxide anion scavenging rate of fermented mixed donkey milk were 88.47%,61.54% and 58.42%,respectively,which were higher than those of fermented milk.During cold storage,the viscosity,p H value and titration acidity of mixed fermented milk were higher than those of fermented donkey milk;during cold storage,the antioxidant capacity increased at first and then decreased.The DPPH scavenging rate,hydroxyl radical scavenging rate and superoxide anion scavenging rate of fermented mixed donkey milk reached the maximum on the 6th day of cold storage,which were 92.64%,65.75% and 58.79%,respectively.the antioxidant capacity of mixed fermented milk was higher than that of fermented milk and lower than that of fermented donkey milk.