Study On The Key Preparation Technology And Application Of Potato Blueberry Yogurt

Potatoes and blueberries are the characteristic agricultural products of Guizhou Province,which are rich in nutrition and have a wide planting area.At present,there are many studies on the fermentation of yogurt with potato or blueberry as raw materials,but there is no research on the fermentation of yogurt with potato and blueberry.Meanwhile,in the aspect of yogurt starter,there are few excellent commercial strains with independent intellectual property rights in China,and the preparation technology is relatively backward.To solve the above problems,this paper optimized the protective agent of the laboratory self-screening probiotics in the vacuum freeze-drying process to obtain the lyophilized and concentrated starter with high survival rate.A new functional flavor yogurt with potato and blueberry as raw materials was produced by self-made starter culture and the nutritional composition of the yogurt with potato and blueberry was improved by adding perilla seed oil.The aim is to increase the market share of starter culture,promote the deep processing of potato and blueberry,and broaden the types of functional flavor yogurt.Specific research contents and results are as follows:(1)Single factor and response surface(Response surface experiment:RSM)experiments were used to determine the optimal combination of protective agents for self-screening probiotics during vacuum freeze drying.The optimal combination of protective agent for Bifidobacterium animalis subsp.lactis(BZ11)was 15.51%trehalose,10.44%skim milk powder and 3.70%sodium glutamate.The optimal combination of protective agent for commercial Streptococcus thermophilus(Q-1)was 11.09%trehalose,10.21%skim milk powder and 3.44%sodium glutamate.The optimal combination of protectant of Lactobacillus plantarum(LB12)was 10.13%trehalose,4.26%sodium glutamate and 10.35%skim milk powder.The survival rates under optimal protectant were 92.87±1.25%(BZ11),81.1±1.06%(Q-1)and83.65±1.22%(LB12),respectively,which were increased by 19 times(BZ11),22times(Q-1)and 6 times(LB12)compared with those without the addition of protectant.Meanwhile,there was no significant difference in cholesterol clearance rate,pH value,sensory and viable count of fermented yogurt whether the strain was freeze-dried or not.In addition,the combined fermentation of BZ11,LB12 and Q-1could produce a good flavor yogurt with low cholesterol.(2)Taking sensory score,pH and anthocyanin as indexes,the optimal fermentation parameters of potato blueberry yogurt were obtained by single factor,Plackett Burman(PB)and RSM experiments as follows:potato juice 33%,blueberry juice 22%,fermentation temperature 38?,sucrose 3.7%,skim milk powder 14%,inoculation amount 4%,strain ratio(BZ11:LB12:Q-1)1:1:2,fermentation time 12.5h.Under these conditions,the sensory score of potato blueberry yogurt was89.78±1.69,the pH value was 4.47±0.03,the anthocyanin content was 9.41±0.10mg/100g,and the viable bacteria count was 9.31±0.03 log CFU/m L.In the fermentation process,correlation analysis showed that there were significant correlations among fermentation time,anthocyanin content,pH value,soluble solid content,L~*value,a~*value and viable bacteria count.(3)Based on the optimal fermentation technology,the effects of perilla seed oil on yogurt were studied.The results showed that perilla seed oil decreased the sensory score and acid production rate of yogurt,and improved the water-holding capacity and antioxidant capacity of yogurt;High concentration perilla seed oil had inhibitory effect on microorganisms,but low concentration had promoting effect on microorganisms.Perilla seed oil had different effects on different types of organic acids,and significantly reduced the contents of citric acid,tartaric acid,succinic acid,lactic acid,acetic acid and malic acid,but had no effect on the contents of oxalic acid,formic acid and propionic acid.During storage,the higher the content of perilla seed oil,the faster the sensory and pH decreased,but the pH reduction rate of 1%samples was lower than that of 0%samples.At the end of the storage period,only 0%and 1%perilla seed oil potato blueberry yogurt with sensory score higher than 75,but 1% perilla seed oil can reduce the loss of fermentation strains during storage.Therefore,the most appropriate addition amount of perilla seed oil is 1%.Although perilla seed oil reduced the variety of fatty acids of yogurt,it increased the proportion of polyunsaturated fatty acids and reduced the?-6/?-3 ratio to a reasonable range of2-4:1.(4)Headspace solid phase microextraction-gas chromatography-mass spectrometry(HS-SPME-GC-MS)was used to study the flavor components.The results showed that the main flavor substances of fermented yogurt were acids,aldehydes,ketones and alcohols,regardless of whether perilla seed oil was added.However,their relative contents were different.The addition of perilla seed oil increased the relative content of aldehydes and ketones,and increased the variety of yogurt flavor substances.The free amino acid level of perilla seed oil potato blueberry yogurt(48.4mg/100g)was higher than that of potato blueberry yogurt(47.2mg/100g)by automatic amino acid analyzer.In addition,the number of bifidobacteria and total viable bacteria in perilla seed oil potato blueberry yogurt was significantly higher than that in potato blueberry yogurt,and the sensory score was as high as 83 points,indicating good acceptability.Compared with the commercial yogurt,the perilla seed oil potato blueberry yogurt also has some outstanding advantages,such as low total sugar content,high number of viable bacteria and far higher number of bifidobacteria than the recommended value.These results can provide data support for the industrial application of starter culture and the development of dairy products.