The Interaction Between Purple Sweet Potato And Lactobacillus In Purple Sweet Potato Lactic Fermentation Broth And Its Process Optimization

In this paper,soymilk and milk are used as fermentation substrates,and different doses of purple sweet potato(PSP)being added using L.rhamnosus or L.plantarum strains to ferment.The mechanism of interaction between PSP fermentation broth and lactobacillus have been studied,including the growth and acid production of lactic acid bacteria in the PSP fermented liquid and effects of lactic acid bacteria on the content of active substances and antioxidant in the fermentation broth of PSP.In addition,the changes of flavor substances in different fermentation broth of PSP during fermentation processing were also studied.Finally,the fermentation parameters of purple sweet potato dairy products were optimized.The experimental results are as follows:1.PSP is added to MRS liquid culture medium,milk culture medium and soymilk culture medium for fermentation with L.rhamnosus or L.plantarum,the results showed that,in each time period,no matter whether fermented with L.rhamnosus or L.plantarum,the number of viable bacteria with PSP was significantly higher(P <0.05)than the medium without it.Acid production capacity has also been improved by adding PSP.Therefore,the addition of PSP can promote the growth and reproduction of lactic acid bacteria,and can accelerate the fermentation process.At the same time,the maximum viable amount of two kinds of lactic acid bacteria in the soybean milk medium without and with the addition of PSP was larger than that of the milk medium,indicating that cheap soybean milk is feasible as a substitute for milk.2.In the milk medium of PSP,scavenging rate of DPPH free radical and ABTS free radical were improved by both kinds of lactic acid bacteria after fermentation.Indicatied that both kinds of lactic acid bacteria could be choosed as fermentation bacteria suitable for PSP milk.In the medium of PSP and soybean milk,the scavenging rate of both DPPH and ABTS and FRAP were improved after L.rhamnosus fermentation.while the antioxidant activity decreases with L.plantarum fermentation.The results showed that L.rhamnosus was a more suitable fermentation strain for PSP soybean milk than L.plantarum.The difference in antioxidant capacity might be related not only to the different substrates of the culture medium,but also to the differences between species.3.The aroma components in the fermentation process of PSP dairy were detected by electronic nose.In soymilk and milk media,although the volatile flavor substances have different sensor response values due to different fermentation strains.The aroma components mainly included sulfides,aromatic constituents,methyl groups,alcohols,aldehydes and ketones,etc.In milk and soybean milk medium,the fermentation flavor of PSP samples was better than that of the blank control.4.The mechanism of interaction between different PSP fermentation broth and lactic acid bacteria showed that L.rhamnosus can be used as the most suitable strain for fermenting PSP milk and PSP soybean milk.Therefore,L.rhamnosus was selected to optimize the process parameters of PSP milk and PSP soybean milk products.The results of single-factor experiments and response surface experiments showed that the fermentation time affecting PSP yogurt was more than the fermentation temperature and inoculation amount;the optimal conditions for PSP yogurt fermentation process were fermentation time 13 h,inoculation amount 0.004%,fermentation temperature 38?.The influencing factors of fermentation time in soybean milk were more than fermentation temperature and inoculums amount.The optimal fermentation process of PSP soybean milk was fermentation time 12 h,inoculum0.003%,and fermentation temperature 41?.