Study On Fermented Potato By Lactic Acid Bacteria And High-density Culture

In this study,three lactic acid bacteria used as experimental strains were Lactobacillus plantarum299 and Streptococcus thermophiles 176.By optimizing the fermentation process,we developed lactic acid bacteria fermentation potato beverage.And to adapt to industrial production,high-density culture of Streptococcus thermophilus176 were studied.The main contents and results are as follows:(1)After the determination of the basic components of the potato,the single factor experiments of potato raw material compound and fermentation conditions were carried out.The optimum conditions of lactic acid fermentation of potato were determined by the further optimization experiment of the response surface.The optimum conditions for the fermentation of potato by lactic acid bacteria were potato:water=1:1,sugar concentration 4.8%,milk concentration 10%,sterilization condition 80?,10 min,Lactobacillus plantarum299:Streptococcus thermophiles=2:1,inoculation 1.8×108 cfu/mL,fermentation time 8 h,temperature 37?.The product made in this condition was appetitive and delicious,and it tasted mellow and delicate.The potato lactic acid bacteria beverage made under the optimum conditions was preserved at 4?.(2)Lactic acid fermentation of the potato will produce many kinds of compounds which will have an impact on the taste and flavor of the product.Therefore,the types and contents of organic acids and volatile flavor substances before and after fermentation of potato lactic acid bacteria were determined by HPLC and GC/MS.It was found that the content of lactic acid,malic acid and citric acid in the post-fermented significantly increased and acetic acid content decreased,which helped to slow down the irritating odor of acetic acid and improve the sour to make it softer.Flavor substances are mainly esters,aldehydes,alcohols,ketones,furan and hydrocarbons and other compounds.A total of 36 components were detected before fermentation and a total of 64 components were detected after fermentation,which improved the flavor of the beverage and maked it softer.Streptococcus thermophilus176 starter existed the shortcomings of less biomass and low viable count so that it can not achieve the industrial production of the product.Therefore,The factors influencing the high-density culture,such as fermentation temperature,stirring speed,fermentation pH and neutralizing agent,were optimized on 7 L semi-automatic fermentation tank.The results showed that the best high-density culture conditions were:fermentation temperature 37?,stirring speed 100 r/min,neutralizer 25%ammonia,fermentation constant pH 6.0.The OD600 of the fermentation broth could reach about 0.8,which was about 1.7 times higher than that of the common fermentation.After optimization,the final powder of Streptococcus thermophilus 176 viable count of 3.15 ×1011cfu/g.