| Soybean products are kinds of nutrient-dense food which are rich in vegetable protein,soybean oligosaccharides,numerous and minerals.However,beany flavor is too unfavorable to be accepted by customers.Studies have shown that microbial fermentation can remove beany flavor and increase aroma of soy products.In this context,our research was aimed at find the suitable starter to apply in food industry.One strain of Pichia amenthionina was isolated from naturally fermented soy whey.And then,their 26 S rDNA sequences and Biolog system microbiological identification results were analyzed.A suitable strain,which had predominant capacity of removing beany flavor,was obtained.Firstly,identification and fermentation performance of isolated strains were studied.A suitable strain,with the name of Pichia amenthionina Y,which had predominant capacity of removing beany flavor,was obtained.It was active in the range of 28~42 ℃ which was well-behaved in temperature resistance.The initial pH value also had an effect on strain,and its optimum pH range is 4 ~ 7,as Pichia amenthionina Y was prefer to live in acidic environment.NaCl content in culture medium also affected the growth of Pichia amenthionina Y.It was active when NaCl concentration was less than 10%.Based on the above fermentation characteristics,it’s known that it’s convenient to select appropriate conditions for Pichia amenthionina Y purebred fermentation as well as mixed fermentation with other strains in practical applications.Secondly,SPME-GC-MS results suggested that n-aldehyde content is up to 35.36%,1-octen-3-ol and 2-pentyfuran were 11.33% and 4.87% respectively in fresh soy milk.After fermentation by Pichia amenthionina Y and Lactobacillus,hexnanl and 2-penthfuran in soy milk were completely removed,other beany flavors’ content were reduced to below 3%,while the formation of 14 kinds of ester aroma components,significantly improved the flavor quality of fermented soybean milk.Fermentation by Pichia amenthionina Y and Lactobacillus also had a positive effect in soy whey.After fermentation,aldehydes and ketones in soy whey disappeared and 21 kinds of ester aroma components were formed.Principal component analysis of volatile flavor components in fermented soy milk and fermented soy whey combined with sensory evaluation results showed that pichia amenthioninaY acted an effective role to remove beany flavor as well as produce ester aroma components.However,fermentation by pichia amenthioninaY was not conducive for the structure of fermented soy milk due to its gas production.Therefore,it’s more suitable to apply pichia amenthioninaY in soy whey instead of soy milk.Finally,apply mixture design to 3 strains fermentation at 42 ℃,the 12-hour fermentation of soy whey,through determination of aroma,taste scores and antioxidant capacity and based on these response values satisfied all expectation were optimized,and the first three excellent combinations were selected.The results of verification tests showed that the optimal formulation has a total expectation of 0.807 for all the indicators,which indicates that the target formula and the predicted value obtained by the experiment are reliable and can be applied to further experimental study.Then,fermentation process of three groups of preferred recipes was analyzed by high performance liquid chromatography.The utilization rate of soybean oligosaccharides and the conversion rate of free soybean isoflavones were higher when fermented by Pichia amenthionina Y and Lactobacillus.Therefore,the first two sets of formulations,namely 2.43% Lactobacillus amylolyticus L6 and 3.57% Pichia amenthionina Y(Formulation 1);1.91% Streptococcus thermophilus ST3 and 4.09% Pichia amenthionina Y(Formulation 2)were suitable to fermente soy whey. |
