Selection Of Functional Lactic Acid Bacteria And Their Applications In Low-salt Solid-state Soy Sauce Fermentation

Low-salt solid-state（LSSS）soy sauce is specialized for its strong sauce flavor and nice result in tinting food materials.It is widely used in cooking and food processing.However,low-salt solid-state soy sauce is deficient in color style and flavor due to fermentation at high temperature for a short time.Optimization of raw material composition and fermentation process limitedly improve the flavor and quality of LSSS soy sauce.Thus,study on functional bacteria and their effect on LSSS soy sauce fermentation is of great significance for selection of functional microorganisms to improve the flavor and quality of LSSS soy sauce.In this study,functional bacteria that could adapt to LSSS soy sauce fermentation conditions were isolated from the moromi.The effect of adding functional bacteria on physicochemical properties,quality and flavor of LSSS soy sauce were investigated.These would provide references for improvement of the quality and flavor of LSSS soy sauce by synergetic fermentation with functional bacteria.The main research results were as follows:（1）The differences in quality and flavor between LSSS and high-salt liquid-state（HSLS）soy sauce was preliminarily revealed.The total volatiles in LSSS soy sauce was 48.81%,which was lower than that in HSLS soy sauce.The main volatiles such as 1-octene-3-alcohol and 4-ethyl guaiacol were 72.27%and 91.88%lower in LSSS soy sauce than those in HSLS soy sauce,respectively.The red and yellow indexes of LSSS soy sauce were 6.19%and 2.54%lower than that of the HSLS soy sauce.（2）A lactic acid bacterium P.acidilactici WT1 that could be used for LSSS soy sauce fermentation was obtained.The bacterial composition of moromi during LSSS soy sauce fermentation was analyzed.And 35 bacterial strains were isolated from the moromi.Among them,P.acidilactici WT1 exhibited better growth at 45°C or in the presence of 8%salt.It produces organic acids(30.22 g·L^-1)and amino acids(3.06 g·L^-1)at the highest level.P.acidilactici WT1 also has good capability in inhibition of the spoilage bacteria Enterobacter.（3）The quality and flavor of LSSS soy sauce were improved by P.acidilactici WT1through synergetic fermentation.The contents of amino acid nitrogen,red and yellow indexes and succinic acid in P.acidilactici WT1 synergistically fermented soy sauce were increased by9.43%,8.87%,6.19%and 71.87%.In addition,the umami and sweet amino acids contents were increased by 35.16%and 13.44%,respectively.The total amount of volatiles was increased by19.95%.The main volatiles in soy sauce guaiacol and phenol,were increased by 35.49%and50.64%,respectively.（4）Optimization of fermentation process of P.acidilactici WT1 synergistically fermented soy sauce.By optimizing the inoculation size,salt contents and fermentation temperature,the content of volatiles in P.acidilactici WT1 synergistically fermented soy sauce was significantly increased.The contents of succinic acid,free amino acids and isoamyl alcohol in soy sauce inoculated with 10⁸CFU·g^-1 P.acidilactici WT1 increased by 49.12%,27.64%and 42.7%,compared with 10⁶CFU·g^-1,respectively.Addition of 8%salt for fermenation,the content of volatiles in soy sauce was 12.10%higher than that in 4%salt fermented soy sauce.After optimization of fermentation temperature（40°C for 5 days and 45°C for 20 days）,the red index and yellow index of soy sauce were significantly increased,and the contents of 2,4-di-tert-butylphenol were 7.51 times higher than those in the soy sauce fermented under the original condition（starting at 40°C and heating up at 1°C/day to 42°C,and 45°C for 22 days）.