| Traditional natural fermented old sauce of Bai nationality in Yunnan Province has its unique flavor and is deeply loved by local people.However,traditional natural fermented sauce is the main method,which has some problems such as long fermentation time and unstable product quality.In this paper,the traditional natural fermented soybean paste of Bai nationality in Yunnan was taken as the research object and the change of physicochemical index of the traditional raw material of fermented soybean paste was analyzed.Besides,GC-IMS was used to determine its volatile flavor substances and the quality index of fermented mature soybean paste was explored,which provided certain theoretical basis for the production of fermented soybean paste.The superior microorganisms producing protease and amylase from traditional fermented old sauce were screened for inoculation and fermentation,the fermentation process was optimized,the optimum production conditions of old sauce were determined and the quality analysis was carried out.The main findings are as follows:(1)To explore the changes of physical and chemical indexes in the fermentation stage of pastry.After fermentation,the moisture content reached 35.665%,the p H value was6.715,the total acid content was 0.24 mg/g,and the amino acid nitrogen content reached0.0945 g/100 g.The contents of reducing sugar and total sugar were 95.93 mg/g and 277.46mg/g,respectively.(2)A total of 78 kinds of volatile flavor substances were detected by GC-IMS,including 16 kinds of aldehydes,21 kinds of esters,12 kinds of alcohols and 8 kinds of ketones.The concentration of volatile compounds in the fermented flour cake increased significantly,including 2-pentanone,4-isopropyl benzyl alcohol,2-hexanol,isoamyl alcohol,3-methyl-3-butene-1-alcohol,(E)-2-heptenal,which showed the unique flavor of the flour cake.At the same time,the volatile flavor compounds of the flour cake before and after fermentation were well clustered.(3)After the isolation and purification of the dominant strains in Bacillus licheniformis,three strains with good performance were obtained.Physiological and biochemical analysis and molecular biological identification were performed on the strains,and phylogenetic tree was constructed.The results showed that strain D1 was Bacillus Licheniformis.Strain D2 was Bacillus amyloliquefaciens and strain F3 was Bacillus subtilis.(4)For the fermentation conditions of old paste in the pre-fermentation stage,the process was optimized by single factor and response surface experiment,and amino acid nitrogen was used as the index.The optimal fermentation conditions were obtained as follows: flour supplemental level was 14.69%,sugar supplemental level was 4.55%,salt supplemental level was 6%,strain compounding ratio was VD1: VD2: VF3=2:1:1,inoculation amount 2%,fermentation temperature 37 ℃,fermentation time 5.5 days.Under optimal conditions,the content of amino acid nitrogen reached 0.1474 g/100 g and the sensory score was 88 points.(5)The physical and chemical indexes of the optimized old sauce were determined.During the first 10 days of fermentation,the p H of the old sauce gradually decreased,and the contents of total acid and amino acid nitrogen gradually increased.Finally,the total acid content was 4.77 mg/g and the maximum of amino acid nitrogen was 0.166 g/100 g.According to various quality indexes(reducing sugar,total sugar,amino acid nitrogen),the old paste with optimized inoculation technology is better than the old paste without inoculation. |
