Study On Fermentation Of Soybean Paste With Compound Strain

Soybean paste is one of the traditional fermented bean products in China,and which key steps of production process are koji-making and fermentation.The enzyme system and enzyme activity of the koji directly affect raw material utilization rate and the fermentation period,and the aroma components of the soybean paste are mainly produced in the fermentation stage,and it's popular that koji-making and fermentation using multi-strains via artificial inoculation in recent years.So in this paper,the study of complex-strain koji-making and fermentation based on the enzyme production and enzyme activity of the strains,then the fermentation process was further optimized and obtained the soybean paste with high amino nitrogen content and total ester content.The main findings are as follows:In the koji-making process,the best enzyme production time of Aspergillus oryzae Huniang 3.042,Aspergillus batatae AS 3.324,Mucor Huniang 3.130,Monascus AS 3.972,Rhizopus oryzae and Bacillus subtilis strains were 72 h,and the best enzyme production time of Aspergillus niger AS 3.35 was 48 h.The protease activity of Aspergillus oryzae was the highest,followed by Bacillus subtilis,Aspergillus batatae,Monascus,Aspergillus niger,Mucor,and Rhizopus oryzae;the amylase activity of Aspergillus batatae was the highest,followed by Aspergillus niger,Aspergillus oryzae,Monascus,Mucor,Bacillus subtilis,and Rhizopus oryzae;the glucoamylase activity of Aspergillus niger was the highest,followed by Aspergillus oryzae,Aspergillus batatae,Monascus,Mucor,Rhizopus oryzae and Bacillus subtilis.Single-strain koji-making and fermentation,koji-making and compound strain fermentation,and compound strain koji-making and fermentation were comparatively studied.The pre-fermentation time was determined as 7 days because the amino nitrogen content of soybean paste exceeded the specified standard after 7 days of single-strain koji-making and fermentation,and sample No.1 had the highest protease activity and amino nitrogen content.Two kinds of fermentation methods for koji-making and compound strain fermentation and compound strain koji-making and fermentation,the 3 strains produced higher protease activity and amino nitrogen content,among which 3-5th produced highest protease activity and amino nitrogen content.Among the three koji-making and fermentation methods,koji-making and compound strain fermentation produced highest protease activity and amino nitrogen content and is more suitable for soybean paste.The 3-5th of Aspergillus oryzae Huniang 3.042,Aspergillus niger AS3.35 and Bacillus subtilis koji are fermented according to 1: 2: 1 ratio,the protease activity and amino nitrogen content of soybean pasta are optimal.After the pre-fermentation,soybean paste inoculated the Lactobacillus plantarum and Zygosaccharomyces rouxii AS 2.180 to ferment.The response surface methodology was designed using the Box-behnken method,and combined with the actual situation,soybean paste prepared under salt concentration of 12%,fermentation time of 34 days,ratio of complex strain inoculation of 8: 1,and combined strain inoculation of 1.0% had an amino nitrogen content of 1.43 g/100 g and total esters content of 0.71 g/L,and compared with single-strain koji-making and fermented soybean paste,compound strain koji-making and fermented soybean paste,traditional natural fermented soybean paste and commercial soybean paste,it had the highest amino nitrogen content,total ester content,total acid content score,and sensory scores was close to commercially soybean paste.