Screening and identification of amylases-producing strain in sauce-flavor Daqu and optimization of the enzyme-producing conditions

In order to obtain the amylase-producing strain, the strains of amylase production from sauce-flavor (Jiangxiangxing) Daqu was preliminarily screened by iodine staining method and rescreened by enzyme activity determination. The strains were identified by morphological observation and 16S rDNA gene sequence analysis, and the whole genome of the strain was sequenced. Using amylase activity as the evaluation index, the medium components and fermentation conditions of the amylase-producing strain were optimized by single factor and orthogonal tests. The results showed that 9 amylase-producing strains were screened from sauce-flavor Daqu, among which strain L9 had the highest amylase activity (403.25 U/ml). The strain L9 was identified as Bacillus licheniformis, with α-amylase gene and maltose amylase gene in genome. The optimal medium components were as follows: bran 10.0 g/L, tryptone 2.0 g/L, NaCl 0.6 g/L. The optimal fermentation conditions were as follows: fermentation temperature 35 ℃, seed age 8 h, inoculum 3%, liquid loading volume 20%, rotation speed 180 r/min, and fermentation time 33 h. Under those optimized conditions, the amylase activity of B. licheniformis L9 was 2 300.24 U/ml, which was 5.7 times that of before optimization. B. licheniformis L9 had a good ability to decompose soluble starch, which had potential development value and application prospect.