Abstract:

In this research, three spoilage microorganisms named DF-1, DF-2 and DF-3, respectively were separated from
soaked soybeans. Based on their morphological and physiological characteristics, and 16S rDNA analysis, these three strains
were identified as Empedobacter brevis, Enterobacter aerogenes and Lactococcus lactis, respectively. To investigate their
effects on soymilk quality, sterile soymilk was inoculated with each of these spoilage strains and stored at 25 ℃ and changes
in physicochemical indicators were measured during 12 h of storage. Physicochemical properties of soymilk were affected
significantly differently by the three spoilage bacteria. When being cultivated in soymilk, DF-1 produced yellow films with
putrefactive odor on the surface of soymilk while DF-2 produced gas and acid and formed a honeycomb-like gel indicating
spoilage of soymilk. DF-3 also produced acid and caused coagulation of soymilk like yogurt. This research can lay a
foundation for quality and processing stability control of soymilk during automatic production of soybean products.

Key words: soymilk, soaking process, spoilage microorganisms