Selection of microorganisms and optimization of manufacture process for cheonggukjang

This study was conducted to examine the quality enhancement of fermented soybean pastes {cheonggukjang) using microorganisms with high enzyme activities and proper experimental design. The microorganisms for soybean paste fermentation were selected from a specific area of Gyeonggi and were idenlified by 16S rDNA sequence analysis. To prepare the cheonggukjang, an optimum mixing ratio of selected microorganisms was determined using contour plots and numerical optimization methods. A total of 39 microorganisms were isolated from the soybean paste, consisting primarily of Bacillus subtilis and Bacillus licheniformis, and no mold was found. Three microorganisms showing high enzyme activities were selected and used to formulate an optimum mixing ratio for cheonggukjang preparation. Based on levels of amino-nitrogen, ammonium-nitrogen, antioxidant activity values, and sensory preference results, the optimum mixing ratio of 50% of Bacillus sp. SC-1 and 50% SC-3 was suggested for the manufacture of high quality of cheonggukjang.