This study evaluates the quality properties of soy-paste soybean cultivar for fermented soybean products. The six soybean varieties that include Jinpung, Saedanbaek, Daepung 2, Pyeongwon, Cheonga and Saeolkong were used in the experiment. The range of water uptake ratio, hardness after soaking and hardness after steaming were 117.00~131.33%, 1.65~3.30 kg and 0.05~0.14 kg, respectively. The physicochemical analysis indicated the following: Moisture content, 63.27~68.72%; pH, 6.43~6.60; total acidity, 0.27~0.45%. Color values for L value (lightness), a value (redness), and b value (yellowness) ranged from 39.07~67.92, 7.64~11.79, and 7.48~20.67, respectively. The amylase and protease activities of the Saedanbaek samples were the highest among all cultivars. The amount of viscous substance in the fermented soybean products by cultivars ranged from 5.93 to 8.37%, and Saedanbaek was the highest. The total viable cells counts for soybean fermented products were 9.11~9.42 log CFU/g. The amino-type nitrogen contents of all samples were in the range of 401.07 to 524.47 mg% and Saedanbaek cultivars showed the highest content (524.47 mg%). Based on the results, Saedanbaek will be suitable as a soy-paste soybean cultivar and the quality standards for the fermentation process of the fermented soybean products.

This study was conducted to compare the antioxidant activities of fermented soy products such as chungkukjang, meju and doenjang with soybeans. Total phenolic, flavonoids contents and antioxidative activities of the methanol extract of soy and fermented products were compared with specific reference to alpha-diphenyl-2-picryl-hydrozyl (DPPH) radicals scavenging effects, ferric /reducing power (FRAP), inhibition of conjugated diene formation and tyrosinase activities. Total phenolic and flavonoids contents increased in soybeans after fermentation. Fermented soy products also displayed enhanced antioxidative activities in comparison with the non-fermented soybeans. There were linear relationships between total phenolic and flavonoids contents and ferric reducing/antioxidant power of the samples. Overall, the fermented soy products showed a better antioxidant activity than soybeans. Among the 3 kinds of fermented soy products, chungkukjang, meju and deonjang, doenjang exhibited the highest levels of DPPH-free radicals scavenging activity, ferric /reducing power, inhibition of conjugated diene formation and tyrosinase activities. The fermented soy products with longer fermentation time demonstrated the higher antioxidant activities as well as higher total phenols and flavonoids in the order of doenjang > meju > chunghlkjang> soybeans.