In vitro digestibility and protein digestibility corrected amino acid scores (PDCAAS) were investigated to verify the availability of protein in various Rhizopus oligosporus fermented products of domestic soybean (Glycine max L.) cultivars. Danbaegkong (DBK), Daepung (DP), Daewonkong (DWK), Saedanbaek (SDB), Seonyu (SY), and Cheongja4ho (CJ4) were used as raw samples, which were fermented using commercially available Rhizopus oligosporus for 48 h. All cultivars showed increased crude protein content after fermentation. The crude protein content of DBK and SDB was significantly higher than that of the other samples (55.12% in DBK and 54.22% in SDB) (p<0.001). CJ4 had the highest alanine content of 28.88 mg/g (p<0.001), and no significant difference in cysteine content was detected among the cultivars. In most of the fermented samples, the in vitro digestibility was 0.9 or higher, indicating high protein in the fermented samples. However, it is considered that restrictions on digestion are low. In DWK, the amino acid content and PDCAAS, which together indicate protein quality, were 0.917 and 0.855, respectively, confirming that it was the best cultivar to provide the raw material for fermentation. In conclusion Rhizopus oligosporus fermented soybean products can be considered a prospective source of protein with high utility value.

To analyze the quality characteristics of soybean (Glycine max), the approximate analysis, physical properties, mineral and free sugar content of domestic soybean cultivars were analyzed. The moisture content was about 9.15~11.84%. The fat content of Cheonga, Taekwang, and Jinpung cultivars were 17.93~18.37%, which was significantly higher than that of others. Protein content of Cheonga and Seonyu were 36.15~36.70%, significantly higher than that of others. As for the weight and shape of soybeans, the Daewon was the largest allele, and the seed cover ratio was the highest in the Seonyu. In terms of water absorption rate, the Seonyu showed the highest absorption rate at 246.19%, and the Daewon showed the lowest absorption rate. Soaked soybeans had a hardness of 2.80~4.73 kg/cm2, which did not show low hardness in the sample with high moisture absorption. The grinded soybeans showed higher lightness and yellowness values than the raw soybeans, and the redness was decreased. Soybean minerals contained high K, P, Mg, and Ca content. Overall, The Taekwang contained more minerals than others. Stachyose, sucrose, glucose and fructose were detected as free sugars in soybeans. The total free sugar content of Taekwang was the lowest at 3.47%, and the Cheonga (6.80%) was the highest.