Degradation characteristics of proteins in cheonggukjang (fermented unsalted soybean paste) prepared with various soybean cultivars

In order to select the most ideal soybean cultivars for producing cheonggukjang, the protein degradation characteristics of cheonggukjangs prepared with 30 different soybean cultivars were compared. Cheonggukjang prepared with 'Nampung' (18. 00±0. 28%) and 'Sohwang' (17. 91±0. 63%) soybeans showed the highest contents of viscous substances. Acidic-protease activity was highest (590. 24±2. 92 μg/mL) in cheonggukjang prepared with small 'Pungsannalmul' soybeans. Neutral-protease activity was highest (528. 13±3. 11 and 527. 36±0. 44 μg/mL, respectively) in cheonggukjang prepared with 'Singi' and 'Nampung' soybeans. Cheonggukjang prepared with 'Wonkwang' and 'Sohwang' soybeans had amino-type nitrogen contents of 780. 50±2. 92 and 729. 95±1. 07 mg%, respectively. Glutamic acid, which is a major component of viscous substances, was also detected. Although total free amino acid levels in cheonggukjang prepared with 'Daewon' and 'Wonkwang' soybeans measured 2,551. 21 and 2,340. 02 mg%, respectively, cheonggukjang prepared with black soybeans exhibited low levels of total free amino acids. Therefore, based on protein degradation characteristics, large 'Daewon' soybeans and small 'Wonkwang' soybeans were the most suitable for producing cheonggukjang.