关键词: 豆酱, 蛋白质, 氨基氮, 氨基酸, 呈味氨基酸

Abstract: In order to study the changes and evaluation of protein and amino acids in the natural fermented soybean pastes from different fermentation period, the natural fermented soybean pastes from the northeast China was collected during different fermentation period. After the determination of protein, amino nitrogen, non-protein nitrogen and hydrolysis index, the amino acid content were measured by the L-8800 automatic amino acid analyzer, followed by analysis of amino acid score (AAS), chemical score (CS) and essential amino acid index (ENNI). The results showed that, the protein content, non-protein nitrogen content, proteolysis index of soybean pastes were increased at first and then decreased, but amino nitrogen content was increased until stable. 17 kinds of amino acids excluding tryptophan (Trp) because of hydrolysis were measured in the natural fermented soybean pastes. However, with the fermentation, the content of amino acids was extremely different. The total content of amino acids on 20d was 69.65mg/g at most, while the total amino acids on 5d was 39.03mg/g at least, the amount of amino acids of the ripe soybean pastes remained at around 41.00 mg/g, which was higher than the raw soybean flour (11.424 mg/g) and cooked flour (11.06 mg/g) significantly. The ratio of essential amino acids and non-essential amino acids (E/N) were changed from 0.50 to 0.77, which proved that soybean pastes contain high quality protein. Based on analysis of AAS, CS and ENNI, the EAAI was reached the highest value at 29.41 on 20d. then was decreased from 16.16 to 17.40 during 50 to 75d. By comparing four kinds of flavor amino acid, the content of sweet amino acid was the most, followed by bitter amino acids then umami amino acid, tasteless amino acids was the least.

Key words: soybean paste, protein, amino nitrogen, amino acid, taste-active amino acids