豆酱自然发酵过程中蛋白质和氨基酸的变化规律

为研究豆酱在自然发酵过程中蛋白质、氨基酸组成及含量的变化规律,以按照东北豆酱传统方法制作的自然发酵豆酱为研究对象,在检测蛋白质含量、氨基氮含量、氨基酸含量、非蛋白氮含量和水解指数等指标变化的基础上,对豆酱的氨基酸评分(amino acid score,AAS)、化学评分(chemical score,CS)、必需氨基酸指数(essential amino acid index,EAAI)进行分析。结果表明,豆酱蛋白质含量、非蛋白氮含量、蛋白水解指数先上升后下降;氨基氮含量则先不断增加后减少至稳定。自然发酵豆酱中共含有17种氨基酸,但不同发酵时期豆酱中氨基酸含量差异较大,成品豆酱中氨基酸总量维持在41.00 mg/g左右,明显高于生豆粉(11.42 mg/g)和熟豆粉(11.06 mg/g)中氨基酸总量。不同发酵时期豆酱中必需氨基酸与非必需氨基酸的比值在0.48~0.77之间,提示豆酱中的蛋白质为优质蛋白。分析不同发酵时期豆酱的AAS、CS和EAAI可知,发酵20 d时EAAI最高达29.41,发酵50~75 d豆酱的EAAI保持在16.16~17.40之间。通过比较4种呈味氨基酸的含量可知,甜味氨基酸苦味氨基酸鲜味氨基酸无味氨基酸。

Evaluation of Changes in Protein and Amino Acids in Naturally Fermented Soybean Pastes with Different Fermentation Periods

Naturally fermented soybean pastes were prepared by the same method as that for traditional fermented soybean paste in northeast China with different fermentation periods, and they were investigated for changes in protein content and amino acid composition during the fermentation. In addition to the contents of protein, amino nitrogen, amino acids and non-protein nitrogen and hydrolysis index, amino acid score (AAS), chemical score (CS) and essential amino acid index (EAAI) were also analyzed. The results showed that the content of protein, non-protein nitrogen, and proteolysis index of soybean pastes were increased at first and then decreased, but amino nitrogen content was increased until reaching a plateau. A total of 17 kinds of amino acids were measured in the naturally fermented soybean pastes. It turned out that, with the fermentation, the contents of different amino acids were extremely different. The total amount of amino acids in the ripen soybean pastes remained at around 41.00 mg/g, which was significantly higher than that of raw soybean flour (11.42 mg/g) and cooked flour (11.06 mg/g). The ratio of essential amino acids to non-essential amino acids (E/N) was changed from 0.48 to 0.77, which proved that the soybean pastes contained high quality protein. Based on analysis of AAS, CS and EAAI, the EAAI reached the highest value of 29.41 on day 20 of fermentation and then was decreased to a stable level in the range from 16.16 to 17.40 during day 50 to 75. The contents of different taste-active amino acids were in the order of sweet amino acid > bitter amino acid > umami amino acid > tasteless amino acid.