Amino acid profiles of kinema, a soybean-fermented food

Abstract

Kinema is an important protein source of traditional Nepalese diets. Total (protein-bound plus free) amino acid profiles of kinema and free amino acid profiles of unfermented and fermented soybeans were determined by reversed-phase high-performance liquid chromatography. Acidic, basic and aromatic amino acids constituted 30.8, 15.1 and 13.0%, respectively, of the total amino acid residues in kinema. The protein component (35.6%, dry weight basis) was rich in all essential amino acids (EAA); EAA7 and EAA10 values (41.7% and 52.6%, respectively, of total protein) were comparable to those of egg and milk proteins. The free amino acid content of unfermented soybeans was only 0.2% of the total dry mass. Processing with Bacillus subtilis led to a 60-fold increase in free amino acid content of soybeans. There was a relative increase in free acidic, hydrophobic and apolar amino acids, but depletion of free basic, hydrophilic and sulphur-containing amino acids. However, the sum of free charged amino acids did not change. Although Enterococcus faecium had no influence, the presence of yeasts significantly reduced the levels of alanine, isoleucine, serine, aspartic acid, asparagine, arginine, tyrosine, methionine and hydroxyproline, suggesting their preferential uptake by the yeasts. On the other hand, amino acid assimilation by yeasts was indicated by the smaller increase in glycine, leucine, glutamine, lysine, histidine, phenylalanine and proline. The fermentation temperature of 45 °C had a significantly adverse effect on free amino acid release.