Proteolytic degradation and amino acid liberation during extensive hydrolysis of porcine blood hemoglobin by protease admixture

The hydrolysis process of porcine blood hemoglobin by enzyme admixture was characterized for protein degradation, amino acid release and hydrophobicity of recovered hydrolysates with different degrees of hydrolysis (DH) to investigate their relationships with protein recovery (PR) and bitterness. DH increased during the process; however, PR increased with increasing reaction time in the initial phase up to 92.9%, then decreased with increasing time. It means PR was not directly proportional to DH except in the initial phase. Molecular mass of recovered hydrolysates ranged from >15 kDa to free amino acid (FAA) (<1 kDa). The resulting extracted peptides, especially for high molecular weight (>15 kDa) and for containing more hydrophobic amino acids, aggregated and became insoluble during hydrolysis stationary and thus sharply decreased PR. Some FAAs, including methionine, tyrosine, serine and arginine, were likely to contribute to a minor decrease of PR in the test. High average hydrophobic FAA liberation rate in the hydrolysis reduced the hydrophobicity of recovered hydrolysates and possibly decreased the bitterness of the recovery. The hydrophobicity based on Q values and determined by amino acid composition supported Ney's Q rule as a predictor of bitterness for porcine hemoglobin peptides. Porcine blood generated in industrial abattoirs is an abundant by-product that can be used in the food industry at a low cost. Hemoglobin (Hb), the major fraction of blood, is still rarely used in food. This article deals with hydrolysis of Hb by enzyme admixture, which obtained no bitterness of hydrolysate. A complete study of the extensive hydrolysis process, protein degradation and amino acid liberation of Hb is shown. Knowledge about the process may lead to development of new technologies for making nonbitter functional peptides and thus may increase applications of blood protein hydrolysates.