Decolorization of porcine hemoglobin hydrolysates: The role of peptide characteristics and pH values

The unpleasant color caused by heme limits the utilization of hemoglobin as a food ingredient. Enzymatic hydrolysis has been used to decolorize hemoglobin, but the underlying mechanisms are poorly understood. The aim of this study was to investigate the decolorization efficiency of porcine hemoglobin using different enzymes and final pH values, and to elucidate their influence on decolorization. Based on higher yields and better decolorization, hemoglobin hydrolysates produced by papain, bromelain, savinase, and protease A were further studied. Compared to hydrolysates by savinase and protease A, a higher proportion of histidine-containing peptides was responsible for better decolorization by papain and bromelain. For all hydrolysates, a moderate reduction in pH to 4.0-5.0 facilitated decolorization of the hydrolysates. Similar peptide profiles of hydrolysates from the same enzyme treatment reflected that pH mainly affected the precipitation of the heme-containing fraction through heme-heme interaction rather than heme-peptide interaction. Overall, this study sheds light on the use of enzymatic hydrolysis to remove the heme group from hemoglobin. PRACTICAL APPLICATION: Slaughterhouses produce tons of protein-rich blood each year. Due to the presence of the heme group in hemoglobin, blood has a dark red color and metallic taste, making it generally unacceptable for consumers. This study provided information on the decolorization of porcine hemoglobin by removing the heme fraction, which should facilitate the utilization of decolored hemoglobin hydrolysates as nutritional food ingredients.