Solubility of Heme in Heme-Iron Enriched Bovine Hemoglobin Hydrolysates

A heme-iron enriched peptidic hydrolysate was prepared from bovine hemoglobin, at pilot plant scale, by peptic hydrolysis followed by ultrafiltration. Such preparations are attractive for iron deficiency therapy and have been reported in the literature in the context of utilization of blood in the food industry. The peptidic fraction of this hydrolysate was able to solubilize heme in higher proportion than hemoglobin even at acidic pH where heme is totally insoluble. One peptide, having a similar ability to solubilize heme in the same range of pH, was isolated from this fraction and taken as a model to investigate the mechanisms involved in heme solubilization. Heme seemed to be mainly solubilized through hydrophobic interactions with the peptide, whereas ligancies or electrostatic interaction could not be demonstrated. The stoichiometry of heme−peptide adducts depends on pH with a 2:2 association at pH 2 between heme as a dimer and two peptides and with a 2:1 association at pH 7.5 between one dimer and one single peptide. However, the existence of higher molecular weight aggregates cannot be excluded in the whole hemoglobin hydrolysate. Despite the good solubility of heme and the high heme/protein ratio, such heme enriched peptidic hydrolysates could have a weak bioavailability since heme polymerization is known to decrease heme-iron intestinal absorption. Further studies will be necessary to reduce heme polymerization during enzymatic hydrolysis of bovine hemoglobin.