Production and Characterization of Heme Iron Polypeptide from the Blood of Skipjack Tuna (Katsuwonus pelamis) Using Enzymatic Hydrolysis for Food Supplement Application

Organic heme iron in the form of heme iron polypeptide (HIP) is a bioavailable form of iron that can be used for dietary supplements. However, one practical challenge with HIP is that the quality of HIP prepared with different batches of raw material could lead to HIP products with inconsistent characteristics. In this study, skipjack tuna blood, a by-product in canned tuna industry, was converted to HIP at different degrees of enzymatic hydrolysis. The variation in HIP physical–chemical characteristics from different batches was evaluated, including composition, solubility, and molecular weight distribution. It was found that the batch variation had no effect on HIP composition and solubility; however, the degree of hydrolysis (DH) and the size of peptides that interact with heme greatly influenced HIP solubility at pH 2. Tuna-HIP with a low DH (DH, 8%) had 1.76-fold greater solubility than tuna-HIP with a high DH (DH, 32%). High-performance liquid chromatography (HPLC) revealed that tuna-HIP with a low DH had a molecular weight ranging from 1 kDa to 5 kDa. In summary, HIP-derived tuna blood was found to contain 70.54 ± 3.22 mg/100 g of iron and exhibit good solubility at 58.0 ± 2.16% at pH 2. Thus, tuna-HIP with a low DH might be a suitable functional ingredient for iron fortification of food.