Production of Hydrolysates from Swordfish ( Xiphias gladius ) Head Muscle as New Protein Source: Evaluation of Nutritional, Antioxidant and Functional Properties

Purpose Fish by-products serve as a major source of protein that can promote the state of health. These by-product wastes have attracted much attention of food biotechnologists due to the availability of large quantities of raw material for the process, and presence of high protein content with good amino acid balance and bioactive peptides. Controlled enzymatic hydrolysis of protein-rich fish wastes is believed to be a better way to produce bioactive peptides. Under this context, this work is to show that swordfish head can be a good source of proteins that can be valorised as functional ingredients. Methods Tow swordfish ( Xiphias gladius ) head muscle protein hydrolysates (XHMPHs) were produced by the separate action of alcalase® (HM-Al) and savinase® (HM-Sa). The physico–chemical characteristics of hydrolysates, such as proximal composition, size, AAs and RP-HPLC profiles, in vitro antioxidant and functional properties were determined. Results XHMPHs showed different degrees of hydrolysis (19.46% with savinase and 11.04% with alcalase). Both hydrolysates had a high protein content (61.82 in HM-Al and 63.61% in HM-Sa) and proportion of small peptides (< 1000 Da) (42.34% in HM-Sa, 38.65% in HM-Al). However, HM-Sa showed the highest content of hydrophobic peptides than HM-Al. In the two hydrolysates, glutamic acid, aspartic acid, arginine and lysine have an individual concentration greater than 5%. Essential amino acids (EAA) accounted for 42% and 39% of the mass of HM-Sa and of HM-Al, respectively. Enzymatic hydrolysis improved solubility at pH values ranged from pH 2.0 to pH 10.0, significantly as well as emulsifying and foaming properties of Swordfish proteins. The emulsifying activity of XHMPHs decreased with increasing concentrations. Conversely, the foaming abilities increased as the hydrolysate concentrations increased. The tow hydrolysates showed dose-dependent antioxidant activities. HM-Sa displayed the highest protection against hydroxyl radical induced oxidation. Conclusions The results suggested that HM-Sa and HM-Al could be used as a source of promising nutritional and pharmaceutical applications. Graphical Abstract