?-Caseinophosphopeptide (f1-25) confers on ?-casein tryptic hydrolysate an antioxidant activity during iron/ascorbate-induced oxidation of liposomes

Abstract

Protein ingredients such as hydrolysates of milk proteins may improve the nutritive value of functional foods. For instance, β-casein tryptic hydrolysate could simultaneously increase iron absorption and prevent lipid oxidation in foods containing high contents of polyunsaturated fatty acids (PUFA). The aim of this study was to determine the antioxidant activity of β-casein tryp- tic hydrolysate and of its β-caseinophosphopeptide (f1-25) on Fe(III)/ascorbate-induced oxidation of muscle phospholipids in a liposome system. Oxygen consumption, conjugated dienes (CD), thio- barbituric acid reactive substances (TBARS) and volatile compounds were measured during oxida- tion at 25 °C of the liposomes in the presence of either the β-casein tryptic hydrolysate (0.24- 2.4 mg·mL-1) or of its phosphopeptide (0.1-0.31 mg·mL-1). Oxygen consumption was signifi- cantly enhanced in the presence of β-casein tryptic hydrolysate or of the phosphopeptide (f1-25) and staircase curves were observed for the highest concentrations, showing complex oxidative interac- tions between iron, β-casein tryptic hydrolysate or phosphopeptide and the phospholipids. In con- trast, on an hourly scale, formation of CD, TBARS and total volatile compounds were inhibited. The inhibition of CD and TBARS reached 50% after 20 h of oxidation in the presence of 1.2 mg·mL-1 β-casein tryptic hydrolysate or 0.16 mg·mL-1 phosphopeptide (f1-25). Amounts of total volatile compounds produced after 24 h decreased by about 60% in the presence of the hydrolysate (1.2 mg·mL -1 ) and 50% with the phosphopeptide (f1-25) (0.31 mg·mL -1 ) due to drastic decrease or even disappearance of alkanals and 2-alkenals. Several alcohols such as pentanol and hexanol were produced in higher amounts. Thus β-casein tryptic hydrolysate can protect rich-in-PUFA phospho- lipid liposomes against long-term iron-induced oxidation, mainly due to iron chelation by β-casei- nophosphopeptide (f1-25). This antioxidant activity could benefit specific food products. Antioxidant activity / milk protein hydrolysate / phosphopeptide / iron chelation / liposome / lipid oxidation / muscle phospholipid / volatile compounds / oxygen consumption / TBARS