Fava bean protein isolate (FBPI) was hydrolyzed by Alcalase with different degrees of hydrolysis (DHs), and the role of hydrolysates in oil-in-water (O/W) emulsion stability was investigated. Four emulsions, DH0, DH4, DH9, and DH15, were prepared by 1% (w/v) FBPI hydrolysates with different DHs (0% as the control and 4, 9, and 15%) and 5% (w/v) purified rapeseed oil. The emulsions were monitored for physical and oxidative stability at 37 °C for 7 days. DH4 and DH0 exhibited better physical stability than DH9 and DH15, indicated by droplet size, morphology, and Turbiscan stability index. More importantly, FBPI hydrolysates with DH of 4% most effectively inhibited lipid oxidation (i.e., formation of conjugated dienes and hexanal) while maintaining protein oxidative stability compared to the native and extensively hydrolyzed FBPI. Higher DHs (9 and 15%) induced unduly decreased surface hydrophobicity and increased surface load, which might negatively affect the emulsifying activity. FBPI hydrolysates with DH of 4% had suitable molecular weight for better interfacial layer stability, increased surface net charge for more repulsive electrostatic force, and increased hydrophobicity for better adsorption at the interface and, therefore, may serve as potential natural emulsifiers to maintain both physical and oxidative stability of O/W emulsions.
Keywords: Alcalase hydrolysis; emulsion; fava bean protein; stability.