Membrane fractionation improved the multifunctional properties of fava bean protein hydrolysate

• Essential and hydrophobic amino acids were highest in the <1 kDa peptide fraction. • Membrane fractionation improved the DPPH and superoxide radical scavenging activities. • Inhibitions of α-amylase and pancreatic lipase were inversely related to peptide size. • The <1 kDa peptide fraction had the strongest inhibition of angiotensin converting enzyme. In this study, the effects of membrane ultrafiltration and peptide size on the amino acid profile and in vitro bioactive properties of fava bean pepsin protein hydrolysate (FBPH) were determined. FBPH was fractionated sequentially using regenerated cellulose membranes with molecular weight cut-offs of <1 kDa, 1–3 kDa, 3–5 kDa, 5–10 kDa, and >10 kDa to elucidate structure-function relationships among peptide fractions. Results obtained showed that membrane fractionation markedly enhanced amino acid profile with the <1 kDa exhibiting significantly ( p < 0.05) higher contents of essential amino acids (47.38 %), branched chain amino acids (23.87 %), hydrophobic amino acids (50.68 %), aromatic amino acids (13.65 %), and arginine to lysine ratio (1.65) in comparison to other peptide fractions (35.68–43.60 %; 13.37–21.16 %; 31.18–45.91; 6.99–11.04 %; and 1.44–1.49, respectively) and the unfractionated hydrolysate - FBPH (39.49 %; 17.44 %; 38.71 %; 9.22 % and 1.46, respectively). Also, membrane fractionation improved the DPPH and superoxide radical scavenging activities as well as inhibition of linoleic acid peroxidation of the peptide fractions when compared to the FBPH. The α-amylase, pancreatic lipase and acetylcholinesterase inhibitory activities of the membrane fractions demonstrated increases that corresponded with decreases in the molecular weight of the peptide fractions. However, the <1 kDa fraction had the strongest ( p < 0.05) inhibition of angiotensin converting enzyme while FBPH inhibited arginase activity the most. In conclusion, membrane ultrafiltration of pepsin-hydrolyzed fava bean protein generated active peptides with the <1 kDa sizes being the most active. Therefore, pepsin-hydrolyzed fava bean protein and its membrane fractions could be useful ingredients to formulate functional foods against oxidative stress and associated degenerative diseases.