Valorization of the Leucaena leucocephala protein by assessing its functional properties and production of bioactive peptides

Abstract

The Leucaena leucocephala (LL) is a mimosoid legume tree autochthonous from México and Central America. The LL seeds are regionally consumed in traditional dishes due to their high protein content. In this work, LL seeds were used to obtain different materials (whole seed flour, defatted flour, and cotyledon flour) for protein extraction. The obtained LL protein was fractioned and quantified. Higher protein yields were found in cotyledon flour (30.59%), and the most abundant fractions were globulins (83.08%) and glutelins (89.62%). The structure and functional properties (solubility, emulsifying/foaming capacity, and water/oil absorption) of the protein fraction were analyzed. Globulins showed higher structural elements in the FTIR spectrum at amide I and II regions than glutelins. SDS-PAGE analysis showed bands ~50, 37, and 22 kDa in globulins, and in glutelins, a unique clear band (50 kDa) was identified. A higher quantity of essential amino acids in globulins compared to glutelins were found. The functional properties of globulins and glutelins were pH-dependent; both were enhanced by pH values far away from the proteins' isoelectric point. Globulins solubility (72.53%) as well as emulsifying (35.13%), foaming (138.66%), water (3.17 g/g), and oil absorption (1.20 g/g) capacities were significantly higher in comparison to glutelins (62.42 %, 31.69 %, 66.70 %, 2.86 g/g and 0.52 g/g, respectively). Hence, to assess the bioactive properties of LL cotyledon proteins, globulins and glutelins were independently hydrolyzed with; alcalase, trypsin, and α-Chymotrypsin, (E: S 1.0%). Enzyme digestions were carried out up to 180 min. Then, the degree of hydrolysis (DH) and in vitro antioxidant activity (DPPH• and ABTS•+ methods) were measured. The angiotensin I-converting enzyme (ACE-I) inhibitory activity of the hydrolysates was measured by using HHL, as a model peptide, and RP-HPLC, as an analytical method. The a-Amylase inhibition assay was also assessed. The DH differed between the enzymatic systems, and the higher were 76.75% and 82.71% for globulin α-chymotrypsin, and glutelin Alcalase hydrolysates, respectively. The glutelin hydrolysate obtained with trypsin showed the higher DPPH• antioxidant activity while the higher ABTS•+ antioxidant activity was for globulin Alcalase hydrolysate after 180 min of digestion. The highest ACE-I inhibitory activity was 95.44% for globulin Alcalase hydrolysate at 180 min; however, the a-Amylase inhibition assay was 91.51% for glutelinAlcalase at 100 min of reaction. Although LL seed cotyledon protein concentrates and hydrolysates with relatively low mimosine have been prepared stepwise. Such findings indicate that LL resulted in a low-cost and highly available source for protein extraction with desirable functional properties that could be used as an additive for food product development. Bioactive peptides from LL cotyledon proteins could be obtained by enzyme digestion and might be utilized for functional foods with physiological enhancer effects.