# Functional Characterization of Mung Bean Meal Protein-Derived Antioxidant Peptides
###### Abstract  
The aim of this work was to characterize the antioxidant properties of some of the peptides present in bromelin mung bean meal protein hydrolysate (MMPH). The MMPH was subjected to two rounds of bioassay-guided reversed-phase HPLC separation followed by peptide identification in the most potent fractions using tandem mass spectrometry. Twelve antioxidant peptides, namely, HC, CGN, LAN, CTN, LAF, CSGD, MMGW, QFAAD, ERF, EYW, FLQL, and QFAW were identified and assayed for antioxidant properties. CTN, HC, CGN, and CSGD were the most potent (\(p<0.05\)) DPPH radical scavengers with EC\({}_{50}\) values of 0.30, 0.29, 0.28, and 0.30 mg/mL, respectively, which are lower than the 0.03 mg/mL obtained for reduced glutathione (GSH). CTN, HC, CGN, and CSGD exhibited the most potent (\(p<0.05\)) scavenging activities against hydroxyl and superoxide radicals with EC\({}_{50}\) values that are similar to those of GSH. The cysteine-containing peptides also had stronger ferric reducing antioxidant power and metal chelation activity than peptides devoid of cysteine. In contrast, MMGW, ERF, and EYW had poor radical scavenging and metal chelation activities. We conclude that the availability of the sulfhydryl group may have enhanced antioxidant potency while the presence of bulky groups such phenylalanine and tryptophan had an opposite effect.  
mung bean; bromelin; membrane ultrafiltration; protein hydrolysate; antioxidant; peptide sequencing; RP-HPLC +
Footnote †: journal: Medical  
compounds are being studied as potential replacements for synthetic antioxidants. In order to be acceptable alternatives, these compounds should be able to neutralize ROS and prevent or reduce cellular damages. One of the most studied natural alternatives to synthetic antioxidants are the food protein-derived peptides, which are normally obtained through enzymatic hydrolysis of food proteins and have been extensively evaluated for potential therapeutic functions in preventing cellular damages from oxidative stress and promoting human health [7]. Bioactive peptides normally contain 2-20 amino acid residues with low molecular weight and have a variety of biological activities depending on the type of amino acid, molecular size, and sequence [8; 9]. The antioxidant activities of several plant protein-derived peptides have been determined including chickpea [10; 11], wheat [12], barley [13], soybean [14], corn [15], rapeseed [16; 17], and mung bean [18; 19; 20; 21].  
Mung bean meal is a by-product from vermicelli processing and is usually discarded as waste even though it has approximately 70% protein (\(w/w\) dry basis). In a previous study, mung bean meal was produced as a flavor enhancer using enzymatic hydrolysis with bromelain [22]. Peptides and free amino acid in the hydrolysate are key compounds for its flavor and taste. However, these peptide and amino acids could play various functional properties and bioactive activities, including the ability to act as antioxidants. Previous studies have reported other bioactive properties in mung bean peptides and protein hydrolyses such as antihypertensive [23; 24], anti-allergic [25], and anti-tumor [26]. However, only few studies have reported the antioxidant activities of specific peptide sequences derived from mung bean protein hydrolysate. Moreover, research exploring the active sequences of the antioxidant peptides obtained from mung bean protein hydrolysate using bromelain is limited. Knowledge of amino acid sequence is critical to elucidating structure-function properties with a view to developing highly potent antioxidant peptides. Therefore, this study was carried out to identify and determine the in vitro functional performance of antioxidant peptide sequences present in a bromelain mung bean protein hydrolysate.