J Food Biochem. 2020;00:e13396. wileyonlinelibrary.com/journal/jfbc | 1 of 13 https://doi.org/10.1111/jfc.13396 © 2020 Wiley Periodicals LLC. 1 | INTRODUCTION Food proteins have gained increasing value in recent times because of the rapidly expanding research and knowledge based on the contents of encrypted physiologically active amino acid sequences (Miguel, Alonso, Salaices, Aleixandre, & López-Fandiño, 2011). Proteins from food sources usually contain specific peptide sequences that remain inactive when present as intrinsic parts of the primary protein struc- ture and one of the most reliable ways to release these peptides is through enzymatic hydrolysis of parent protein (Aluko, 2015). Received: 1 March 2020 | Revised: 1 July 2020 | Accepted: 6 July 2020 DOI: 10.1111/jfbc.13396 SPECIAL ISSUE ORIGINAL ARTICLE Antioxidant and enzymes inhibitory properties of Amaranth leaf protein hydrolyzates and ultrafiltration peptide fractions Akinsola A. Famuwagun 1,2 | Adeola M. Alashi 1 | Olasunkanmi S. Gbadamosi 2 | Kehinde A. Taiwo 2 | Durodoluwa Oyedele 3 | Odunayo C. Adebooye 4 | Rotimi E. Aluko 1 1 Department of Food and Human Nutritional Sciences, University of Manitoba, Winnipeg, MB, Canada 2 Department of Food Science & Technology, Obafemi Awolowo University, Ile-Ife, Nigeria 3 Department of Soil and Land Resources Management, Faculty of Agriculture, Obafemi Awolowo University, Ile-Ife, Nigeria 4 Department of Agronomy, Faculty of Agriculture, Obafemi Awolowo University, Ile-Ife, Nigeria Correspondence Akinsola A. Famuwagun, Department of Food and Human Nutritional Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada. Email: akinsolaalbert@gmail.com Funding information International Development Research Centre and Global Affairs Canada through the Canadian International Food Security Research Fund, Grant/Award Number: 107983 Abstract Amaranth leaf protein isolate (ALI) was hydrolyzed using four different proteases (al- calase, trypsin, pepsin, and chymotrypsin) followed by fractionation of the pepsin hydrolyzate (PH) into different sizes using ultrafiltration membrane. Gel permeation chromatography showed that all the hydrolyzates had smaller size peptides ( <7 kDa) than the protein isolate (>32 kDa). The chymotrypsin hydrolyzate had higher contents of hydrophobic amino acid (44.95%) compared to alcalase (42.72%), pepsin (43.93%), and trypsin (40.95%) hydrolyzates. The PH had stronger DPPH, hydroxyl radical, and superoxide radical scavenging activities than the other protein hydrolyzates but weaker Ferric reducing antioxidant power and metal chelating activities when compared to the peptide fractions. The <1 kDa peptide fraction exhibited stronger DPPH, hydroxyl, and superoxide radicals scavenging activities than the higher mo- lecular weight (> 1 kDa) fractions. Fractionation of PH also resulted in enhanced inhi- bition of α-amylase and ACE activities but weaker α-glucosidase inhibition. Practical applications ALI was hydrolyzed using four proteases to produce protein hydrolyzates. The most active of the hydrolyzate was then fractionated to produce fractions of different mo- lecular sizes. The results of the analyses showed that the hydrolyzates and the frac- tions showed good antioxidant and enzyme inhibitory activities such as the inhibition of ACE, α-amylase, and glucosidase enzymes. The results suggest that the enzymatic hydrolyzates and peptide fractions could be used as ingredients in the nutraceuti- cal and functional food industries to scavenge free radicals and inhibit angiotensin- converting enzyme activity. KEYWORDS ACE inhibition, antioxidant properties, leaf protein hydrolyzate, α-amylase, α-glucosidase