Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Research Article Peptidomic analysis of hydrolyzed oat bran proteins, and their in vitro antioxidant and metal chelating properties Ramak Esfandi a , William G. Willmore a,b,c , Apollinaire Tsopmo a,c, ⁎ a Food Science and Nutrition Program, Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada b Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada c Institute of Biochemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada ARTICLE INFO Keywords: Oat peptide Antioxidant Oxidative stress Metal chelation Radical scavenging ABSTRACT Peptide profiles of hydrolyzed oat proteins and the susceptibility of their polypeptides to proteolytic cleavages were determined using peptidomic analysis. In addition, antioxidant activities were also measured. Proteins isolates were first extracted with carbohydrases, Viscozyme or Cellulase and then hydrolyzed with proteases (Alcalase, Papain, Protamex, Flavourzyme). Amongst the eight hydrolysates, Viscozyme-proteins hydrolyzed with Papain showed the highest ability to quench ABTS %+ radicals (866.9 ± 10.6 μM TE/g) and to chelate ferrous ions (75 ± 0.4%) while displaying the second strongest activity for ROO % radicals (396.7 ± 14.0 μM TE/g). Peptidomics analysis showed that the higher activity of papain hydrolysate in most assays was related to its greater proteolytic action on main proteins (avenin, 11S- and 12S-globulins) compared to other proteases. In addition, the number of peptides identified in the Papain digest of proteins extracted with Viscozyme was about half relative to the number in proteins from bran treated with Cellulase and digested with the same protease. This was likely because the carbohydrases differently affected polypeptide secondary structures. 1. Introduction The oxidation of molecules in foods is a major cause of quality de- terioration and results in the formation of undesirable off-flavours and unhealthful compounds. The oxidation can, as well decrease the con- tent of essential nutrients, produce dimers or polymers of lipids and proteins (Choe & Min, 2009). Various conditions can cause oxidative deterioration of foods including storage, availability of oxygen, irra- diation, exposure to light or thermal treatments (Choe & Min, 2009). Enzymes such as lipoxygenases and transition metals are also re- sponsible for the oxidation of lipids. Initial oxidation products are often radical species that easily form chain reactions or polymerize and hence, the need of compounds (i.e. antioxidants) that can stop the re- action. Antioxidants work by slowing down the oxidation rates of food compounds by a combination of free radical scavenging, chelation of pro-oxidant transition metals, quenching of singlet oxygen and photo- sensitizers, or inactivation of lipoxygenase (Baakdah & Tsopmo, 2016; Ratnasari, Walters, & Tsopmo, 2017). Extensive work has been done to extract, purify, and identify various antioxidant molecules most of which are polyphenols and carotenoids (Anunciato & da Rocha Filho, 2012). Oats contain essential nutrients and phytochemicals many of which possess relatively good health benefits in comparison to other grain cereals. Their starch content ranged from 27.3 to 50.0%, fibres 13.6 to 30.2%, proteins 9.7 to 17.3% and unsaturated fatty acids 5.2 to 12.4% (Sterna, Zute, & Brunava, 2016). Oats have the highest amount of proteins amongst cereals and they are composed of globulins (50–80%), albumins (1–12%), prolamins (4–15%) and glutenins (< 10%) (Klose & Arendt, 2012). Proteins from oats and other foods are beneficial, meanwhile, many applications have digested them with proteases to release peptides that will enhance their biological functions. Proteins from oat and other foods have nutritional value and functional prop- erties (e.g. emulsification, foaming) (Walters, Udenigwe, & Tsopmo, 2018), however, literature data on their use as sources of biologically active peptides have been accumulating (Carrasco-Castilla et al., 2012; Kamdem & Tsopmo, 2017). These proteins are first extracted from foods with salts or alkaline conditions followed by their recovery by cen- trifugation at isoelectric points. In many cases, the treatment of the food material with polysaccharide degrading enzymes did enhance proteins extraction yields (Bauer, Vasu, Persson, Mort, & Somerville, 2006; Jodayree, Smith, & Tsopmo, 2012). To produce bioactive peptides, protein concentrates, or isolates are treated with proteases followed by https://doi.org/10.1016/j.foodchem.2018.11.110 Received 2 August 2018; Received in revised form 12 November 2018; Accepted 25 November 2018 ⁎ Corresponding author at: Apollinaire Tsopmo, Food Science and Nutrition Program, Department of Chemistry, Carleton University, 1125 Colonel By Drive, K1S 5B6 Ottawa, ON, Canada. E-mail address: apollinaire_tsopmo@carleton.ca (A. Tsopmo). Food Chemistry 279 (2019) 49–57 Available online 06 December 2018 0308-8146/ © 2018 Elsevier Ltd. All rights reserved. T