Introduction Enzymatic browning degrades quality safety and

Introduction Enzymatic browning degrades quality, safety, and nutritional values of various fruits or vegetable products. For example, the color of apple or potato is generally yellowish, representing freshness. However, they are extremely susceptible to enzymatic browning because of abundant polyphenol oxidase (Lee et al., 2016, Mosneaguta et al., 2012). Browning of natural products is initiated by enzymatic oxidation of phenols to colored quinones, which are then subjected to further reactions, leading to pigment formation (Nicolas, Richard-Forget, Goupy, Amiot, & Aubert, 1994). Thus, proper control of the browning reaction in natural products has gained attention in the food industry. In the last two decades, there has been great interest in the polyphenol-fortified foods and beverages due to their antioxidant properties (Ganesan and Xu, 2017, Ridgway et al., 1996). The health-promoting effects of polyphenols include anti-aging, anti-cancers, anti-diabetic, anti-inflammatory, anti-bacterial, anti-viral, neuro-protective, and cardio-protective properties (Ganesan & Xu, 2017). In addition, the interest in food additives derived from polyphenol-rich natural products has risen among consumers worldwide because it is believed that they are safer and more reliable than synthetic additives, which are perceived to be associated with adverse effects on health. Therefore, many studies have concentrated on identifying natural food additives to suppress enzymatic browning and improve nutritional values (Espley et al., 2014, Kim et al., 2005, Sudha et al., 2011). Swertiajaponin belongs to the family of flavonoid C-Glycosides. It has been described as a compound found in the whole herb of Swertia japonica (Komatsu, Tomimori, & Makiguchi, 1967). Swertia japonica has been clinically used to treat gastrointestinal disorders including nausea, gastroparesis, and gastric atony in Japan (Kimura & Sumiyoshi, 2011). Furthermore, the Swertia japonica extract with the health benefits caused no gastrointestinal injury such as gastric ulcers, secretion of gastric juice, or change in small intestinal motility in rodents (Yamahara, Konoshima, Sawada, & Fujimura, 1978). Although swertiajaponin, a major compound in Swertia japonica, exhibited biological activities, there is limited research on the function of swertiajaponin as a food additive in the food matrix. Here, we investigated anti-oxidant and anti-browning characteristics of swertiajaponin in potatoes using multiple colorimetric assays and protein-ligand docking simulation.
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Introduction A variety of antioxidant peptides have been isolated from hydrolysates of foods, meat muscles, food byproducts and also from various plant proteins (Agrawal et al., 2016, Chai et al., 2017, Wu et al., 2017, Sudhakar and Nazeer, 2017, Wang et al., 2017, Ramezanzade et al., 2017). The peptide YASGR isolated from a hydrolysate of dark chicken meat showed strong antioxidant activities against peroxyl radical, and the amino Folinic acid synthesis sequence of this peptide matched with the amino acid residues 143–147 of chicken β-actin (Fukada et al., 2016). Functional roles of some antioxidant peptides were demonstrated both in cultured cells and in vivo (Sheih et al., 2010, Himaya et al., 2012, Ko et al., 2013). For example, AREGETVVPG, a peptide isolated from whole wheat products, was suggested to exert a protective role against high glucose-induced oxidative stress in vascular smooth muscle cells (Chen, Lin, Gao, Cao, & Shen, 2017). Additionally, egg white digested with trypsin showed an increasing effect in plasma radical scavenging in spontaneous hypertensive rats (Manso et al., 2008). Various reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated by the metabolism of oxygen in vivo (Villamena, 2013). Super oxide anion, hydrogen peroxide, hydroxyl radical, peroxyl radical, and hypochlorite ion are typical ROS, and peroxynitrite is a representative RNS. The antioxidant activities of the amino acid side chain most likely determines the antioxidant activities of peptides because the thiol in cysteine, thioether in methionine, indole group in tryptophan, phenolic hydroxyl group in tyrosine, and imidazole group in histidine are relatively easily oxidized (Hougland, Darling, & Flynn, 2013). The amino acid sequence also has significant effects on the strength of the antioxidant activity of the peptides (Saito et al., 2003). Ohashi et al. (2015) examined the influence of the type and number of amino acid side chains on the antioxidant activities of tripeptides containing two tyrosines and tripeptides containing two histidines by six different antioxidant activity assays. The unique chemical and physical characteristics related to the amino acid sequence and structure of the peptide are important factors that determine their antioxidant activities (Elias, Kellerby, & Decker, 2008). Although amino acid residues should have different antioxidant activities against different ROS and RNS, the amount of comprehensive research on this subject is limited. One reason why the research is limited is because the conventional methods used to evaluate antioxidants are very time consuming. Our group proposed using a myoglobin method to evaluate the antioxidant activities of peptides against hypochlorite ion, hydroxyl radical, peroxyl radical, and peroxynitrite (Terashima et al., 2007, Terashima et al., 2010). Unlike the ORAC method and the DPPH method, this method uses myoglobin, a biological component, as a probe. The antioxidant property of a substance is evaluated by its ability to suppress the structural change of myoglobin brought about by its reaction with ROS or RNS in this method. Therefore, it can be said that this method more reflects the reactivity of ROS or RNS with biological components than other methods. This protocol was applied to evaluate the antioxidant activities of flavonoids (Terashima et al., 2012), vegetables and beans (Terashima et al., 2013), and Japanese traditional seasoning miso (Morikawa et al., 2014). Since this protocol is simple and quick, it is suitable to analyze many samples in a short time, and successfully applied to screen antioxidant peptides against hypochlorite ion, hydroxyl radical, peroxyl radical, and peroxynitrite (Fukada et al., 2016).