Enhancement of Bioactive Compounds in “Valencia” Orange Peel Waste During Cold Storage by Melatonin and Arginine Treatments

This study was carried out to investigate the protective effects of melatonin (Mel) and arginine (Arg) treatments on the maintenance and enhancement of bioactive compounds in Valencia orange peel, including soluble sugars, organic acids, and phenolic compounds, during 6 months of cold storage. This research was conducted to optimize storage conditions and increase the added value of orange peel as a rich source of functional compounds in the food and pharmaceutical industries. The 1 mM-Mel treatment increased fructose by 14%. Glucose content decreased in the control, 2 mM-Mel, 5 mM-Arg, and 10 mM-Arg treatments, but remained constant at 1 mM-Mel. Sucrose content increased by 46% at 10 mM-Arg. Ascorbic acid increased by 145% with 1 mM-Mel and by 90% with 10 mM-Arg. Citric acid increased by 173% with 1 mM-Mel and by 102% with 1 mM-Arg. Coumaric acid increased by 44% with 1 mM-Mel and remained constant at 10 mM-Arg. <i>Trans</i>-ferulic acid increased by 50% with 5 mM-Arg. Chlorogenic acid increased by 103% with 1 mM-Mel. Catechin increased by 15% with 10 mM-Arg. Quercetin increased by 292% with 10 mM-Arg. Hesperidin increased by 35% with 10 mM-Arg and hesperetin by 74% with 10 mM-Arg. Mel and Arg maintained the bioactive compounds of orange peel during cold storage. They are potential treatments to increase the added value of agricultural products by preserving bioactive compounds.