Recovery of phenolic compounds from purple onion peel using bio‐based solvents: Thermal degradation kinetics and color stability of anthocyanins

Abstract

The aim of this study was to evaluate the influence of bio-based solvent (ethanol, water, and acetic acid) on the extraction of phenolic (TPC), anthocyanins (TAC), and flavonoids (TFC) from purple onion peel and also analyze the effects of storage temperature on the kinetics of anthocyanin degradation and color stability of the phenolic-rich extract obtained. The purple onion extract obtained with 60% ethanol (E60E) showed, respectively, TPC, TAC, and TFC about 3.4, 2.5, and 4.45 times higher than the other solvents used. E60E showed higher antioxidant and antibacterial potential compared to other solvents. E60E was stored at 4, 25, and 38°C, a half-life of 285, 48.81, and 21.80 days was obtained, respectively. The degradation of anthocyanins in E60E occurred by an endothermic and non-spontaneous reaction with activation energy of 54.65 kJ mol−1, being strongly related to the thermal sensitivity of the phenolic compound. Novelty impact statement Purple onion peel is a food waste rich in bioactive compounds, being a low-cost alternative for obtaining extracts with coloring and functional potential. The results of this study indicate that the purple onion peel is an excellent source for obtaining a phenolic-rich extract with high antioxidant and antimicrobial activity. The anthocyanin, color, and stability index indicates that the extract can applied in several biosectors (e.g., pharmaceutical, cosmetic, and food industries).