Highly clean recovery of natural antioxidants from lemon peels: Lactic acid-based automatic solvent extraction

Introduction Food industry generates large amounts of waste by-products rich in natural antioxidants. On the other hand, application of advanced processes for the recovery of these fine chemicals is another popular topic of recent years. Objective The purpose of this study is to propose a green extraction method by application of deep eutectic solvent-based automated solvent extraction (AMSE) from lemon peels. Methods The primary polyphenols (hesperidin, naringin, and p-coumaric acid) and the total polyphenols of the lemon peel extract were quantified and used as response for the optimisation of the AMSE conditions. The Box-Behnken design type of the response surface method (RSM) was chosen for optimisation study. Scavenging activity of the lemon peel extract against 2,2-diphenyl-1-picrylhydrazil (DPPH) free radical was also measured in vitro. Results The optimum conditions for the highest total phenolic (7.47 mg-gallic acid equivalent [GAE]/g-lemon peel [LP]), naringin (5.05 mg/g-LP), p-coumaric acid (3.27 mg/g-LP), and hesperidin (0.07 mg/g-LP) yields were obtained by 1.5 h of extraction time, 46% water (v/v), and 5 g of peel. The antioxidant activity changed between 37.31% and 94.10% in the peels. Conclusions Extraction time was the most effective process factor for the total phenolic and p-coumaric acid yields, while water addition was statistically very important (p < 0.0001) for the naringin and hesperidin yields in the current AMSE system. The second-order models generated for the selected systems represent the data satisfyingly based on the high coefficients of determination (> 0.99), statistically significant p-values (<0.0001), coefficient of variation values (< 10%), and non-significant lack-of-fit values (p > 0.05).

Automated summary

This study proposes a green extraction method using deep eutectic solvent-based automated solvent extraction (AMSE) from lemon peels. The optimal conditions for the highest yields of total phenolic, naringin, p-coumaric acid, and hesperidin were determined, and the scavenging activity of the lemon peel extract against DPPH free radical was measured.