Extraction and fractionation of phenolic acids and glycoalkaloids from potato peels using acidified water/ethanol-based solvents

• Phenolic acids and glycoalkaloids were extracted from potato peels.
• Methanolic and ethanolic (food grade) extracts were comparable.
• Glycoalkaloids and phenolic acids were successfully separated by solid phase extraction.
• Caffeic acid was recovered by alkaline hydrolysis and solid phase fractionation.

Potato processing generates potato peels as byproducts. Methanolic extracts from the peels result in mixtures of phenolic acids and glycoalkaloids. Phenolic acids have potential for food applications owing to their antioxidant and antibacterial properties. However, when extracted from potatoes, their separation from toxic glycoalkaloids is needed prior to their applications in foods. Moreover, glycoalkaloids may be used as feedstock for synthesis of pharmaceuticals. This study aimed to develop a method for the extraction and fractionation of phenolic acids and glycoalkaloids from potato peels using food grade water/ethanol-based solvents. Samples were analyzed by ultrafast liquid chromatography (UFLC) and/or ultrafast liquid chromatography–mass spectrometry (UFLC–MS). A methanol-based solvent for extraction was used as a control to be compared with two aqueous ethanolic solvents acidified with acetic acid. The recovery of the predominant compounds from potato peels was comparable for all three solvents. Extraction yielded per 100 g of potato peel fresh weight 17.0 mg α-chaconine, 7.1 mg α-solanine, 0.1 mg solanidine, 4.8 mg caffeic acid, 13.3 mg neochlorogenic acid, and 77.6 mg chlorogenic acid. More than 90% of these compounds were recovered after two consecutive extractions. The crude extract was fractionated by solid-phase extraction at pH 7 and eluted with aqueous ethanol. Quantitative recovery of the phenolic acids and glycoalkaloids was achieved in their corresponding fractions. Hydrolysis followed by solid-phase fractionation of the crude extract allowed recovery of 139 μmol caffeic acid/100 g potato peel fresh weight. Partial degradation of caffeic acid and glycoalkaloids occurred during the process. Degradation of caffeic acid can be likely mitigated by the addition of antioxidants and metal chelators. The method developed in this study allows the sustainable recovery of secondary plant metabolites from potato peels and their fractionation using food grade water/ethanolic solvents for application of phenolic extracts free of toxic glycoalkaloids for food preservation, and of glycoalkaloid extracts for synthesis of pharmaceuticals.