Optimized green extraction of multifunctional aliphatic and aromatic compounds from suberin-rich agro-industrial potato peel waste

Abstract

Suberin-rich potato peel waste from the food industry was explored as a renewable source of multifunctional aliphatic and aromatic compounds. A green extraction methodology, consisting of an initial water-based extraction followed by alkaline hydrolysis with NaOH, was optimized by varying reaction time (2, 4, 6, and 8 h), temperature (40, 55, 70, 85, and 100 °C), and base concentration (0.1, 0.5, and 1 M). Response surface methodology revealed a strong combined effect of temperature and reaction time, identifying 0.5 M NaOH, 85 °C and 2 h as optimal conditions balancing recovery yield and process sustainability. The composition of the hydrolysates was thoroughly characterized by gas chromatography-mass spectrometry (GC-MS). For comparison, a classic methanolysis protocol using extractive-free potato peels was also applied. In both approaches, the predominant compound families identified were α,ω-dicarboxylic acids and ω-hydroxy fatty acids, with octadec-9-ene-1,18-dioic acid and 18-hydroxyoctadec-9-enoic acid, respectively, as the most abundant components. Additional compound classes included fatty acids, fatty alcohols, monoglycerides, and aromatic derivatives. Unlike the classic method, which results in partial methylation of the carboxylic groups, the green method preserves these functionalities, therefore improving their suitability as potential building blocks for polymer synthesis, as proved by melt-polycondensation for the fabrication of polymer coatings on aluminum substrates. The glycoalkaloids α-solanine and α-chaconine, naturally present in potato peels and highly toxic to humans, were largely removed during processing, as α-solanine was not detected and only trace amounts of α-chaconine could be found in both hydrolysates, likely due to their removal during the extraction steps and precipitation of the remainder under high-pH conditions.