Unlocking Quercetin from Apple Pomace through Simultaneous Extraction and Hydrolysis with Glycerol-Based Solvents

Apple pomace is a relevant co-product of juice and cider processing and represents a promising source of phenolic compounds, including glycosylated quercetin. Quercetin is a flavonol widely investigated for its antioxidant and anti-inflammatory potential, making its recovery from agro-industrial co-products attractive for the development of value-added bioactive ingredients. Moreover, the conversion of glycosylated quercetin into its aglycone form may modify its physicochemical and functional properties while enabling the selective recovery of quercetin as a defined target compound (PANDO BEDRIÑANA et al., 2024; PASCOALINO et al., 2025). This study aimed to evaluate COSMO-RS-selected glycerol-based solvents for the simultaneous extraction and acid hydrolysis of quercetin-3-O-β-D-glucoside into quercetin aglycone from apple pomace. Glycerol–citric acid systems were evaluated at glycerol:citric acid ratios of 1:1, 1:2, and 2:1 at 70 °C for 60 min. Hydrochloric acid, selected based on conventional acid hydrolysis procedures reported in the literature (RUPASINGHE; KATHIRVEL; HUBER, 2011), was used as a reference treatment to compare the hydrolytic performance of the glycerol-based systems. The target glycoside and the resulting quercetin aglycone were monitored by ultrahigh-performance liquid chromatography coupled to photodiode array detection (UHPLC-PDA), allowing the extent of hydrolysis and quercetin recovery to be assessed. Among the conditions tested, the glycerol–citric acid system at a 2:1 ratio showed the most promising performance, promoting greater conversion of the glycoside and the highest recovery of quercetin in its aglycone form. These preliminary results indicate that the glycerol–citric acid system may act as a bifunctional medium, combining extraction and acid hydrolysis within a single process. Further experiments are being conducted to characterize the time-dependent conversion of the target glycoside into quercetin and to better understand the relationship between solvent composition, extraction efficiency, and hydrolysis kinetics. Overall, the glycerol–citric acid system showed potential as an alternative medium for the simultaneous extraction and acid hydrolysis of glycosylated quercetin from apple pomace.