Microwave-assisted extraction of polysaccharides from fruit pomace using natural deep eutectic solvent system

Abstract

Advancing circular bioeconomy goals, this study addresses the combined dilemma of food waste and resource scarcity by converting raspberry pomace, a pectin-rich but underutilized processing residue, into functional biopolymers through sustainable extraction. This research compares the sustainability and efficiency of microwave-assisted extraction (MAE) with traditional hot water extraction (HWE) in combination with natural deep eutectic solvents (NADES) to recover pectin from Raspberry Pomace. Six solvents were tested, including reagent A, 10% reagent B, 10% reagent C, a non-eutectic mix of reagent C: reagent B in molar ratio X, and two NADES (reagent C: reagent B at X and Y molar ratios). MAE greatly increased extraction efficiency, saving extraction-phase energy consumption by 17% and processing time by 87.5% (shortened compared to extended extraction time for HWE). The highest pectin yield was obtained with Mix (X) under MAE (9.52%), whereas NADES (X) performed best in HWE (6.39%). Dialysis successfully eliminated low-molecular weight impurities though significant yield losses of up to 54.9% were observed. The compositional analysis showed that MAE was better at maintaining polymeric pectin, with NADES (X) extracts 34.75% saccharides and 58.90% uronic acid (UA). Structural characterization by GC-MS and ATR-FTIR showed that acidic NADES (Y) produced linear homogalacturonan (HG)-rich pectin (78.12% GalA; Rha/GalA = 0.05), whereas reagent A extracts contained branching rhamnogalacturonan-I (RG-I) (29.26% GalA; Rha/GalA = 0.22). UA purity (65.89%) and linearity for gelling applications were maximized by NADES-HWE, but MAE with Mix (X) favoured higher yields/saccharides (36.03%) appropriate for emulsification. This work introduces NADES-MAE as a sustainable platform for biomass valorization by offering variable pectin functionality via solvent-driven structural control.