Apple pomace valorisation into antioxidant polyphenols: Multi-criteria process design

Apple pomace is a low-cost source of polyphenolic antioxidants. This study holistically evaluated its valorisation potential by testing extraction techniques, optimising process conditions, selecting operating modes and performing a techno-economic analysis. Conventional solvent extraction (CSE), ultrasound-assisted extraction (UAE) and matrix solid-phase dispersion (MSPD) were compared for polyphenol recovery at lab scale experiments. Chemical characterisation was performed by UV-Vis, measuring total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity and by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantify the individual polyphenols. A Box-Behnken design was used to optimise CSE, yielding 21.95 ± 1.05 mg gallic acid equivalents (GAE)/g dry weight (DW) as TPC under optimum conditions (240 min, 50 °C, liquid-to-solid ratio (LSR) 20 mL/g) using a 50 % ethanol/water solution as solvent at 180 rpm. UAE gave similar results but halved the extraction time. MSPD, using sand as sorbent, required less solvent (LSR 10 mL/g), less time (30 min) and room temperature, but recovered only 66.5 % of the polyphenols (14.61 ± 3.87 mg GAE/g DW) compared to CSE. To evaluate the effect of the operation mode, a laboratory simulation of continuous countercurrent conventional solvent extraction (CCE) was performed at the optimal conditions determined in the CSE. The different processes were modelled in SuperPro Designer and CCE was found to be the most cost-effective configuration, while MSPD was the least economically viable. This study highlights the importance of balancing extraction efficiency, which is often assessed at laboratory scale, with the economic viability of the entire production system. • Valorisation of apple pomace (AP) for nutraceutical production was holistically assessed. • Polyphenol extraction from AP was studied via CSE, UAE, MSPD, and CCE techniques. • UAE & MSPD reduce solvent use and extraction time, but do not improve the extraction. • Continuous countercurrent extraction was the most cost-effective process.