Extraction of Antioxidants from Grape and Apple Pomace: Solvent Selection and Process Kinetics

Featured Application Several promising aqueous mixtures are selected for the fast extraction of functional antioxidant mixtures from apple and grape pomaces. Polyphenols have become a research target due to their antioxidant, anti-inflammatory and antimicrobial activity. Obtention via extraction from natural sources includes the revalorization of food wastes such as grape pomace (GP) or apple pomace (AP). In this work, GP and AP were submitted to a liquid-solid extraction using different solvents of industrial interest. Process kinetics were studied measuring the total phenolic content (TPC) and antioxidant capacity (AC), while the extraction liquor composition was analyzed employing chromatographic methods. Extraction processes using water-solvent mixtures stood out as the better options, with a particular preference for water 30%-ethanol 70% (v/v) at 90 degrees C, a mixture that quickly extracts up to 68.46 mg GAE/gds (Gallic Acid Equivalent per gram dry solid) and 122.67 TEAC/gds (TROLOX equivalent antioxidant capacity per gram dry solid) in case of GP, while ethylene water 10%-ethylene glycol 90% (v/v) at 70 degrees C allows to reach 27.19 mg GAE/gds and 27.45 TEAC/gds, in the case of AP. These extraction processes can be well-described by a second-order kinetic model that includes a solubility-related parameter for the first and fast-washing and two parameters for the slow mass transfer controlled second extraction phase. AP liquors were found to be rich in quercetin with different sugar moieties and GP extracts highlighted flavonols, cinnamic acids, and anthocyanins. Therefore, using identical extraction conditions for AP and GP and a comparative kinetic analysis of TPC and AC results for the first time, we concluded that ethanol/water mixtures are adequate solvents for polyphenols extraction due to their high efficiency and environmentally benign nature.

Automated summary

This study selected several promising aqueous mixtures for the fast extraction of functional antioxidant mixtures from apple and grape pomaces. It was found that water-solvent mixtures, particularly 30% water-70% ethanol (v/v) for grape pomace (GP) and 10% ethylene water-90% ethylene glycol (v/v) for apple pomace (AP), were the better options for extraction. The extraction processes could be well-described by a second-order kinetic model.