Extraction optimization for polyphenolic profiling and bioactive enrichment of extractives of non-pomace residue from grape processing

A simple and fast extraction method combining mechanical orbital agitation (MOA) and hydroalcoholic solid-liquid extraction (HSLE) was optimized for polyphenol enrichment and bioactive profiling of extractives of the non-pomace residue obtained from grape industries. Using this potentially reusable material, solid-liquid extractions using a mixture of organic-water solvents and rotational agitation were evaluated in order to obtain antioxidant rich extractives of this highly-colored residue, which is industrially discarded as a solid waste. In addition, the phenolic profile of this residue was firstly identified by RP-LC DAD. The extraction of many phenolic compounds was greatly increased by increasing solvent polarity combined with plate or orbital agitation. The non-pomace extractives showed high levels of flavanols, phenolic acids, anthocyanins and stilbene, whereas polyphenolic concentrations were significantly higher in methanolic extracts. The complete three-level factorial design allowed the optimization of extraction time, solvent concentration, and solid-liquid ratio, leading to an optimal extraction of anthocyanins at a solvent:solid ratio of 1:10 (w/v), extraction time of 5 min and solvent concentration of 85%. Malvidin glucosides were the major phenolics in the non-pomace residue. Catechin, epicatechin, ferulic acid, caffeic acid and trans-resveratrol, which are potent antioxidants, were found at high concentrations in the extractives, suggesting a bioactive interest for further technological applications.