Optimization of a Simple Analytical Workflow to Characterize the Phenolic Fraction from Grape Pomace

Abstract

The recovery of polyphenols from grape pomace (GP) supports the promotion of sustainable bioeconomy. Accordingly, the development of pre-treatment and extraction techniques using low-solvent amounts and energy-efficient processes is highly desirable. In this work, a comprehensive strategy to maximize phenol extraction from two Umbrian red wine cultivars, Cabernet Sauvignon and Merlot, was proposed. Focus was paid to sample pre- (fresh, air-, oven- and freeze-dried pomace) and post-extraction (chemical- and enzymatic-hydrolysis) treatments. An experimental design was applied to optimize phenol recovery by ultrasound-assisted extraction: the variables water content in ethanol (20–80% v/v) and time (10–30 min) highlighted a critical influence on the total phenol content (TPC) selected as the response. β-glucuronidase hydrolysis provided the highest TPC and in vitro total antioxidant capacity also improving phenol identification and quantification via HPLC–DAD (particularly evident for freeze-dried Merlot and Cabernet GP, which gave a total phenolic content measured by HPLC equal to 1904.08 mg/g and 2064.64 mg/g, respectively). LC-HRMS/MS analysis allowed identity confirmation of the major phenols, and cytotoxicity assay highlighted the safety of the selected β-glucuronidase extracts towards Caco2 cell line. Ultimately, in the present work, we have addressed the importance of the recovery of bioactive compounds from grape pomace by proposing a comprehensive analytical strategy in which different methodological alternatives have been evaluated to preserve these compounds, in a frame of sustainability on a larger industrial scale.