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

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.