Bridging the Gap: The challenge of Standardizing Antioxidant Assessment for Highly Active Grape Pomace Extracts
Maria Lucia Ciorba*, Cãlina Cristina Ciont, Floricuța Ranga, Oana Lelia Pop, Simona Codruța Hegheş, Dan Cristian Vodnar, Oana-Alina Hoteiuc and Ramona Suharoschi
ABSTRACT
Oxidative stress, a foundational imbalance linked to chronic inflammation, is implicated in numerous debilitating diseases, spurring interest in functional foods rich in natural antioxidants. Grape pomace (GP), an abundant agricultural by-product, is exceptionally rich in polyphenols and exhibits antioxidant properties superior to other berry wastes, making it a powerful long-term nutritional solution. This review provides a critical analysis of methodologies used to quantify GP's antioxidant activity (AO): spectrophotometric, electrochemical, chromatographic, nanosensors, and biosensors. While newer sensor technologies offer high sensitivity and a theoretically better correlation with in vivo systems, most traditional chemical assays suffer from poor reproducibility and a lack of correlation between in vitro results and biological outcomes. The core challenge lies in the chemical diversity of antioxidants, where no single test can fully assess the capacity to neutralize all relevant radicals. Consequently, accurately measuring the antioxidant potential of GP currently requires a multi-system approach, such as calculating the Relative Antioxidant Capacity Index (RACI), integrating comprehensive chromatographic profiling with detection methods or using Caenorhabditis elegans and rats as in vivo models. However, the absence of a universal, standardized working protocol—both for extraction and analytical measurement—significantly hinders reproducibility across laboratories and makes definitive statements about the antioxidant power of grape pomace polyphenols difficult. Addressing this lack of standardization is the crucial next step for validating GP as a bioactive ingredient. The novelty of this article consist of the critical synthesis of why diverse methods (from spectrophotometry to nanosensors and in vivo AO assays) fail individually and why RACI or similar multi-metric approaches are necessary, connecting this failure back to the chemical complexity of GP
