Peptide profiling and antioxidant capacity of white grape juice using LC-MS approach

Abstract

The oxidative stability of white wine is governed by a complex network of native metabolites collectively described as the wine antioxidant metabolome1. Beyond polyphenols and glutathione, this metabolome includes diverse nitrogen- and sulfur-containing compounds that buffer oxidation reactions and influence white wine ageing. Peptides have recently emerged as a potentially important, yet largely unexplored, fraction of this antioxidant metabolome. Their expected variability with vintage, grape variety and pre-fermentation practices, particularly for thiol-containing (thiolated) peptides, highlights the need for dedicated analytical workflows to investigate the peptidic composition of grapes and its link to wine oxidative stability. We hypothesize that part of the peptide pool is established during grape ripening and extracted into must during pressing. Because grape proteins occur at low levels in must and are progressively degraded during winemaking, peptide characterization requires enrichment of protein precursors followed by controlled peptide generation. After building the workflow to get a pool of peptides extracted from the must (protein concentration via dedicated purification steps, enzymatic digestion, and qualitative controls of recovery/digestion efficiency), we now focus on comprehensive peptide profiling using LC-QTOF-MS metabolomics. To expand chemical coverage, we compared two complementary chromatographic modes: reverse-phase HSS T3 (favoring less polar features) and HILIC (optimized for polar compounds). After digestion, extracts were evaporated and reconstituted in an acidic buffer (pH 3.0) at 2-10 mg mL-1, then injected in triplicate to ensure reproducible feature detection. This approach allows evaluation of peptide separation efficiency across both columns and assessment of shared versus complementary peptide-related mass features between systems. In parallel, the antioxidant capacity of peptide-rich fractions was screened using a DPPH assay to evaluate radical-scavenging activity. Overall, this work validates an analytical pipeline to profile grape/must-derived peptides and explore their antioxidant potential, opening new perspectives for managing white-wine oxidative stability from the vineyard and early winemaking stages.

References

1. Romanet, Rémy, Zina Sarhane, Florian Bahut, et al. (2021). Exploring the chemical space of white wine antioxidant capacity: A combined DPPH, EPR and FT-ICR-MS study. Food Chem, 335.