Upcycling of Grape Pomace from Malbec, Merlot, Syrah and Grenache: Varietal Effects on Anthocyanin Extract Properties and Performance in Semi-Solid Topical Formulations

Grape pomace represents a widely available agro-industrial by-product in Chile with considerable potential for valorization within circular economy frameworks; however, its functionality as a cosmetic ingredient depends on both grape cultivar and processing strategy. In this study, the direct incorporation of solid grape pomace residues into cream formulations was first evaluated, revealing limitations related to color control, homogeneity, and sensory performance. Subsequently, the influence of varietal origin (Malbec, Merlot, Syrah, and Grenache) on the extraction, stability, color behavior, and functional performance of anthocyanin-rich extracts was investigated for cosmetic applications. pH-standardized color analysis revealed statistically significant (p < 0.05) varietal differences, with Malbec extracts showing superior chromatic stability under acidic and near-neutral conditions, exhibiting lower reduction in a* values across the pH range compared to other varieties. In contrast, Syrah, Grenache, and Merlot showed a more pronounced decrease in red chromaticity, indicating higher sensitivity to pH-induced structural transformations. Although Merlot and Syrah exhibited higher ABTS antioxidant activity, Malbec presented the highest total phenolic content and the most balanced functional profile when considering both stability and color retention. Incorporation of anthocyanin-rich extracts into cosmetic cream formulations demonstrated that a 4.5% (m/v) loading ensured a skin-compatible pH (4.5–5.5), with Malbec-based creams exhibiting superior color stability and formulation performance over time. These findings demonstrate that grape pomace valorization requires variety-specific evaluation and identify extraction as a key enabling step for the development of sustainable, bio-based color-functional cosmetic ingredients.