Valorization of minority red grape residues for sustainable gold nanoparticle synthesis: A matrix-dependent approach

Abstract

This research investigates the potential of four minority red grape varieties from Northwest Spain—Bruñal, Cenicienta, Mouraz, and Puesto Mayor—as sustainable bio-templates for the green synthesis of gold nanoparticles (AuNPs). In the framework of a circular bioeconomy, the study evaluates how the specific chemical “fingerprint” of different winery residues (musts, skins, and seeds) regulates the final properties of the nanomaterials. The results establish a clear functional specialization based on the tissue-specific phytochemical profile. Skin extracts, characterized by high anthocyanin concentrations (up to 388 mg/L in Cenicienta), acted as superior stabilizing media, yielding the smallest nanoparticles. Specifically, Puesto Mayor skin extracts produced ultra-small primary nuclei of 3.16 nm. In contrast, seed extracts, rich in condensed tannins (TPI ~28), served as powerful reducing engines. However, the massive production of nuclei in seeds often leads to vertical stacking phenomena upon dehydration, as evidenced by Atomic Force Microscopy (AFM). Analysis of must-derived AuNPs revealed inhomogeneous matrices where gold nuclei are embedded in voluminous organic “rafts” of sugars and polysaccharides, explaining the large hydrodynamic diameters (>400 nm) detected by DLS. Morphological characterization via AFM provided definitive validation of this matrix-dependent growth. While seed-derived AuNPs were predominantly spherical, skin extracts from Cenicienta and Mouraz promoted the formation of triangular nanoprisms. This anisotropic growth is attributed to the high total acidity and specific phenolic hydroxyl groups acting as shape-directing agents. The high colloidal stability achieved, with Zeta potential values reaching –39.00 mV in Mouraz seeds, highlights the efficiency of grape-derived phenolics as robust surface protectors. Ultimately, this work valorizes the unique chemical profiles of underutilized viticultural biodiversity, demonstrating that winery by-products can be transformed into high-added-value technological resources for strategic applications in food science and biomedicine.

References

Sujitha, M. V.; Kannan, S. (2013). Green synthesis of gold nanoparticles using Citrus fruits extracts and its catalytic activity. Spectrochim. Acta A Mol. Biomol. Spectrosc., 102, 15-23.