Untargeted Metabolomics Reveals Color-Dependent Nutritional Variation in Raisins: Insights into Composition and Antioxidant Capacity

Raisins come from dried <i>Vitis vinifera</i> L. grapes. They are consumed worldwide, and their shape, color, texture, and taste largely determine consumer preference and market success. Consumers often select raisins based on visual appeal-namely color-without insight into how this relates to nutritional quality. Therefore, this study evaluated raisins of different colors based on non-targeted metabolomics to reveal the nutritional differences among differently colored raisins and to measure the differences in antioxidant capacity. Compared with green raisins ('Sultanina'), 377-381 differential metabolites were identified in other colored varieties. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that these metabolites were enriched in pathways such as 'biosynthesis of other secondary metabolites' and 'amino acid metabolism'. The comparison of the antioxidant capacity of raisins of different colors shows that the darker the color of the raisins, the stronger their antioxidant capacity. Correlation analysis between total antioxidant capacity and 14 differential metabolites showed a significant positive correlation. Notably, syringetin levels in black raisins ('Blackcurrant' and 'Sweet Sapphire') were substantially higher-148.31 and 515.94 times greater, respectively-than in green raisins ('Sultanina'). This elevated syringetin content may significantly contribute to the enhanced antioxidant capacity of black raisins. Furthermore, based on the positive ion mode, the relative contents of 24 and 12 differential metabolites were relatively high in green and red raisins, respectively. The negative ion model identified that 19 and 4 differential metabolites had relatively high contents in green and red raisins. These metabolites may be linked to the unique health benefits of red and green raisins. This study provides valuable insights for consumers selecting raisins based on health needs and for companies developing raisin-based health products.