A Natural Approach to Improving Berry Quality in Table Grapes: Inactivated Yeast Extracts

Inactivated yeast extracts derived from S. cerevisiae have recently gained attention as natu-ral and environmentally sustainable elicitors. In this study, the effect of foliar yeast treat-ment on anthocyanin and phenol profiles, antioxidant activity, skin color, and table grape quality characteristics of V. vinifera L. cv ‘Early Cardinal’ and ‘Trakya Ilkeren’ was inves-tigated. Yeast extract (Y) was applied at doses of 0.5 kg ha−1 (Y1), 1 kg ha−1 (Y2), 2 kg ha−1 (Y3), and 4 kg ha−1 (Y4). In Early Cardinal, all yeast doses improved cluster and berry characteristics. In Trakya Ilkeren, cluster weight peaked in the Y3 treatment. No clear trend was observed in sugars and organic acids in either cultivar. Only small variations were observed in total anthocyanins and berry skin color. In Early Cardinal, Y2, Y3, and Y4 treatments significantly increased malvidin-3-O-glucoside, petunidin-3-O-glucoside, and peonidin-3-O-glucoside. In Trakya Ilkeren, the anthocyanin profile remained stable. Total phenol content was measured by the Folin–Ciocalteu assay and expressed as gallic acid equivalents; it increased in all treatments, although no consistent increase in individual phenols was observed. The highest antioxidant activity (DPPH (1,1-diphenyl-2-picrylhydrazyl) and FRAP (ferric reducing antioxidant power)) was detected in Early Cardinal with Y3 and Y4 doses, and in Trakya Ilkeren with Y1 and Y3 treatments. The study provided preliminary insights into improving the quality and nutritional value of table grapes under warm conditions through a natural component of vineyard ecosystems.