Assessment of "Sugranineteen" Table Grape Maturation Using Destructive and Auto-Fluorescence Methods

The optimal harvesting of table grapes is commonly determined based on technological and phenolic indices analyzed over the course of its maturity. The classical techniques used for these analyses are destructive, time-consuming, and work for a limited number of samples that may not represent the heterogeneity of the vineyard. This study aimed to follow the ripening season of table grapes using non-destructive tools as a rapid and accurate alternative for destructive techniques. Grape samples were collected from a Sugranineteen vineyard during the ripening season to measure the basic maturity indices via wet chemistry, and total polyphenols, anthocyanins, and flavonoids were evaluated by spectrophotometry. Fluorescent readings were collected from intact clusters with a portable optical sensor (Multiplex^® 3, Force-A, France) that generates indices correlated to different maturity parameters. Results revealed strong relationships between the Multiplex^® indices ANTH_RG and FERARI and the skin anthocyanin content, with R² values equal to 0.9613 and 0.8713, respectively. The NBI_R index was also related to total anthocyanins (R² = 0.8032), while the SFR_R index was linked to the titratable acidity (R² = 0.6186), the sugar content (R² = 0.7954), and to the color index of red grapes (CIRG) (R² = 0.7835). Results demonstrated that Multiplex^® 3 can be applied on intact clusters as an effective non-destructive tool for a rapid estimation of table grapes' anthocyanin content.