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

Najwane Hamie,Luigi Tarricone,Giuseppe Gambacorta,Michele Faccia,Vincenzo Verrastro,Giuseppe Natrella

doi:10.3390/foods11050663

Abstract

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.

Highlights

Publisher’s Note: MDPI stays neutralThe maturity assessment of table grapes (Vitis vinifera L.) is necessary to determine the optimal harvesting time, which is a critical point for the postharvest handling period
Among the parameters that Multiplex® 3 (MP3) can measure, this study focuses on the measurement of skin anthocyanins using 2 indices: ANTH_RG, which is based on the chlorophyll fluorescence excited with red (R) and green (G) lights, and FERARI, which is based on the far-red chlorophyll fluorescence under red excitation [12,17]
The sugar content had an increasing trend, while the acidity was decreasing during maturation and reached at harvest an average TSS of 17.9 ◦ Brix and an acidity value of 4.86 g/L with no significant differences among the blocks

Summary

Introduction

The maturity assessment of table grapes (Vitis vinifera L.) is necessary to determine the optimal harvesting time, which is a critical point for the postharvest handling period. Both destructive and non-destructive methods are applied in viticulture for crop monitoring and evaluation [1]. A common practice is to harvest the grapes based on technological and phenolic maturity indices that are measured using destructive laboratory analyses [2]. The technological maturity mainly includes the measurement of sugar content, titratable acidity, and the pH value of grape juice. The total phenolic compounds are usually extracted from grape skins and estimated via spectrophotometry methods, such as the

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