Non-destructive optical monitoring of grape maturation by proximal sensing.

Naïma Ben Ghozlen,Gwendal Latouche,Zoran G Cerovic,Sandrine Toutain,Claire Germain

doi:10.3390/s101110040

Abstract

A new, commercial, fluorescence-based optical sensor for plant constituent assessment was recently introduced. This sensor, called the Multiplex® (FORCE-A, Orsay, France), was used to monitor grape maturation by specifically monitoring anthocyanin accumulation. We derived the empirical anthocyanin content calibration curves for Champagne red grape cultivars, and we also propose a general model for the influence of the proportion of red berries, skin anthocyanin content and berry size on Multiplex® indices. The Multiplex® was used on both berry samples in the laboratory and on intact clusters in the vineyard. We found that the inverted and log-transformed far-red fluorescence signal called the FERARI index, although sensitive to sample size and distance, is potentially the most widely applicable. The more robust indices, based on chlorophyll fluorescence excitation ratios, showed three ranges of dependence on anthocyanin content. We found that up to 0.16 mg cm−2, equivalent to approximately 0.6 mg g−1, all indices increase with accumulation of skin anthocyanin content. Excitation ratio-based indices decrease with anthocyanin accumulation beyond 0.27 mg cm−2. We showed that the Multiplex® can be advantageously used in vineyards on intact clusters for the non-destructive assessment of anthocyanin content of vine blocks and can now be tested on other fruits and vegetables based on the same model.

Highlights

It is well accepted that premium wine quality depends on the quality of the grapes used to produce it
In addition to the intrinsic linearity of the response of Multiplex® detectors guaranteed by the producer, we have tested the linearity of the ANTH indices themselves using standards of known absorbance
ANTH_RB, corresponding to the ratio of red to blue excitation, is more linear and has less than 10% deviation up to the absorbance of 2

Summary

Introduction

It is well accepted that premium wine quality depends on the quality of the grapes used to produce it. Winemakers commonly have a target ripeness for the fruit according to the wine they want to produce. Pinot Noir intended for champagne sparkling wine production, will have a very different ripeness target compared to that for Pinot Noir still wine. Because the climate during the growth season is one factor beyond the winemaker's control, very different outcomes occur from year to year that influence the decision to harvest [2,3,4]. Even in Champagne, where white wine is primarily produced, there is an increasing trend towards rosé champagne and, an increasing need for quality red wine. Champagne producers have the advantage of being able to mix red and white wines to produce rosé

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