Assessment of Maturity of Loire Valley Wine Grapes by Mid-Infrared Spectroscopy
Total Page:16
File Type:pdf, Size:1020Kb
picque 24/12/10 14:15 Page 219 ASSESSMENT OF MATURITY OF LOIRE VALLEY WINE GRAPES BY MID-INFRARED SPECTROSCOPY D. PICQUE1*, Pascale LIEBEN1, Ph. CHRÉTIEN2, J. BÉGUIN3 and L. GUÉRIN3 1: Unité Mixte de Recherche 782 Génie et Microbiologie des Procédés Alimentaires (AgroParisTech-INRA), BP 1, 78850 Thiverval-Grignon, France 2: Institut Français de la Vigne et du Vin (IFV, Anjou Unit), 42 rue Georges Morel, BP 60057 49070 Beaucouzé cedex, France 3: Institut Français de la Vigne et du Vin (IFV, Touraine Unit), 46 Avenue Gustave Eiffel, BP 39537, 37095 Tours cedex 2, France Abstract Résumé Aim: The objective of the present study was to assess the ripening of grapes Objectifs : L’objectif de ce travail est d’évaluer la maturation de baies collected at different stages of maturation between the “véraison” and de raisin collectées entre la véraison et la récolte par spectroscopie moyen harvest periods from mid-infrared spectroscopy (MIRS) analysis. infra rouge (MIRS). Methods and results: Grape berries of Cabernet Franc collected in two Méthodes et résultats : Les baies de raisin ont été collectées dans deux locations of the Loire Valley region (Touraine and Anjou), from 28 vine régions de la vallée de la Loire (Touraine et Anjou) sur 28 parcelles au plots and during two vintages (2005 and 2006) were analysed. With principal cours de deux millésimes (2005 et 2006). À partir d’une analyse en component analysis (PCA) of spectral data of grape musts, different levels composantes principales (ACP) des spectres MIR des moûts issus des of ripening were described during the three to four weeks before harvest. baies de raisin, différents niveaux de maturation sont mis en évidence A separation according to origin (Touraine or Anjou) was also observed durant les trois à quatre semaines précédant la récolte. Une séparation selon and confirmed by the results of partial least squares (PLS) discriminant l’origine géographique est également observée et est confirmée par les analysis (88 % of correct classification). Similar evolutions and geographical résultats de l’analyse discriminante par les moindres carrés partiels (PLS) discriminations were obtained for specific physicochemical parameters. avec 88% de réponses correctes. Une évolution en fonction du temps et By PLS regression, good predictions of titratable acidity and sugar une discrimination géographique des baies sont également obtenues à partir concentration from berry spectral data were obtained, with root mean des données d’analyses physico-chimiques des moûts. À partir des données square error of prediction (RMSEP) of 0.53 g/L for titratable acidity spectrales, de bonnes prédictions des concentrations en sucres et de l’acidité (expressed in H2SO4) and 8 g/L for sugar concentration. Moreover, when titrable sont obtenues par régression PLS. Cependant, quand les données the data from only one of the regions were considered, the predictions of sont traitées séparément en fonction de l’origine géographique des titratable acidity and sugar concentration were improved and those of real échantillons (Touraine et Anjou), les prédictions des teneurs en sucres et acidity (pH) and maturity index were then satisfactory. The RMSEP values de l’acidité titrable sont améliorées et celles du pH et de l’indice de maturité for samples from Touraine and Anjou were reduced, respectively, to 0.05 sont alors satisfaisantes. and 0.02 units for pH, 0.4 and 0.12 g/L for titratable acidity (expressed in H2SO4), 6.6 and 3.2 g/L for sugar concentration, and 5 and 2.2 units for Conclusion : Les analyses des données spectrales MIR et physico- maturity index. chimiques conduisent à des résultats similaires. Les baies de raisin peuvent être caractérisées entre la véraison et la récolte en fonction du degré Conclusion: Spectroscopic and classic chemical analyses of grape berries d’avancement de la maturation et en fonction de l’origine géographique yielded highly similar results. The evolution of berries from “véraison” to des échantillons. Les régressions PLS établies entre les données spectrales harvest can be characterized according to both time course and region. The et physico-chimiques montrent que la spectroscopie moyen infrarouge est samples showed similar PCA results for chemical and IR spectra parameters. une bonne méthode pour prédire les évolutions des teneurs en sucre et PLS regression between chemical and spectral data showed that Fourier de l’acidité titrable des baies au cours de la maturation. Ces résultats, ainsi transform IR is a good method to predict acidity and sugar concentration que ceux de prédiction du pH, de l’indice de maturité et de la concentration throughout ripening. And the results for these parameters, as well as for en anthocyanes, sont améliorés si les régressions sont établies région par pH, maturity index and anthocyanin concentration, are improved if the région. En conséquence, une calibration est recommandée pour chaque regressions are calculated from sample sets restricted to a single growing groupe de baies de raisin en fonction de l’origine géographique. region. Consequently, a calibration model is required for each grape geographical origin. Impact de l’étude : Le potentiel du MIRS a été démontré pour la quantification des principaux indicateurs de maturité des baies de raisin. Significance and impact of the study: The potential of MIRS was De plus, ces spectres peuvent être utilisés pour estimer le niveau de maturité demonstrated for the quantification of the main indicators of maturity des baies en particulier en référence à une base de données spectrales établie during berry ripening. Furthermore, these spectra can be used to estimate sur plusieurs millésimes. L’association MIRS, chimiométrie et base de grape maturity in particular in reference to a spectral database established données pourra aider à suivre la maturation et à déterminer la date optimale over several years of study. The association infrared spectroscopy, de récolte. chemometric methods and database will help to monitor ripening and to determine the optimum harvest date. Mots clés : maturation, baies de raisin, spectroscopie moyen infra rouge, méthodes chimiques, corrélations Key words: ripening, infrared spectroscopy, chemical methods, correlations manuscript received the 6th July 2009 - revised manuscript received the 12nd October 2010 *Corresponding author: [email protected] - 219 - J. Int. Sci. Vigne Vin, 2010, 44, n°4, 219 - 229 ©Vigne et Vin Publications Internationales (Bordeaux, France) picque 24/12/10 14:15 Page 220 D. PICQUE et al. INTRODUCTION spectroscopic data and TSS, but the predictions of free amino nitrogen, malic acid, lactic acid and ethyl carbamate Reliable maturity indices and methods to objectively were not satisfactory. Dambergs et al. (2003) and Gishen evaluate grape quality are sought in order to monitor et al. (2005) confirmed that NIR spectroscopy to measure ripening, to determine the optimum harvest date and to TSS, acidity and colour (expressed as total anthocyanins) adapt winemaking practices to the desired wine styles. can be considered as a good predictor of red wine To assess grape maturity, various types of analyses are composition and quality. Arana et al. (2003) showed that carried out: i) the concentration of total soluble solids NIR reflectance technology is suitable to determine TSS (TSS, which is mainly a measure of sugars) and the acidity. content directly in the grape berries. Guggenbichler et al. This maturity is called the technological maturity. ii) (2006) established a fast quantitative analysis of the total phenolic compounds (TPC) and the total carbohydrates, total acidity, tartaric acid, malic acid, anthocyanins by spectrophotometric methods. This polyphenol content and pH of different grapes varieties maturity is called the phenolic maturity. Nevertheless, by NIR. These results were confirmed by Casiraghi et al. these parameters are admitted to be insufficient to assess (2007) who analysed samples collected during the last grape quality. Therefore, other analysis, such as aromatic period of ripening just before harvest. Local PLS profile by gas chromatography (Sanchez Palomo et al., regression (Dambergs et al., 2006) and artificial neural 2007), phenolic compounds by liquid chromatography networks (Janik et al., 2007) have been proposed as means (Pena-Neira et al., 2004), and sensory analysis (Rousseau of improving calibration performance mainly for the and Delteil 2003; Le Moigne et al., 2008) are used and prediction of anthocyanin concentrations. present a real potential. Unfortunately, these analyses are time consuming and are generally too expensive to be Herrera et al. (2003) made a first evaluation of a NIR considered by winemakers. spectrometer equipped with an optical fibre probe directly applied onto the berries. The Brix degree was estimated There is clearly a need to develop new methods to with an error of 1.06. Using two types of infrared sensors evaluate ripening of berries. The measurement of working by transmission or diffuse reflectance respectively mechanical properties of berries has made it possible to and allowing a direct measure on the berries or on the discriminate the « veraison » period, but no evolution grape bunches, Desseigne et al. (2003) obtained a good of different rheological parameters was found between correlation between infrared signals and TSS in grapes the “veraison” and the harvest periods (Robin et al., 1997, (coefficient of determination R2 = 0.90). Grotte et al., 2001). More recently, it has been shown that