A four-year comparison of the assessment of anthocyanins in berries (Vitis vinifera L. cv. Pinot noir) using a non-invasive chlorophyll fluorescence method

Abstract

The aim of this study was to find a method assessing non-destructively the maturity and anthocyanin concentration of Vitis vinifera L. cv. Pinot noir providing a tool to better estimate the variability within a vineyard. Besides the CIELa*b* using the visible reflectance spectrum and hyperspectral imaging (combining short- wave-infrared (SWIR) images and vis/NIR images), a hand-held optical sensor (Multiplex3® (Force-A, Orsay, France) based on chlorophyll fluorescence screening showed promising results. Indeed, a relationship between the Multiplex3 index and the anthocyanin concentration was already shown. However, whether this relationship is stable over different ripening seasons has not been proven yet. Grapes of Pinot noir (planted in 2003 and grafted on SO4 rootstock) were collected at different phenological stages over four ripening seasons (2011-2014) at Geisenheim (Germany). The berries were segregated according to their density using a flotation method to avoid discrepancies in sugar concentration. After sorting, Multiplex3® measurement were applied. To assess anthocyanin concentration the “Harbertson- Adams” method was used in berry skin and compared to the “Iland” method for anthocyanins in homogenates. A fairly good correlation was found between the two methods (R2=0.92). Marked differences between the seasons were observed and it seemed that anthocyanins accumulation was increased by warmer conditions during the ripening stage. The Multiplex3® chlorophyll index (SFR_R) was inversely linearly correlated to the total soluble solids (°Brix). Furthermore the Multiplex3® anthocyanins index (FERARI) was correlated with the concentration of anthocyanins (R2=0.91). Even better results were obtained when analyzing the years separately. The correlations were validated with randomly selected and representative berry samples and compared to measurements on bunches measured in the field.