Anthocyanins (Anth) in grape (Vitis vinifera L.) berries harvested at véraison from Pinot Noir and Pinot Meunier cultivars were assessed non-destructively by measuring chlorophyll fluorescence (ChlF) excitation spectra. With increasing the Anth content, less excitation light was transmitted to the deeper Chl layers, and thus the ChlF signal decreased relatively. By applying the Beer-Lambert's law, the logarithm of the ratio between the fluorescence excitation spectra (logFER) from a green and a red berry gave the in vivo absorption spectrum of Anth, which peaked at about 540 nm. Absolute quantitative non-destructive determination of Anth for each berry was obtained by the logFER calculated for two excitation wavelengths, 540 and 635 nm (absorbed and not-absorbed by Anth, respectively) of ChlF at 685 nm. Over a range of skin colors going from green to purple, the relationship between the Log[ChlF(635)/ChlF(540)] and the Anth concentration of berry extracts was fairly well fitted (r2 = 0.92) using a power function. Reflectance spectra on the same berry samples were also measured and Anth reflectance indexes, which were originally developed for apples and table grapes, derived. The logFER Anth index was superior to the reflectance-ratio-based index, but was as good as the color index for red grapes (CIRG) calculated from the whole visible reflectance spectrum. The proposed logFER method, applied by means of suitable portable devices, may represent a new, rapid and non-invasive tool for the assessment of grape phenolic maturity in vineyards.
Assessment of Anthocyanins in Grape (Vitis vinifera L.) Berries Using a Noninvasive Chlorophyll Fluorescence method
Giovanni Agati;Paolo Matteini;
2007
Abstract
Anthocyanins (Anth) in grape (Vitis vinifera L.) berries harvested at véraison from Pinot Noir and Pinot Meunier cultivars were assessed non-destructively by measuring chlorophyll fluorescence (ChlF) excitation spectra. With increasing the Anth content, less excitation light was transmitted to the deeper Chl layers, and thus the ChlF signal decreased relatively. By applying the Beer-Lambert's law, the logarithm of the ratio between the fluorescence excitation spectra (logFER) from a green and a red berry gave the in vivo absorption spectrum of Anth, which peaked at about 540 nm. Absolute quantitative non-destructive determination of Anth for each berry was obtained by the logFER calculated for two excitation wavelengths, 540 and 635 nm (absorbed and not-absorbed by Anth, respectively) of ChlF at 685 nm. Over a range of skin colors going from green to purple, the relationship between the Log[ChlF(635)/ChlF(540)] and the Anth concentration of berry extracts was fairly well fitted (r2 = 0.92) using a power function. Reflectance spectra on the same berry samples were also measured and Anth reflectance indexes, which were originally developed for apples and table grapes, derived. The logFER Anth index was superior to the reflectance-ratio-based index, but was as good as the color index for red grapes (CIRG) calculated from the whole visible reflectance spectrum. The proposed logFER method, applied by means of suitable portable devices, may represent a new, rapid and non-invasive tool for the assessment of grape phenolic maturity in vineyards.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
