Color Index For Red Grapes Research Articles

Comparative Study of Texture Properties, Color Characteristics, and Chemical Composition of Ten White Table-Grape Varieties

The texture, color, and chemical characteristics of 10 white table-grape varieties were compared: Delizia del Vaprio, Matilde, Moscato di Terracina, Panse precoce, Pizzutello bianco, Regina, Regina dei vigneti, Sublima seedless, Sultanina (or Thompson Seedless), and Vincere. Consumer acceptability of table grapes depends on such factors as visual attributes, chemical constituents, nutritive values, mechanical properties, and, obviously, sensory attributes, which are affected by the cultivar. Notable differences among the studied varieties were found in CIRG (color index of red grapes), solid soluble content, malic acid, hydroxycinnamic acid, and the amount of total polyphenols. However, the mechanical parameters of berries, as determined by texture profile analysis, and berry skin characteristics, evaluated by puncture testing, were the most important properties for the differentiation of varieties. In particular, PCA analysis indicated that hardness, gumminess, chewiness, break skin force, break skin energy, and Young's modulus of elasticity of skin were the best indices with which to characterize the varieties. These results may help viticulture and postharvest professionals recognize the behavior of each variety and thus better respond to the consumer market.

Effects of rootstocks and irrigation levels on grape quality of Vitis vinifera L. cv. Shiraz.

The influence of two rootstocks (SO4 and 1103P) on grape quality and berry chemical composition was studied in a factorial experiment, in field grown grapevines of cv. Shiraz (Vitis vinifera L.), subjected to five irrigation levels [0% (T1), 25% (T2), 50% (T3), 75% (T4) and 100% (T5) of irrigation depth (IW, mm): Class A pan evaporimeter (CPE)]. Spectrophotometric analyses of total anthocyanins (TA), total phenolics (TP) and total antioxidant activity (AA) in grape extracts were performed. Also, total soluble solids (TSS), total acidity, pH, total sugar content, ash, juice yield and color index of red grapes (CIRG) of berry samples were determined. TA, TP, AA, TSS, total sugar content, ash, and CIRG values decreased together with increasing irrigation levels. On the contrary, T4 and T5 irrigation treatments increased total acidity, pH and juice yield of samples compared to the effects of T1, T2 and T3 irrigation treatments for both rootstocks. Moreover, T1 or T2 treatments caused an increase in TA, TP, AA, TSS, total sugar content, ash, and CIRG index values of grape samples in comparison to that of vines irrigated with T3, T4 and T5 levels. Grape quality response to irrigation levels was altered by rootstocks and quality of grapes harvested from vines grafted on SO4 was higher compared to those from 1103P under all irrigation treatments. Based on the findings, it was suggested that T2 irrigation level might be sufficient to guarantee Shiraz yield potential without significant loss in grape quality under the study conditions. Also, the results make it possible to recommend use of SO4 rootstock under non-limiting water conditions because of its positive on grape quality parameters, while 1103P might be better choice under water-limiting conditions.

Assessment of Anthocyanins in Grape (Vitis viniferaL.) Berries Using a Noninvasive Chlorophyll Fluorescence Method

Anthocyanins (Anths) in grape (Vitis vinifera L.) berries harvested at véraison from Pinot Noir and Pinot Meunier cultivars were assessed nondestructively by measuring chlorophyll fluorescence (ChlF) excitation spectra. With increasing Anth content, less excitation light was transmitted to the deeper Chl layers, and thus the ChlF signal decreased proportionally. By applying Beer-Lambert's law, the logarithm of the ratio between the fluorescence excitation spectra (log FER) from a green and a red berry gave the in vivo absorption spectrum of Anths, which peaked at about 540 nm. Absolute quantitative nondestructive determination of Anths for each berry was obtained by the log FER calculated for two excitation wavelengths, 540 and 635 nm (absorbed and not-absorbed by Anths, 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 (r 2 = 0.92) using a power function. Reflectance spectra on the same berry samples were also measured, and Anth reflectance indices, which were originally developed for apples and table grapes, were derived. The log FER 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 log FER method, applied by means of suitable portable devices, may represent a new, rapid, and noninvasive tool for the assessment of grape phenolic maturity in vineyards.

Measuring the color of table grapes

This work attempts to determine objectively the external color of table grapes, examining a broad spectrum of white and red cultivars of different tints classified according to a descriptor of the OIV and using the CIELAB system. The pigment content and a color index for red grapes (CIRG), as defined in a previous study, are also analyzed. A statistical study reveals high linear correlations between the different parameters analyzed. The highest correlation was between the color index and the OIV-color. The color index used gave good results in the statistical differentiation of the sample groups considered. © 1996 John Wiley & Sons, Inc.