Vincenzo Gerbi

Influence of grape density and harvest date on changes in phenolic composition, phenol extractability indices, and instrumental texture properties during ripening.

Changes in the phenolic composition, phenol extractability indices, and mechanical properties occur in grape berries during the ripening process, but the heterogeneity of the grapes harvested at different ripening stages affects the reliability of the results obtained. In this work, these changes were studied in Nebbiolo grapes harvested during five consecutive weeks and then separated according to three density classes. The changes observed in chemical and mechanical parameters through the ripening process are more related to berry density than harvest date. Therefore, the winemaker has to select the flotation density according to the objective quality properties of the wine to be elaborated. On the other hand, the stiffer grapes were associated with a higher accumulation of proanthocyanidins. The harder grapes provided the higher concentration and extractability of flavanols reactive to vanillin, whereas the thicker ones facilitated the extraction of proanthocyanidins.

Varietal Comparison of The Chemical, Physical, and Mechanical Properties of Five Colored Table Grapes

The visual attributes of table grapes, their chemical constituents, and mechanical properties are involved in consumer acceptability because they are correlated to sensory perception. Usually, instrumental measurements are preferred to the sensory evaluations because they reduce variations in subjective judgments and can be carried out more easily. In this work, chemical-physical attributes and texture properties of five black table grapes (Alphonse Lavallée, Black magic, Cardinal, Perlon, Regina nera) were studied in order to identify significant varietal differences. Spectrophotometric and HPLC methods and texture analysis test were used to evaluate color index, sugars and acid composition, phenolic characteristics, and mechanical properties of the skin and the pulp of berries. Many differences were found among varieties in technological maturity indexes, hydroxycinnamic acid, anthocyanin content and profile, and relative CIE L*, a*, b* parameters, but the more relevant differences were found in mechanical properties. Principal component analysis showed that the texture profile analysis parameters (hardness, cohesiveness, gumminess, and resilience) and berry skin characteristics (break skin energy, skin modulus of elasticy) were the best indices able to fulfill the aim of this work. Almost all of the parameters showed differences among cultivars, confirming their importance in the characterization of the variety as well as in the assessment of potential consumer acceptability. In particular, the cultivars demonstrated different reactions to the compression test; thus, the texture analysis parameters can be appropriate to explain varietal differences and to allow their differentiation.

Influence of Different Thermohygrometric Conditions on Changes in Instrumental Texture Properties and Phenolic Composition during Postharvest Withering of ‘Corvina’ Winegrapes (Vitis vinifera L.)

‘Corvina’ winegrapes were postharvest withered under three controlled thermohygrometric conditions. Sampling was done on different days of withering and the mechanical properties, technological ripeness parameters, phenolic composition, and anthocyanin profile were determined. Depending on the condition, skin break force and pedicel detachment force significantly decreased during the dehydration process with a maximum variation of −0.258 and −1.306 N, respectively. Instead, total flavonoids of skin and seeds, and proanthocyanidins and low-weight flavanols of seeds increased, with a maximum variation of +1,483, +733, +1,022, and +469 mg/kg, respectively. The skin hardness was confirmed to be an important parameter for the dehydration kinetics.

Effect of growing zone and vintage on the prediction of extractable flavanols in winegrape seeds by a FT-NIR method.

The feasibility of Fourier transform-near-infrared (FT-NIR) spectroscopy for predicting the extractable content of phenolic compounds directly in intact grape seeds was evaluated. NIR calibration models were based on the correlation of spectral data with the phenolic composition determined by reference chemical methods for 40 grape samples. The vintage effect was studied evidencing that the predictive accuracy improved only for spectrophotometric indices when samples of two years were simultaneously considered. The statistical parameters of calibration showed that the models developed are sufficiently robust for quantitative purposes of total flavonoids, proanthocyanidins, low molecular weight flavanols, catechin, epicatechin, procyanidin B1, and galloylation percentage (standard prediction error (SEP%) < 15, predictive index (RPIQ) > 3.0), but could be also useful for screening of absorbance at 280 nm, total polymers, epicatechin gallate, and procyanidin B2 (SEP% < 15, RPIQ = 2.7-2.9). Although a calibration model is required for each geographical origin, the results suggest that FT-NIR spectroscopy is a promising analytical technique in this field.

Selection of a Mechanical Property for Flesh Firmness of Table Grapes in Accordance with an OIV Ampelographic Descriptor

Flesh firmness is a sensory characteristic proposed by Organisation Internationale de la Vigne et du Vin (OIV) as an ampelographic descriptor for grape varieties and Vitis species (OIV code 235). To accurately define the flesh firmness of table grapes, an instrumental texture parameter that makes it possible to classify the five reference table-grape cultivars according to this descriptor was selected. The mechanical properties of the berry flesh were determined by texture profile analysis and cutting tests. The results showed that the berry hardness and gumminess, normalized by berry diameter, are accurate instrumental indicators of flesh firmness because the variations among the cultivars were evident, independently of berry size and maturity grade. The interquartile ranges of berry hardness normalized by berry diameter for each flesh-firmness group established by OIV (soft, slightly firm, very firm) were 0.074 to 0.117, 0.121 to 0.158, and 0.205 to 0.391 N/mm, respectively. This standardized protocol can be applied to better compare the performance of grape varieties.

Use of instrumental acoustic parameters of winegrape seeds as possible predictors of extractable phenolic compounds.

The use of instrumental acoustic parameters produced during a compression test as reliable predictors of the extractable phenolic composition in intact winegrape seeds, determined by reference chemical methods, was evaluated by means of the analytical performance of calibration models. These models were developed only for those phenolic compounds most significantly and strongly correlated with the acoustic parameters. The analytical performance of the models was expressed in terms of standard error of cross-validation (SECV) and residual predictive interquartile amplitude (RPIQ), among other statistics. Several acoustic parameters showed satisfactory predictive accuracy for the percentage of galloylation in the terminal units, the content of (-)-epicatechin, and the mean degree of polymerization. Most of the reliable models developed are fairly recommended not for quantitative purposes but for fast screening (SECV% < 19, 1.6 < RPIQ < 2.1).

Application of enzyme preparations for extraction of berry skin phenolics in withered winegrapes

Postharvest withering of grapes strongly affects the content and extractability of phenolic compounds in the production of sfursat, fortified and passito wines. This work evaluated the effectiveness of enzymes applied individually and/or in multi-enzyme blends, on the extraction of anthocyanins, oligomeric flavanols and polymeric flavanols from withered grape skins during simulated maceration. The study was performed on Vitis vinifera L. cv. Nebbiolo and Barbera because of their different skin phenolic profile and cell wall composition. Our findings highlight that the relationship between skin mechanical properties (berry skin break force and energy) and extraction yield of phenolic compounds is variety dependent. Significant correlations were found between the skin softening associated with cell wall degradation and the extraction of anthocyanins and flavanols in Nebbiolo, for which polygalacturonase, individually or in multi-enzyme blends, plays an important role. In Barbera, the extractability of phenolic compounds was not affected by the presence of exogenous enzymes.