Fabrizio Torchio

Mechanical properties, phenolic composition and extractability indices of Barbera grapes of different soluble solids contents from several growing areas

Phenolic compounds, extractable from grape skins and seeds, have a notable influence on the quality of red wines. Many studies have clearly demonstrated the relationship between the phenolic composition of the grape at harvest time and its influence on the phenolic composition of the red wine produced. In many previous works the evolution of phenolic composition and relative extractability was normally studied on grapes sampled at different times during ripening, but at the same date the physiological characteristics of grape berries in a vineyard are often very heterogeneous. Therefore, the main goal of the study is to investigate the differences among mechanical properties, phenolic composition and relative extractability of Vitis vinifera L. cv Barbera grape berries, harvested at the same date from several vineyards, and calibrated according to their density at three levels of soluble solids (A=235+/-8, B=252+/-8 and C=269+/-8 g L(-1) sugar) with the aim of studying the influence of ripeness stages and growing locations on these parameters. Results on mechanical properties showed that the thickness of the berry skin (Sp(sk)) was the parameter most affected by the different level of sugars in the pulp, while different skin hardnesses, evaluated by the break skin force (F(sk)), were related to the cultivation sites. The latter were also observed to influence the mechanical characteristics of seeds. Generally, the anthocyanin content increased with the level of soluble solids, while the increase in the tannin content of the berry skin and seeds was less marked. However, significant changes in flavanols reactive to vanillin in the seeds were found. The cellular maturity index (EA%) was little influenced by the soluble solids content of grapes.

Candida zemplinina can reduce acetic acid produced by Saccharomyces cerevisiae in sweet wine fermentations

ABSTRACT In this study we investigated the possibility of using Candida zemplinina, as a partner of Saccharomyces cerevisiae, in mixed fermentations of must with a high sugar content, in order to reduce its acetic acid production. Thirty-five C. zemplinina strains, which were isolated from different geographic regions, were molecularly characterized, and their fermentation performances were determined. Five genetically different strains were selected for mixed fermentations with S. cerevisiae. Two types of inoculation were carried out: coinoculation and sequential inoculation. A balance between the two species was generally observed for the first 6 days, after which the levels of C. zemplinina started to decrease. Relevant differences were observed concerning the consumption of sugars, the ethanol and glycerol content, and acetic acid production, depending on which strain was used and which type of inoculation was performed. Sequential inoculation led to the reduction of about half of the acetic acid content compared to the pure S. cerevisiae fermentation, but the ethanol and glycerol amounts were also low. A coinoculation with selected combinations of S. cerevisiae and C. zemplinina resulted in a decrease of ∼0.3 g of acetic acid/liter, while maintaining high ethanol and glycerol levels. This study demonstrates that mixed S. cerevisiae and C. zemplinina fermentation could be applied in sweet wine fermentation to reduce the production of acetic acid, connected to the S. cerevisiae osmotic stress response.

Exploitation of the non-Saccharomyces yeast Starmerella bacillaris (synonym Candida zemplinina) in wine fermentation: Physiological and molecular characterizations

Nowadays, the use of non-Saccharomyces yeasts in combination with Saccharomyces cerevisiae is a state-of-the-art strategy to improve complexity and enhance the analytical composition of the wines. This application has stimulated the interest of understanding how the non-Saccharomyces yeasts can contribute to the quality of the wines. The study presented here explores the potential use of Starmerella bacillaris (synonym Candida zemplinina) under winemaking conditions. Physiological and genetic characterizations of sixty-three isolates of Starm. bacillaris, previously isolated from four different varieties of grapes, were carried out. Both analyses revealed a low level of diversity between the isolates of Starm. bacillaris, while the fermentation trials in laboratory scale demonstrated the good enological performance of this species. The strong fructophilic character of this species and its ability to produce low quantities of ethanol and acetic acid and high amounts of glycerol were confirmed. The results, presented here, demonstrated a potential application of this non-Saccharomyces species in mixed wine fermentations with S. cerevisiae.

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.

Influence of Wine-Grape Skin Hardness on the Kinetics of Anthocyanin Extraction

The main aim of this work was to study in a model, hydroalcoholic solution containing 12% of ethanol and with a pH of 3.20, the kinetics of anthocyanin extraction from Vitis vinifera L. cv. Nebbiolo berries of different skin hardness. This mechanical property was evaluated as the breaking skin force measured by Texture Analysis, a rapid and low-cost analytical technique. Using a TAxT2i Texture Analyzer, a puncture test was carried out on two groups of berries separated according to their density by flotation in order to obtain more homogenous samples and minimize the effect of different stages of ripening of the berries. Among the berries containing 242 ± 8 g/L of reducing sugars in the pulp juice, two groups of berries with different skin hardness were selected: soft (0.26 ± 0.04 N) and hard (0.47 ± 0.05 N). In our experimental conditions, at the end of maceration, the extracts from the higher skin hardness group showed the higher contents of total anthocyanin: +25 mg/L (+9.4%). The anthocyanin profile of extracts, obtained at different extraction times, showed no significant differences among the distribution of different anthocyanins. Only in the early phases of dissolution, did the extracts reveal a dissimilar anthocyanin profile and in the extracts of hard skins higher percentages of cyanidin and peonidin derivatives were present. Additionally, the evolution of skin mechanical properties from veraison to overripe and the influences of biotype on these parameters at harvest are reported in this work.

Assessment of Physicochemical Differences in Nebbiolo Grape Berries from Different Production Areas and Sorted by Flotation

In vineyards, in-field grape variability attributable to environmental factors can induce differences in the ripening process and, therefore, in the physicochemical characteristics of grape berries. This variability is often higher among different growing locations. Automatic, densimetric berry-sorting machines have recently been developed and proposed for use in wineries to reduce this variability, thereby making grapes uniform in terms of density. Densimetric sorting requires the selection of a density value according to objective quality parameters of the berries. The aim of this work was to determine the relationships among different objective quality parameters of Nebbiolo grapes harvested on the same date, such as mechanical properties, phenolic composition, and extractability indices; to determine the berry density estimated by flotation in different salt solutions of densities ranging from 1069 to 1125 kg m−3; and to investigate the influence of the growing location on these relationships. The results revealed that the most promising physicochemical parameters for determining the appropriate density are the total anthocyanin and flavonoid concentrations in the skins, the total flavonoid and oligomer proanthocyanidin contents in the seeds, and skin hardness and thickness. Nevertheless, density selection must be performed for each individual vineyard or homogeneous group of vineyards belonging to the same production zone because the correlation of berry density with these parameters also depends on the vineyard effect. Densimetric sorting of berries can be used to separate grapes with different quality parameters.

CIEL *a *b * parameters of white dehydrated grapes as quality markers according to chemical composition, volatile profile and mechanical properties

In the oenological sector, the withering process is of particular importance in the production of dry and sweet dessert wines due to the total or partial use of overripe and/or dehydrated grapes. This complex process leads to several changes in the chemical-physical characteristics of white grape berries affecting the wine quality and, at the end of the dehydration period, different visual attributes are usually present in the berry skins. The aim of this work, therefore, was to study the properties of Erbaluce dried grapes of varying external colors, classified into three groups based on reflectance colorimetry (green, gold and blue). The chemical composition, volatile profile and mechanical attributes were investigated, focusing on establishing relationships between CIEL*a*b* parameters of dehydrated grapes and their chemical-physical characteristics. The higher values of the glucose-fructose ratio, together with the higher content of sugars, gluconic acid and glycerol, but lower titratable acidity, suggests the presence of Botrytis cinerea Pers. infection in blue withered berries, which has been microbiologically confirmed. Regarding the instrumental mechanical properties, blue dehydrated grapes were characterized by a lower skin hardness and higher skin thickness in agreement with the higher weight loss experienced. Finally, the determination of free and bound volatile compounds showed that some of them were only found in blue withered berries, δ-lactones being considered the main chemical markers of the noble rot infection that are important for the odor character. C-10 alkyl massoia lactone was the most abundant volatile compound in blue botrytized grapes.

Comparative study of the resveratrol content of twenty-one italian red grape varieties

The content of resveratrol and some related stilbenes (piceids and piceatannol) in 21 Italian red grape varieties growing in the same edapho-climatic conditions and at the same stage of ripening was measured. Some varieties, like Barbera, Schiava gentile, Corvina and Marzemino, showed a trans-resveratrol content in the skin two to three times higher than the average content of all varieties. Trans- and cis-piceids were found in concentration higher than that of resveratrol, confirming both to be important contributors to the pool of health-promoting molecules present in grapes. Considering the total amount of stilbenes, the highest content was found in Barbera, Franconia, Negroamaro, Corvina and Marzemino, whereas other varieties, such as Montepulciano, Dolcetto, Croatina, Refosco and Primitivo, seem to synthesise very low amounts of these compounds. Barbera grapes also contain a relatively high concentration of transpiceatannol, a stilbene with even higher antioxidant properties than resveratrol, which means that it could be an interesting variety as a source of health-promoting molecules.

Investigating the use of gradient boosting machine, random forest and their ensemble to predict skin flavonoid content from berry physical-mechanical characteristics in wine grapes

Texture properties and flavonoids content were measured in 22 wine-grape cultivars.Regression trees, random forests and gradient boosting machine were applied to data.Variance explained by those models was very high in external and internal validation.Model performances will be further increased by cultivar-specific calibrations. Flavonoids are a class of bioactive compounds largely represented in grapevine and wine. They also affect the sensory quality of fruits and vegetables, and derived products. Methods available for flavonoid measurement are time-consuming, thus a rapid and cost-effective determination of these compounds is an important research objective. This work tests if applying machine learning techniques to texture analysis data allows to reach good performances for flavonoid estimation in grape berries.Whole berry and skin texture analysis was applied to berries from 22 red wine grape cultivars and linked to the total flavonoid content. Three machine-learning techniques (regression tree, random forest and gradient boosting machine) were then applied. Models reached a high accuracy both in the external and internal validation. The R2 ranged from 0.75 to 0.85 for the external validation and from 0.65 to 0.75 for the internal validation, while RMSE (Root Mean Square Error) went from 0.95mgg-1 to 0.7mgg-1 in the external validation and from 1.3mgg-1 to 1.1mgg-1 in the internal validation.

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.