Aim: This work evaluates the effects of the combined use of heat treatment (HT, 75 °C, 2 min) and proteases (P) on the protein stability and volatile composition of two white wines, obtained from the Greek cv. Assyrtiko and Moschofilero. Methods and results: Wine protein stabilization was assessed by heat test, using RP-HPLC determination of pathogenesis-related proteins (PRP) and by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The impact of bentonite and P + HT treatment on wine aroma profile was evaluated by GC-MS with liquid-liquid extraction. According to the heat test, in Assyrtiko wine the level of stability achieved with P + HT was comparable with that obtained by bentonite fining and for Moschofilero wine -where protein instability was higher -bentonite was more efficient. RP-HPLC profiles showed that, in general, higher percentages of chitinases (CH) than thaumatin-like proteins (TLP) were removed by both bentonite and P + HT, with a similar efficiency for the two treatments and sometimes better performances for the latter. Conversely, TLP were removed more efficiently by bentonite, even if some fractions were eliminated to a slightly higher extent by proteases. In the conditions of the experiment, bentonite resulted in minor changes to the wine aroma profile. However, heating during protease treatment modified wine volatile composition, reducing the concentration of esters produced during fermentation while simultaneously increasing the contents of certain esters characteristic of aging such as ethyl lactate. Conclusions: The combination of proteases and heat treatment may be a promising technique for protein stabilization of wines. However, further investigations are needed to optimize the time:temperature ratio of the heat treatment in order to obtain the maximum protease activity and the minimum thermal deterioration of the wine quality. Significance and impact of the study: The results of this study have a practical interest for both the scientific community and wine sector, contributing to knowledge of the efficacy and limitations of the use of protease enzymes for wine stabilization.Assyrtiko, bentonite fining, Moschofilero, protease, protein stability, wine aroma

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23Ribolla Gialla (RG) is a white grape variety used in the production of high-quality sparkling 24 wines. It is widespread in North-East Italy, particularly Friuli Venezia Giulia (FVG), as well as 25 Slovenia. Because of its limited area of cultivation, however, there is little information about 26 the composition and chemical characteristics of the sparkling wines produced. This work used 27 different analytical approaches to characterize thirty-three commercial sparkling RG wines 28 from different areas of FVG. The characteristics included the overall volatile profile and content 29 of terpenes, C 13 -norisoprenoids, lipids, and tryptophan metabolites. The aroma profile of RG 30 wines was mainly characterized by fermentative esters and β-damascenone, whereas other 31 norisoprenoids and varietal aromas were below the odor threshold. Appreciable amounts of 32 certain fatty acids were found (e.g., palmitic acid), which could be potentially correlated with 33 greater foam stability. However, high concentrations of tryptophan metabolites highlighted a 34 higher risk of developing atypical ageing defects.

Depending on the vineyard location, cluster thinning (CT) may represent an effective tool to obtain the desired grape composition and wine quality. The effect of 20% cluster thinning on Ribolla Gialla (Vitis vinifera L.) sparkling wine aroma, lipid compounds, and aromatic amino acid (AAA) metabolites composition was studied for three consecutive seasons in two vineyards located in the Friuli Venezia Giulia region, Italy. In the examined sparkling wines, the vintage meteorological conditions exhibited significant influences on the metabolic profile of the samples. Data were normalized by season, and the impact of the CT treatment was evaluated for each vineyard site separately. Crop removal showed a limited positive impact on aroma compounds in sparkling wines from vineyards located in the valley. Concerning the AAA compounds, their concentration was higher in the vineyard at the foot of the hills. Cluster thinning resulted in a drop in concentration, reducing the risk of atypical aging. Despite minor differences according to targeted metabolome profiling, the sensory analysis confirmed the effects of the CT treatment in the valley floor vineyard. Reducing crop in this site, where the yield was higher, promoted a moderate improvement of Ribolla Gialla sparkling wine. In contrast, for wine produced in the vineyard at the foot of the hills, the sensory analysis indicated a preference for wines from the unthinned control samples. Overall, the study indicates that cluster thinning is a viticultural technique that could potentially improve the quality of Ribolla Gialla sparkling wines, but only in situations of excessive grape production.

Pulsed electric field (PEF) is a non-thermal technology able to promote color and polyphenols extraction from grape skins. Most of the publications about PEF in winemaking report data concerning international varieties, poorly considering minor cultivars and the medium/long-term effects of the treatment on wine composition during storage. PEF was applied at different specific energies (2, 10, and 20 kJ kg−1) on grapes of the low-color red cv. Rondinella, after crushing-destemming. Pressing yield, the evolution of color, and total phenolic index (TPI) were measured during skin maceration. Moreover, the wines were characterized for basic compositional parameters, color, anthocyanin profile, phenolic composition (glories indices), metal content (Fe, Cr, and Ni), and sensory characters, two and twelve months after the processing, in comparison with untreated samples and pectolytic enzymes (PE). PEF did not affect fermentation evolution, nor did it modify wine basic composition or metal content. Treatments at 10 and 20 kJ kg−1 led to higher color and TPI in wines, in comparison to PE, because of increased content of anthocyanins and tannins. The sensory evaluation confirmed these findings. Modifications remained stable in wines after twelve months. Glories indices and vitisin A content highlighted greater potential stability of wine color in PEF-treated wines.