Abstract

High energy consumption is often required to increase the extraction of phenolic compounds from grapes during alcoholic fermentation. Processes such as thermovinification require significant temperature changes over a long period of time to ensure the diffusion of phenolic compounds from the grape skin layer to the must. In this study, the capability of the ohmic heating (OH) process (E = 55 V/cm, t = 60–90 s, T = 72 °C) to improve the extractability of valuable intracellular compounds from grape skins of Aglianico and Barbera grape matrices before the alcoholic fermentation stepAs similarly reported by Donsì et al. (2010), any tissue damage to grape skins occurring after the application of either conventional or ohmic heating was not found to influence the rate of fermentation. was investigated and compared with both untreated and conventional thermally (CH) treated (T = 72 °C, t = 90 s) samples. Total phenolics and antioxidant capacity were monitored during fermentation (10 days). In comparison to the conventional thermal treatment, the results showed that the phenolic compound content of musts was twice as high immediately after OH treatment. This process could drastically improve the classic prefermentary maceration (thermovinifications, cold macerations, etc.) time. In finished wines produced from the treated musts, the total polyphenolic content of OH wines was up to 17 % higher than that of CH wines, and 30 % higher than that of untreated wines. No differences in concentrations of total tannins and anthocyanins were observed between conventional and ohmic heated musts. However, an increase of 30 to 200 % for some aromatic esters was observed in wines from ohmic heated musts. Overall, the outcomes of this work proved that, in addition to the thermal effect, the moderate electric field (MEF) applied during ohmic heating has the potential to induce an instantaneous release of polyphenolic compounds due to the electroporation phenomenon of cell membranes, thus saving energy and reducing processing time.

Highlights

  • From an oenological point of view, extracting phenolic compounds from grapes during the maceration/fermentation phase shows great interest

  • The capability of the ohmic heating (OH) process (E = 55 V/cm, t = 60–90 s, T = 72 °C) to improve the extractability of valuable intracellular compounds from grape skins of Aglianico and Barbera grape matrices before the alcoholic fermentation stepAs reported by Donsì et al (2010), any tissue damage to grape skins occurring after the application of either conventional or ohmic heating was not found to influence the rate of fermentation. was investigated and compared with both untreated and conventional thermally (CH) treated (T = 72 °C, t = 90 s) samples

  • The extraction potential of the ohmic heating treatment of grape must before alcoholic fermentation during the winemaking process was evaluated

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Summary

Introduction

From an oenological point of view, extracting phenolic compounds (e.g., anthocyanins, tannins and their polymers) from grapes during the maceration/fermentation phase shows great interest. The presence of these compounds determines the quality of red wines in terms of their structure, colour and mouthfeel, as well as theirbeneficial health properties (El Khawand et al, 2018). Only a fraction of the large amount of different phenolic compounds can be extracted using traditional winemaking techniques, with about 40 % of anthocyanins and 20 % of tannins from grape skins being transferred to the wine. This is because polyphenols and anthocyanins are mainly contained within the vacuoles of the hypodermal cells; their extraction encounters two main resistances to mass transfer in the form of the vacuole membrane and the cell membrane respectively (Donsì et al, 2010)

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