PEF treatments of high specific energy permit the reduction of maceration time during vinification of Caladoc and Grenache grapes
Introduction
Over the last decades, considerable research efforts have been devoted to the development of non-thermal processing technologies (Zhang, Barbosa-Cánovas, & Balasubramaniam, 2011). These technologies permit improving different unit operations in the food industry such as extraction providing more sustainable and eco-friendly processes (Chemat et al., 2017).
PEF technology is regarded as a promising alternative to thermal processing with the purpose of improving microbial inactivation (Wang et al., 2018), mass transfer (Puértolas, Luengo, Álvarez, & Raso, 2012), and structure modification (Oey, Faridnia, Leong, Burritt, & Liu, 2017). The treatment generates a high intensity electric field between two electrodes by applying pulses of high voltage and short duration. The effects of PEF on foods are attributed to a presumed structural rearrangement of the cell membranes called electroporation, which consists in the formation of local defects or pores (Kotnik, Rems, Tarek, & Miklavčič, 2019). The electroporation of grape skin cells with the purpose of improving the extraction of phenolic compounds during the maceration-fermentation step in red winemaking is one of the most widely investigated applications of PEF in recent years (Ricci, Parpinello, & Versari, 2018). Maceration is one of the most critical stages in red winemaking. During maceration, phenolic compounds that define many of the sensory attributes of red wine such as color, bitterness or astringency are transferred from the skins and seeds into the must (Bautista-Ortín, Busse-Valverde, López-Roca, Gil-Muñoz, & Gómez-Plaza, 2014; Busse-Valverde et al., 2010). Obtaining a wine with enough polyphenol content required that the solid parts of the grapes remain in contact with the fermenting must between 7 and 10 days. In order to increase its production capacity, wineries are interested in shortening the maceration time without affecting wine quality.
Different studies conducted in the laboratory, but also at pilot plant and semi-industrial scale, have demonstrated that PEF treatments can allow winemakers to reduce maceration time and/or obtain a wine with a greater amount of phenolic compounds (Puértolas, López, Condón, Álvarez, & Raso, 2010). In view of such effects, PEF could become an alternative to techniques such as thermovinification or flash release, currently used in wineries to improve polyphenol extraction based on the heating of grapes. Whereas thermovinification consists in heating grapes at temperatures between 70 and 75 °C for a period ranging from 30 min to 24 h (Sacchi, Bisson, & Adams, 2005), the process known as “flash release” consists in a rapid heating of grapes (85–95 °C) with direct steam injection, after which grapes are exposed to a vacuum that induces instant vaporization of the water they contain, thereby cooling them and weakening their skin cell envelopes (Moutounet & Escudier, 2000). After application of these techniques, solid parts of the grapes are removed after few hours of maceration and fermentation is conducted in liquid phase. The benefits of fermenting in liquid phase include a better use of the effective volume of the tanks, an improved control of fermentation temperature, and savings in labor as well as in the energy consumption required to periodically pump the wine over the skin mass that rises to the top of the fermentation tanks.
Although it has been demonstrated that electroporation of grape skins by PEF significantly improves the extraction of polyphenols such as anthocyanins and tannins, a certain maceration time is required to obtain wines with a sufficient amount of these compounds (López, Puértolas, Hernández-Orte, Álvarez, & Raso, 2009). Typical maceration times reported by different authors for wines obtained with grapes treated by PEF range from 3 to 6 days (Maza et al., 2019).
In the present study, intense PEF treatments in terms of specific energy were applied to electroporate grape skins of two grape varieties (Caladoc and Grenache) in order to evaluate whether the maceration step could thereby be reduced to just a few hours.
Section snippets
Grape samples
Seven hundred kilograms of Caladoc (21.1°Brix, titratable acidity: 6.1 g·L−1 tartaric acid) and Grenache (26.9° Brix, titratable acidity: 4.8 g·L−1 tartaric acid) red grapes (Fuendejalón, Spain) were manually harvested in 2018. Harvesting was carried out in the first week of September for Caladoc grapes and in the first week of October for Grenache grapes. Prior to the PEF treatments, electrical conductivity was measured with a FYA641LFP1 conductivity probe (Ahlaborn, Holzkirchen, Germany)
Effect of PEF treatments of different intensities on the extraction kinetics of color intensity, anthocyanins, and total phenolic compounds after different maceration times
The evolution of color intensity, anthocyanin content, and total phenolic compounds during the maceration-fermentation stage of Caladoc grapes treated by I-PEF after 4 and 24 h of maceration are shown in Fig. 1. The evolution of the same oenological indexes during maceration-fermentation of untreated and M-PEF treated Caladoc grapes after 10 and 4 days of maceration, respectively, is also shown in Fig. 1 for comparison. Considerable differences were observed between vinifications conducted with
Discussion
Polyphenol extraction during the maceration-fermentation step is a diffusion process in which the diffusion rate and extraction yield are both highly dependent on the integrity of grape skins' cytoplasmic membrane (Cerpa-Calderón & Kennedy, 2008; Pinelo, Arnous, & Meyer, 2006). Several investigations have demonstrated that the application of PEF treatments of very low energy (<10 kJ·kg−1) to grapes prior to the maceration-fermentation step can accelerate the extraction of polyphenols (Delsart
Conclusions
In this investigation, the potential of the application of PEF for obtaining red wine with a maceration time of only 24 h has been demonstrated for the first time. Although color intensity and anthocyanin content decreased significantly throughout fermentation when grape pomace was removed, oenological parameters of the wines after 3 months of bottling were similar and slightly lower than control wine in the case of Caladoc and Grenache wines, respectively.
Therefore, PEF could become an
CRediT authorship contribution statement
MAM carried out the experiments, interpreted the results, and wrote the first draft of the manuscript. CP and JMM carry out the experiments and conducted analysis. AC provided help for interpretation of the results. IA and JR were involved in the design of the study, interpretation of the results, and final writing of the manuscript.
Declaration of competing interest
Authors declare no conflict of interest.
Acknowledgments
M.M. gratefully acknowledges the Universidad Nacional de Cuyo, Argentina, for its financial support for his doctoral studies. Thanks likewise go to the European Regional Development Fund, to the Department of Innovation Research and University Education of the Aragon Government, and to the European Social Fund (ESF).
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