Aplicación de tecnologías no térmicas (ultrasonidos y microondas) en enología

Abstract

In the last decade, the winemaking industry has experienced significant advances in the use of non-thermal technologies, such as high-power ultrasound (US), thanks to the approval of its use by the International Organisation of Vine and Wine, although other technologies such as microwaves continue to be studied. The main objective of these technologies is to accelerate the extraction of compounds of interest during maceration in red wines by breaking down the cell walls that act as diffusion barriers, responding to the logistical needs of wineries and the challenge of climate change. Despite the advances, most of the tests carried out so far have been limited to the laboratory scale, so it is essential to study these technologies on a semi-industrial and industrial scale, which can be extrapolated to the winery. This Doctoral Thesis focuses on investigating the capacity of high-power ultrasound to accelerate the extraction of compounds, especially phenolics, during the maceration of red wines by breaking the cell walls, and also analyses the extractive effect of microwaves, an emerging technology in oenology, using semi-industrial-scale ultrasound device, as well as a laboratory scale microwave system. The results obtained show that the application of US on crushed grapes causes alteration of the cell walls, affecting their morphology, generating ruptures and facilitating the release of intracellular content. This effect varies according to the treatment conditions, with the use of low frequencies being better in the case of seeking a greater extraction of phenolic compounds. Furthermore, it was observed that the use of US increases the colour intensity and the concentration of phenolic compounds in red wines with the same maceration time (7 days) and also allows obtaining wines with chromatic characteristics similar to traditional maceration methods, but in a shorter time (3 days). Tests carried out on less-than-optimal grapes (with low sugar content and phenolically immature or partially botrytised) showed that the use of US leads to wines of high organoleptic quality with a lower alcohol content, without any undesirable sensory characteristics. In addition, comparisons were made with pectolytic enzymes, traditionally used in winemaking for the same purpose. The results indicated that the use of US allows a higher extraction of compounds compared to enzymes. However, the combination of the application of US and the subsequent addition of enzymes showed a synergistic effect, resulting in wines of higher phenolic quality compared to the use of the techniques separately. It is important to note that the effect of the US varies according to the grape variety, as the structural and compositional differences in the cell walls resulted in differences in the extraction of phenolic compounds, depending especially on the amount of cell wall in the grape. As for the use of microwaves on crushed grapes, an increase in the extraction of phenolic compounds, such as anthocyanins, flavonols, phenolic acids and tannins, was observed with a shorter maceration time. This allowed for a reduction in winemaking time and improved colour stability of the wines. In summary, this PhD Thesis demonstrates the benefits of using high power ultrasound and the potential of microwaves as tools to enhance the extraction of compounds of interest in wine production, not only reducing processing times, and, therefore, increasing winery productivity, but also improving wine quality.