Study of the alcoholic fermentation of must stabilized by pulsed electric fields - effect of SO2

Resum

Pulsed electric field (PEF) technology has been used to preserve fruit juice and to delay spoilage by microorganism. In vinification, sulphur dioxide (SO2) is used as antimicrobial and as antioxidant. The aim of this study was to assess the effect of the sulphur dioxide content on the nitrogen metabolism (consumption of amino acids and formation of biogenic amines) and the production of volatile compounds throughout the alcoholic fermentation of must processed by PEF. Taking advantage of the fact that PEF treatments allow reducing the level of sulphur dioxide and, at the same time, guarantee the biochemical and microbiological stability of the must this study could be a starting point leading to an effective reduction of the sulphur dioxide content in wines. For this purpose, must of Vitis vinífera var. Parellada was stabilized by a PEF treatment and inoculated with Saccharomyces cerevisiae Na33 strain. The fermentations were carried out with and without SO2. From the results obtained, it was observed that the PEF treatment led to four logarithmic reductions of the microbial population of Parellada must without modifying the content of fatty acids and free amino acids of Parellada grape juice, which are essential for the development of the yeast during fermentation. As far as the development of the wine alcoholic fermentation is concerned, results showed that yeast consumed preferably the amino acids in the first half of fermentation in presence of SO2. The final concentration of amino acids in the wines obtained using PEF was greater when the must fermented without SO2 than when the latter compound was present. Therefore, it could be stated that the presence of SO2 facilitated the consumption of amino acids and, hence, the wine may have higher microbiological stability than that obtained from fermentation without SO2. Regarding the biogenic amines, they were mainly synthesized after the consumption of the first 25% of sugars and their formation was qualitative and quantitatively low. The SO2 concentration did not affect the formation of biogenic amines during the alcoholic fermentation. On the other hand, the evolution of the volatile compounds profile throughout the fermentations with and without SO2 was similar. The content of volatile acids in the wine obtained using SO2 was not significantly different than that fermented without adding this compound. However, the final content of total alcohols and esters were different even thought the differences were small. Consequently, when grape must was treated by PEF, the SO2 concentration usually used in winemaking could be reduced to safer levels or even eliminated without an important effect on the volatile compounds content of the final product. Therefore absence of SO2 should not have a negative impact on sensory characteristics of wine. © 2008 by Nova Science Publishers, Inc. All rights reserved.