Use of pectinolytic yeast in wine fermentations

Abstract

The use of pectinolytic enzymes in winemaking is state of the art. These enzymes catalyse the degradation of pectic substances through depolymerization (hydrolases and lyases) and de-esterification. As a result, it supports the extraction of juice and facilitates filtration. It has also been shown in winemaking that the presence of pectinolytic enzymes improves the stability, taste, texture, colour and aroma of products. With regard to enzymes currently applied in winemaking, enzymes derived from filamentous fungi dominate the enzyme industry. Fungal-based pectinolytic enzymes specifically require purification from the culture medium to eliminate unwanted side reactions, which is poorly sustainable. Some non-traditional yeast strains have been reported to exhibit pectinolytic activities. Therefore, the direct use of pectinolytic yeast during wine fermentation process can be an attractive and alternative source for the use of enzymes as input. However, little is known about the effect of non-traditional yeasts with pectinolytic activities on wine fermentation and product quality. In fact, the use of such yeasts can have a very positive effect on the taste complexity and sensory richness of the product. In this study, from 17 different species more than 500 yeast strains were screened for their polygalacturonase activities (PGA). Enzymatic screening was performed in solid rich medium containing 2% polygalacturonic acid, and the activity of PGA+ strains was separately quantified with a microplate colorimetric test developed in this study. The superior pectinolytic yeasts were dominated by Kluyveromyces and Cryptococcus sp.. High pectinase producing Kluyveromyces sp (intrinsic yeast of grape must) was selected for further winemaking experiments. In particular, we investigated the consequences of the use of K. marxianus strains in sequential fermentation with S. cerevisae on fermentation kinetics, aroma profiles and more widely sensory properties of wines. Overall, the use of pectinolytic yeast in wine fermentations has the potential to benefit winemakers. In particular, hydrolysis of grape cell walls by K. marxianus endopolygalacturonase results in the release of compounds found in the skin of the grape that improve the quality of the wine.