Grape pomace fermentation and cell wall degradation by Kluyveromyces marxianus Y885

Abstract

Kluyveromyces marxianus Y885, an endopolygalacturonase (EPG) producing yeast, was evaluated for its capacity to hydrolyse the cell wall polymers of grape pomace as well as its general fermentation capabilities on this substrate. Small scale batch fermentations on autoclaved pomace inoculated with Y885 delivered 10 g/l ethanol and 7.7 g/l glycerol, the latter 14% more than a commercial wine yeast strain. When comparing the hydrolysis of the pomace cell wall by the Kluyveromyces EPG with that of a commonly used pectolytic commercial enzyme preparation, the polymer analysis confirmed that both the Y885 EPG and the commercial enzyme preparation primarily degraded surface exposed pectin polymers, while the hemicellulose-cellulose backbone was unchanged. High levels of galacturonic acid (GalA) monomers were generated by the commercial enzyme, whereas the Y885 EPG mostly liberated (polymeric) GalA-containing fragments together with low quantities of monomers. The Y885 strain produced strong pectinase activity throughout the fermentation process, whereas pectinolytic activity levels rapidly declined for the commercial enzyme after addition. The data obtained shows the evolution of pectin degradation during fermentation and provide compelling evidence that Y885 can utilise/valorise the grape pomace, and that the secreted enzymes (including an EPG) can effectively unravel the structural components of the grape cell walls.