Corn starch gel for yeast cell entrapment. A view for catalysis of wine fermentation.

A new biocatalyst was prepared by immobilization of Saccharomyces cerevisiae AXAZ-1 yeast cells in the matrix of corn starch gel. This biocatalyst was used for repeated batch fermentations of glucose and grape must at various sugar concentrations (110-280 g/L) and low-temperature winemaking (5 degrees C). The biocatalyst retained its operational stability for a long period, and it was proved to be capable of producing dry and semisweet wines. The produced wines were analyzed for volatile byproducts by GC and GC-MS, and the results showed an increase in the number and amount of esters by immobilized cells. In addition, an increase in the percentages of esters and a decrease in those of alcohols with the drop of fermentation temperature were reported. The activation energy (E(a)) was lower (approximately 36%) and the reaction rate constant (k) was higher (approximately 78% at 30 degrees C and approximately 265% at 15 degrees C) in the case of immobilized cells compared to free cells, especially at low temperatures. These results show that corn starch gel may act as a promoter for the enzymes that are involved in the process or as a catalyst of the alcoholic fermentation and can explain the capability of immobilized cells for extremely low-temperature winemaking. Therefore, these results open a new way for research to find new catalysts in biotechnological processes.