Wine production by novel yeast biocatalyst prepared by immobilization on watermelon (Citrullus vulgaris) rind pieces and characterization of volatile compounds

A novel yeast biocatalyst was prepared by using watermelon pieces as immobilizing support for yeast, Saccharomyces cerevisiae 101 strain for use in wine production. Immobilization was confirmed by electron microscopy. Suitability of biocatalyst was investigated by using it in repeated batch and continuous fermentations. The fermentation rate and other parameters were compared with free yeast cells at different temperatures. In all cases fermentation time was short (22 h at 30 °C and 80 h at 15 °C) and ethanol productivities were high (4 g/l/h). The volatile compounds, methanol, ethyl acetate, propanol-1, isobutanol and amyl alcohols that formed during fermentation were analyzed with the help of GC-FID. The concentrations of ethyl acetate and methanol were not more than 100 mg/l in all cases, indicating an improvement in the product. Cell metabolism of immobilized yeast was not much affected by immobilization. It was found that the immobilization of yeast on watermelon pieces increased the fermentation rate, vitality and viability of yeast cells. Preliminary sensory tests established the fruity aroma, fine taste and the overall improved quality of the produced wines.