Influence of yeast flocculation on the rate of Jerusalem artichoke extractfermentation

Variations in residual sugar composition have been observed during Jerusale m artichoke extract fermentations by using Saccharomyces diastaticus NCYC 6 25, a flocculating yeast strain. In batch cultures, these differences were due to the inulin polymer size distribution of the extracts: measurements o f enzymatic activities on different polymerized substrates have shown that the hydrolysis and ft fermentation yield decreased when the fructose/glucos e ratio of the extract increased. Inulin hydrolysis appealed to be the limi ting factor of the fermentation rate. A comparison of continuous and batch cultures with the same extract showed that fermentability differences were related to the structure and size of the yeast flocs. This led to an hydrol ysis selectivity of the inulin polymers according to their size: the chemos tat culture in which the flee average size was larger gave longer chained r esidual sugars.