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OATAO is an open access repository that collects the work of some Toulouse researchers and makes it freely available over the web where possible. This is an author's version published in: https://oatao.univ-toulouse.fr/22836Official URL : https://doi. AbstractSeveral studies have shown that the reserve disaccharide trehalose also protects yeast cells under environmental stress. Besides, it is acknowledged that trehalose improves yeast viability so its synthesis has become paramount in baker's yeast industry, as well as in wine and beer production. In this work, starving carbon or nitrogen conditions were imposed to Saccharomyces cerevisiae growing in fed-batch cultivations in order to induce biosynthesis and accumulation of trehalose. Our experimental results show that yeast can accumulate trehalose up to 13% of biomass dry weight (0.13 g trehalose g −1 ) under carbon or nitrogen starvation. A compartmentalized and biochemically structured model is proposed in order to mathematically describe these experimental findings. The model predictions were compared with literature results obtained under growth conditions different from those established in our experiments, resulting in a very good agreement and thus indicating that the proposed hypotheses are essentially correct.

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Growth and enzymes production by Aspergillus flavipes FP-500 were evaluated on pectin, polygalacturonic acid, galacturonic acid, arabinose, rhamnose, xylose, glycerol and glucose at different initial pH values. We found that the strain produced exopectinases, endopectinases and pectin lyases. Exopectinases and pectin lyase were found to be produced at basal levels as constitutive enzymes and their production was modulated by the available carbon source and pH of culture medium and stimulated by the presence of inducer in the culture medium. Endo-pectinase was basically inducible and was only produced when pectin was used as carbon source. Our results suggest that pectinases in A. flavipes FP-500 are produced in a concerted way. The first enzyme to be produced was exopectinase followed by Pectin Lyase and Endo-pectinase.

Kinetic studies are presented for xylitol production and growth of the yeast Candida parapsilosis ATCC 28474. The oxygen supply in¯uence on xylitol production from xylose was investigated. No metabolic activity was detected in anaerobic conditions. In contrast, it was found that under low aeration rates (0.1±0.2 vvm), xylitol is produced. Xylitol production decreases when air ow to reactor is augmented. An unstructured model is proposed for the kinetic behaviour analysis of yeast growing in batch culture. A simplex method was used for the estimation of model parameters. The parameter con®dence intervals were also calculated. List of symbolsVector of model constant terms dim(b) = m  1 dc L