Browsing by Author "Barkhuizen, Jan-Harm Labuschagne"
Now showing 1 - 1 of 1
Results Per Page
- ItemNon-Saccharomyces wine yeast production in aerobic fed-batch culture(Stellenbosch : Stellenbosch University, 2015-12) Barkhuizen, Jan-Harm Labuschagne; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: The production of the non-Saccharomyces wine yeasts Metschnikowia pulcherrima, Issatchenkia orientalis and Lachancea thermotolerans was optimised in aerobic fed-batch cultures for commercial application. These non-Saccharomyces have been used in sequential wine fermentations where they are employed to enhance the organoleptic characteristics of wine. The primary goal was to produce these organisms at a maximum biomass yield (Yx/s) through aerobic fed-batch cultivations where a dynamic feed regime was used to ensure accurate control over the specific growth rate (μspec) of each culture. By controlling the μspec at preferred points during cultivation at 9 L scale, Yx/s maxima of 0.83 g g-¹, 0.68 g g-¹ and 0.76 g g-¹could be achieved for I. orientalis, M. pulcherrima and L. thermotolerans, respectively. This was higher than the 0.51 g g-¹ achieved in Saccharomyces cerevisiae cultures, due to the Crabtree-positive behaviour of the latter. When producing L. thermotolerans at 90 L pilot scale a maximum Yx/s of 0.54 g g-¹ was achieved, which was significantly lower than the 0.76 g g-¹ achieved at 9 L bench scale. A secondary goal was to determine what effect different production growth rates has on the culture’s subsequent fermentative performance or yeast quality. The fermentative performance of the yeasts produced under various culture conditions were evaluated by measuring the acidification power of the yeast and evaluating the yeast in synthetic wine fermentations. The tests indicated that the yeast can be produced at a growth rate where the Yx/s is at a maximum value without compromising the quality of the yeast culture. This allowed the selection of conditions where a maximum Yx/s is produced for industrial yeast production. The non-Saccharomyces yeasts M. pulcherrima, I. orientalis and L. thermotolerans should be produced at 0.10 h-¹, 0.11 h-¹ and 0.12 h-¹, respectively. These growth rates will ensure the highest possible biomass yield on sugar with any compromise to the fermentative performance of the yeast product.