Non-Saccharomyces wine yeast production in aerobic fed-batch culture

Barkhuizen, Jan-Harm Labuschagne (2015-12)

Thesis (MEng)--Stellenbosch University, 2015.

Thesis

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.

AFRIKAANSE OPSOMMING: Die produksie van die nie-Saccharomyces wyngiste Metschnikowia pulcherrima, Issatchenkia orientalis en Lachancea thermotolerans is geoptimaliseer in aerobiese gevoerde-lotkulture vir kommersiële toepassings. Hierdie nie-Saccharomyces wyngiste toon potensiaal wanneer hulle in kombinasie met Saccharomyces cerevisiae gebruik word om die organoleptiese eienskappe van die wyn te bevorder. Die hoofdoel van die projek was om die giste by ‘n maksimale biomassa-opbrengs (Yx/s) te produseer deur middel van aerobiese gevoerde-lotkulture waar ‘n dinamiese voermodel gebruik is om die kultuur by ‘n konstante spesifieke groeisnelheid (μspec) te handhaaf. ‘n Maksimum Yx/s van 0.83 g g-¹, 0.68 g g-¹ en 0.76 g g-¹ kon bereik word vir onderskeidelik I. orientalis, M. pulcherrima en L. thermotolerans deurdat die μspec by sleutelpunte gehandhaaf is tydens kulture by 9 L kon. Dit is hoër as die 0.51 g g-¹ wat in S. cerevisiae kulture bereik is. Wanneer L. thermotolerans op proefskaal (90 L) geproduseer is, is ‘n maksimum Yx/s van 0.54 g g-¹ bereik, wat noemenswaardig laer was as die 0.76 g g-¹ wat op klein skaal (9 L) bereik is. ‘n Sekondêre doelwit was om die gistingsprestasie van die gis te toets na afloop van die afsonderlike kulture. Die gistingsprestasie is getoets deur die aansuringsvermoë van die afsonderlike kulture te toets. Die gis se gistingsprestasie is verder getoets in sintetiese wyngisting. Die toetse het gewys dat die gis by ‘n groeisnelheid gekweek kan word waar ‘n maksimum biomassa-opbrengs bereik kan word sonder dat die werkverrigting tydens wyngisting benadeel word. Hierdie bevinding bevestig dat die giste by lae groeisnelhede gekweek kan word op kommersiële vlak. Die nie-Saccharomyces gis M. pulcherrima, I. orientalis en L. thermotolerans moet teen afsonderlike groeisnelhede van 0.10 h-¹, 0.11 h-¹ and 0.12 h-¹ produseer word om ‘n maksimale biomass opbrengs op suiker te lewer. By hierdie kondisies word die gistingsprestasie van die finale gis produk nie nadelig beïnvloed nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98010
This item appears in the following collections: