The influence of yeast oxygenation prior to brewery fermentation on yeast metabolism and the oxidative stress response

Abstract

Yeast preoxygenation can confer important advantages to brewery fermentations by means of omitting the need to oxygenate the wort. However, the impact of yeast preoxygenation on yeast metabolism has never been assessed systematically. Therefore, expression analysis was performed of genes that are of importance in oxygen-dependent pathways, oxidative stress response and general stress response during 8 h of preoxygenation. The gene expressions of both the important transcription factors Hap1 and Rox1, involved in oxygen sensing, were mainly increased in the first 3 h, while YAP1 expression, which is involved in the oxidative stress response, increased drastically only in the first 45 min. The results also show that stress-responsive genes (HSP12, SSA3, PAU5, SOD1, SOD2, CTA1 and CTT1) were induced during the process, together with the accumulation of trehalose. The accumulation of ergosterol and unsaturated fatty acids was accompanied by the expression of ERG1, ERG11 and OLE1. Genes involved in respiration (QCR9, COX15, CYC1 and CYC7) also increased during preoxygenation. Yeast viability did not decrease during the process, and the fermentation performance of the yeast reached a maximum after 5 h of preoxygenation. These results suggest that yeast cells acquire a stress response along the preoxygenation period, which makes them more resistant against the stressful conditions of the preoxygenation process and the subsequent fermentation.

Cell recycling during repeated very high gravity bio-ethanol fermentations using the industrial Saccharomyces cerevisiae strain PE-2

“…The common practice is aeration of the wort before pitching (strategy that we also performed in this work) thereby providing O 2 for lipid synthesis during the first stages of the fermentation (Ohno and Takahashi 1986). Another process engineering strategies to maximize the performance of yeast cells during consecutive batch fermentations include the oxygenation (aeration) of cropped yeast slurries (Verbelen et al 2009b), the addition of the required lipids to wort (Casey et al 1983) and the supplementation of cropped cells with unsaturated fatty acids (sometimes suggested as an alternative to aeration) (Moonjai et al 2002).…”

Stress responses in brewing yeast.

“…Transcription factors involved in oxygen sensing were found to be mainly increased in the first 3 h [43]. The initial stages of lager fermentation were also found to involve a rapid accumulation of ergosterol, which is an important factor in restoring the fermentation capacity of the cells after storage [44].…”

“…provzdušněním kvasinek před fermentací, navozuje velmi rychle (během 45 minut) drastickou odpověď na oxidativní stres spolu s akumulací trehalosy. Hladina transkripčních faktorů, které se účastní detekce kyslíku, je zvýšená hlavně během prvních 3 hodin [43]. V počátečních fázích kvašení je také rychle akumulován ergosterol, který je důležitý při obnovení fermentační kapacity buněk po jejich skladování [44].…”

Biomarkers to evaluate the effects of temperature and methanol on recombinant Pichia pastoris

“…The expression level of proteins in P. pastoris depends critically on growth conditions (Solà et al , 2007), such as temperature, carbon source (Ni et al , 2008) and oxygen (Verbelen et al , 2009), which have been proven to be cell type-specific and varied depending on the product that is generated, so it has not yet been achieved a specific method, like biomarkers, to determine the effects of these conditions to find the optimal parameters for each model. Among the adverse consequences caused by disregard the effects of these parameters on the cultivation of yeast, temperature conditions would affect the expression of the transcription factor known as factor of response to heat stress (HSF-1) (Gasser et al , 2007), so it would regulate HSP-70 expression.…”