Copper Tolerance and Biosorption of Saccharomyces cerevisiae during Alcoholic Fermentation

Abstract

At high levels, copper in grape mash can inhibit yeast activity and cause stuck fermentations. Wine yeast has limited tolerance of copper and can reduce copper levels in wine during fermentation. This study aimed to understand copper tolerance of wine yeast and establish the mechanism by which yeast decreases copper in the must during fermentation. Three strains of Saccharomyces cerevisiae (lab selected strain BH8 and industrial strains AWRI R2 and Freddo) and a simple model fermentation system containing 0 to 1.50 mM Cu2+ were used. ICP-AES determined Cu ion concentration in the must decreasing differently by strains and initial copper levels during fermentation. Fermentation performance was heavily inhibited under copper stress, paralleled a decrease in viable cell numbers. Strain BH8 showed higher copper-tolerance than strain AWRI R2 and higher adsorption than Freddo. Yeast cell surface depression and intracellular structure deformation after copper treatment were observed by scanning electron microscopy and transmission electron microscopy; electronic differential system detected higher surface Cu and no intracellular Cu on 1.50 mM copper treated yeast cells. It is most probably that surface adsorption dominated the biosorption process of Cu2+ for strain BH8, with saturation being accomplished in 24 h. This study demonstrated that Saccharomyces cerevisiae strain BH8 has good tolerance and adsorption of Cu, and reduces Cu2+ concentrations during fermentation in simple model system mainly through surface adsorption. The results indicate that the strain selected from China’s stress-tolerant wine grape is copper tolerant and can reduce copper in must when fermenting in a copper rich simple model system, and provided information for studies on mechanisms of heavy metal stress.

Effect of copper stress on growth characteristics and fermentation properties of Saccharomyces cerevisiae and the pathway of copper adsorption during wine fermentation

“…The second was an industrial strain, AWRI R2 (A; Maurivin Co., Australia), commonly used by Chinese winemakers for its good fermentation performance. Strain B showed characteristics of copper resistance and a good copper adsorption capacity in our preliminary experiment (Sun et al, 2015b). The yeasts, maintained on slants, were pre-cultured aerobically to mid-log phase (OD 600 was approximately 1.4) in shaking flasks containing 60 ml YPD medium (1% yeast extract, 2% peptone, and 2% glucose) at 28°C, 120 r/m (Du et al, 2012).…”

“…Cell growth was quantified by measuring the OD 600 of the fermenting MSM with a UV1800 spectrophotometer (Shimadzu, Japan) (Liu et al, 2015;Sun et al, 2015b). MSM, free of Cu 2+ , was used as the blank control.…”

“…Living yeast adsorption can be further divided into extracellular and intracellular adsorption (Chen et al, 2014). There have been a number of reports on yeast biological adsorption of heavy metals, mainly focused on the factors which influence the heavy metal adsorption properties (Brady & Duncan, 1994;Vasudevan et al, 2002), dynamic models of adsorption (Vasudevan et al, 2003), adsorption mechanisms (Suh et al, 1998), the pretreatment and immobilisation of the biological adsorbent, the cell morphology and subcellular structure changes (Chen et al, 2014;Sun et al, 2015b), et al Most of these reports pertained to industrial wastewater treatment systems. Very few reports exist on wine fermentation systems, and the few papers have focused only on the adsorption rate and adsorption capacity (Ferreira et al, 2006;Vasudevan et al, 2003).…”

“…For this study, we chose one industrial S. cerevisiae strain (AWRI R2) and one laboratory S. cerevisiae strain (BH8) which showed both good copper resistance and copper adsorption capacity in our preliminary experiment (Sun et al, 2015b). We studied the growth activity and fermentation performance of these strains under a copper concentration of less than 20 mg/l copper to gain a better understanding of the effects of low concentrations of copper on S. cerevisiae and wine production.…”

Biosorption of heavy metal copper (Cu2+) by Saccharomyces cerevisiae

“…SEM produces high-resolution images of a sample surface, capturing a complete size of approximately 1 -5 nm and can produce 3-dimensional shape characteristics so as to provide easier data about the analysed samples [12]. Based on Figure 7 and Figure 8 we can see the difference in cell morphology before and after contact with Cu 2+ .…”