The Role of Magnesium and Calcium in Governing Yeast Agglomeration

Rosslyn M. Birch³, Ann Dumont² and Graeme M. Walker¹*

¹Division of Molecular and Life Sciences, School of Contemporary Sciences, University of Abertay Dundee, Kydd Building, Bell Street, Dundee DD1 1HG, Scotland, UK
²Lallemand Inc., Research & Development, 6100 Royalmount Avenue, Montreal, Quebec, H4P 2R2, Canada
³Current Address: Department of Molecular and Cell Biology, Institute of Medical Sciences, University of Aberdeen, Forresterhill, Aberdeen AB25 2ZD, Scotland, UK

Article history:
Received: December 17, 2001
Accepted: June 18, 2002

Key words:
yeast, agglomeration, metal ions

Summary:
»Grit« formation by agglomerating cells of baker’s yeast is an idiosyncratic phenomenon of irreversible cellular aggregation that is detrimental to yeast quality. Agglomeration results in failure of rehydrated dried yeast to evenly resuspend and has economic consequences for both yeast manufacturers and bakers. Several environmental factors are implicated in governing yeast agglomeration, but no significant differences between 'gritty' and 'non-gritty' yeast in terms of cell hydrophobicity or flocculence have been reported. In this study, analysis of cellular metal ions has revealed high levels of calcium in 'gritty' strains of Saccharomyces cerevisiae, which suggests that calcium ions may positively influence agglomeration. In contrast, it was found that cellular magnesium levels were higher in 'non-gritty' yeast. Furthermore, by increasing magnesium concentrations in molasses yeast growth media, a reduction in cellular calcium was observed and this concomitantly reduced the tendency of cells to agglomerate and form grit. Magnesium thus acted antagonistically against calcium-induced agglomeration, possibly by blocking calcium binding to yeast cell surface receptors. Results suggested that yeast agglomeration and metal ion bioavailability were inextricably linked and the findings are discussed in relation to possible measures of alleviating cellular agglomeration in the production of baker’s yeast. 

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