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Rivista di Biologia Molecolare e Biotecnologie
Indexed/Abstracted in: EMBASE, Science Citation Index Expanded (SciSearch), Scopus
Impact Factor 0,246
Minerva Biotecnologica 2000 Dicembre;12(4):331-5
Improvement in beer fermentation under very high gravity conditions by entrapped yeast
Smogrovicova D., Patkrova J., Domény Z., Navratil M.
Department of Biochemical Technology, Faculty of Chemical Technology, Slovak University of Technology, Bratislava, Slovak Republic
Background. This study is concentrated on an improvement of beer fermentation under very high gravity (VHG) conditions using immobilised bottom-fermenting yeast strain Saccharomyces cerevisiae.
Methods. The yeast cells, free or immobilised in calcium alginate, calcium pectate, k-carrageenan, agar or DEAE-cellulose, were used for batch wort fermentation of different gravity - 12 to 30% (w/w). A significant increase of fermentation rate of VHG wort for yeasts entrapped in calcium pectate or calcium alginate in comparison to free cells was observed.
Results. The specific rates of saccharides utilisation and ethanol production of free yeasts and yeasts immobilised on DEAE-cellulose were very similar at all concentrations of wort and were reduced, as compared to yeasts immobilised in other carriers studied. Ethanol toxicity affects mainly the cell membrane by altering the lipid bilayer and thus weakening the structure. The yeast responds by increasing its intracellular contents as well as the unsaturated fatty acid concentration. Increasing concentration of produced ethanol decreased the relative percentage of saturated fatty acids, especially palmitic (16:0) and stearic (18:0), more in free and on DEAE-cellulose immobilised cells than in yeast immobilised by entrapment.
Conclusions. The results confirm that immobilisation protects the microbial cells against the possible toxic effect of substrates or products whereby entrapment in gel appeared to be more favourable than adsorption. If the gel matrix contained calcium cations, the ethanol tole-rance was even more improved.