Physiology of Free and Immobilised Brewer’s Yeast in Stress Conditions
An increase in substrate concentration in ethanol fermentation results in higher metabolic activity and increased ethanol production; however, during fermentation of concentrated substrates, the yeasts are exposed to extreme conditions and show differences in metabolism accompanied with many negative consequences. A significant increase of fermentation rate of VHG wort for entrapped yeasts in contrast to free yeast cells was observed. The specific rate of ethanol production of yeast immobilised in calcium pectate in wort of concentration 24 % (w/w) was at the level of the specific rate of ethanol production of free yeast and yeast adsorbed on cellulose in wort of concentration 16 %. An increase in wort gravity resulted in significantly higher trehalose content in free cells, whereas trehalose content in entrapped cells did not increase with increasing initial wort gravity up to the concentration of 24 %. Higher degree of saturation of total fatty acids in the entrapped fermenting yeast compared to the free cells under VHG fermentation conditions correlated positively with ethanol tolerance and improved fermentation rate. Beer produced from VHG wort by entrapped yeasts had a suitable diacetyl concentration and higher alcohols-to-esters ratio, as opposed to beer produced by free yeasts.
KeywordsEthanol Production Calcium Alginate Ethanol Tolerance Unsaturation Index Trehalose Content
This work was supported by the Scientific Grant Agency of the Ministry of Education of the Slovak Republic and the Academy of Sciences, registration number 1/0096/11.
- Polednikova M, Voborsky J, Chladek L, Sruma T (1993) Zkusenosti svyrobou piva pomoci imobilizovanych kvasinek. Kvas Prumysl 39:2–7Google Scholar
- Smogrovicova D, Patkova J, Domeny Z, Navratil M (2000) Improvement in beer fermentation under very high gravity conditions by entrapped yeast. Minerva Biotechnol 12:331–336Google Scholar
- Smogrovicova D, Domeny Z, Navratil M, Dvorak P (2001) Continuous beer fermentation using polyvinyl alcohol entrapped yeast. In: Proceedings of European brewery convention, 28th congress, Budapest, pp 477–485Google Scholar