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Minerva Biotecnologica 2000 December;12(4):331-5

Copyright © 2000 EDIZIONI MINERVA MEDICA

language: English

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


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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.

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