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Rivista di Biologia Molecolare e Biotecnologie

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

lingua: Inglese

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.

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