Publications (1)0 Total impact
ABSTRACT: J. Inst. Brew. 114(4), 322–328, 2008 The secretion of proteinase A (encoded by PEP4) from brewer's yeast is detrimental to the foam stability of unpasteurized beer. The aim of this study was to construct mutants of the allopoly-ploid Saccharomyces carlsbergensis strain TT, which were par-tially or completely deficient in proteinase A activity. Allelic PEP4 genes were consecutively disrupted by using the Cre-loxP recombination system combined with PCR-mediated gene dis-ruption. A single PEP4 deletion mutant TT-M was successfully constructed. However, no viable mutant could be obtained when the second allelic PEP4 gene was deleted. The brewing perfor-mances of the parent strain and the modified strain were com-pared on a 100 L pilot fermenter scale. Proteinase A activity in fermented wort brewed with mutant strain TT-M was signifi-cantly lower (p<0.05) than that of the parent strain TT, whereas no significant difference on either maltose or maltotriose assimi-lation (p>0.05) was found. The mutant TT-M remained geneti-cally stable, as shown by diagnostic PCR, after re-streaking for 20 generations. The flavor and taste of the final fermented wort, brewed with the mutant strain TT-M, was evaluated by the Tsingtao expert sensory panel, and found to be comparable to that of the parent strain and exhibited no distinct defects. The flavor component profiles of these two finished products were also comparable. The study demonstrated allelic genes in poly-ploid industrial yeasts could be efficiently and consecutively deleted by the retractive primer disruption strategy, and the mu-tant of Saccharomyces carlsbergensis partially deficient in pro-teinase A contributed to an improvement in foam stability.