Stable expression of glucoamylase gene in industrial strain of Saccharomyces pastorianus with less d diacetyl produced

Abstract

An integrating plasmid pMGI6 carrying glucoamylase gene (GLA) and using the yeast α-acetolactate synthase gene (ILV2) as the recombination sequence, was constructed from pBluescript II SK-. The ilv2::GLA fragment released from pMGI6 was introduced into the brewing yeast Saccharomyces pastorianus and the resulting recombinant strain was able to utilise starch as the sole carbon source, its glucoamylase activity was 6.3 U ml-1 and its a-acetolactate synthase activity was lowered by 33%. Fermentation tests confirmed that the diacetyl concentration in wort fermented by the recombinant strain was reduced by 66% and the maturation time was reduced from 7 to 4 days. The beer fermented by the recombinant strain under industrial operating conditions satisfied the high quality demands and the strain could be used in beer production safely.