X-F Liu1, Z-Y Wang, J-J Wang, Y Lu, X-P He, B-R Zhang. 1. The Laboratory of Molecular Genetics and Breeding of Yeast, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
Abstract
AIMS: Construction of an industrial brewer's yeast strain, which could improve foam stability and reduce calorific values of beer. METHODS AND RESULTS: An industrial brewer's yeast strain (Ts-10) was constructed by integrating glucoamylase encoding gene GAI amplified from Saccharomycopsis fibuligera by PCR into the locus of proteinase A (PrA) gene (PEP4). The resulting recombinant strain identified by PCR could grow on YNB minimal medium plate with starch as sole carbon source. Its highest GAI activity was 91.69 U ml(-1), but it had no PrA activity. The real extract was reduced by 21.07% and the main residual maltotriose content was reduced by 14% in wort fermented with the recombinants strain. Its foam retention in beer was higher 39 s and the contents of potential off-flavour compounds, such as diacetyl, pentanedione and acetaldehyde were lowered by 16%, 13% and 14%, respectively, as compared with the industrial brewer's yeast YSF-5. CONCLUSIONS: An industrial brewer's yeast strain was constructed by introducing GAI gene and disrupting PEP4 gene. SIGNIFICANCE AND IMPACT OF THE STUDY: The recombinant strain (Ts-10) had better foam performance and mouthfeel in addition to low-calories values. It was free of heterologous DNA sequences and drug-resistance genes and could be safely used in beer production.
AIMS: Construction of an industrial brewer's yeast strain, which could improve foam stability and reduce calorific values of beer. METHODS AND RESULTS: An industrial brewer's yeast strain (Ts-10) was constructed by integrating glucoamylase encoding gene GAI amplified from Saccharomycopsis fibuligera by PCR into the locus of proteinase A (PrA) gene (PEP4). The resulting recombinant strain identified by PCR could grow on YNB minimal medium plate with starch as sole carbon source. Its highest GAI activity was 91.69 U ml(-1), but it had no PrA activity. The real extract was reduced by 21.07% and the main residual maltotriose content was reduced by 14% in wort fermented with the recombinants strain. Its foam retention in beer was higher 39 s and the contents of potential off-flavour compounds, such as diacetyl, pentanedione and acetaldehyde were lowered by 16%, 13% and 14%, respectively, as compared with the industrial brewer's yeast YSF-5. CONCLUSIONS: An industrial brewer's yeast strain was constructed by introducing GAI gene and disrupting PEP4 gene. SIGNIFICANCE AND IMPACT OF THE STUDY: The recombinant strain (Ts-10) had better foam performance and mouthfeel in addition to low-calories values. It was free of heterologous DNA sequences and drug-resistance genes and could be safely used in beer production.