Reference: Vidgren V, et al. (2009) Improved fermentation performance of a lager yeast after repair of its AGT1 maltose and maltotriose transporter genes. Appl Environ Microbiol 75(8):2333-45

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Abstract

The use of more concentrated, so-called high gravity and very high gravity (VHG) brewer's worts for the manufacture of beer has economic and environmental advantages. However, many current strains of brewer's yeasts ferment VHG worts slowly and incompletely, leaving undesirably large amounts of maltose and, especially, maltotriose in the final beers. alpha-Glucosides are transported into Saccharomyces yeasts by several transporters, including Agt1, which is a good carrier of both maltose and maltotriose. The AGT1 genes of brewer's ale strains encode functional transporters, but the AGT1 genes of studied lager strains contain a premature stop codon and do not encode functional transporters. In the present work, one or more copies of the AGT1 gene of a lager strain were repaired, by using DNA sequence from an ale strain, and put under the control of a constitutive promoter. Compared to the untransformed strain, the transformants with repaired AGT1 had higher maltose transport activity, especially after growth on glucose (which represses endogenous alpha-glucoside transporter genes), and higher ratios of maltotriose transport activity to maltose transport activity. They fermented VHG (24 degrees P) wort faster and more completely, producing beers containing more ethanol and less residual maltose and maltotriose. The growth and sedimentation behaviours of the transformants were similar to those of the untransformed strain, as were the profiles of yeast-derived volatile aroma compounds in the beers.

Reference Type
Journal Article
Authors
Vidgren V, Huuskonen A, Virtanen H, Ruohonen L, Londesborough J
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