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Biotechnol Lett (2014) 36:16931699 DOI 10.1007/s10529-014-1530-5
ORIGINAL RESEARCH PAPER
Construction of dextrin and isomaltose-assimilating brewers yeasts for production of low-carbohydrate beer
Jin-Yeong Park Ja-Yeon Lee
Seung-Hyun Choi Hyun-Mi Ko Il-Chul Kim
Hwanghee Blaise Lee Suk Bai
Received: 25 February 2014 / Accepted: 1 April 2014 / Published online: 16 April 2014 Springer Science+Business Media Dordrecht 2014
Abstract Most Saccharomyces spp. cannot degrade or ferment dextrin, which is the second most abundant carbohydrate in wort for commercial beer production. Dextrin-degrading brewers bottom and top yeasts expressing the glucoamylase gene (GAM1) from Debaryomyces occidentalis were developed to produce low-carbohydrate (calorie) beers. GAM1 was constitutively expressed in brewers yeasts using a rDNA-integration system that contained yeast CUP1 gene coding for copper resistance as a selective marker. The recombinants secreted active glucoamylase, displaying both a-1,4- and a-1,6-debranching activities, that degraded dextrin and isomaltose and consequently grew using them as sole carbon source. One of the recombinant strains expressing GAM1 hydrolyzed 96 % of 2 % (w/v) dextrin and 98 % of 2 % (w/v) isomaltose within 5 days of growth. Growth, substrate assimilation, and enzyme activity of these strains were characterized.
Keywords Brewers yeasts Dextrin and
isomaltose assimilation Glucoamylase
Low-carbohydrate beer Saccharomyces
cerevisiae
Introduction
Dextrin, which is the main non-fermentable sugar during beer fermentation, comprises 2025 % of total wort carbohydrates. A reduction in wort dextrin content is a prerequisite to producing low-carbohydrate beers. Large amounts of exogenous enzymes that hydrolyze dextrin are added prior to fermentation to liberate fermentable sugars from wort dextrin during conventional beer fermentation (Hansen et al. 1990; Wang et al. 2010a, b). Alternative techniques to produce beer with decreased dextrin could be established by providing breweries with genetically-modied yeast strains that express amylolytic enzymes. The a-amylase gene (ALP1) from Saccharomycopsis buligera, the dextranase gene (LSD1) from Lipomyces starkeyi and the glucoamylase genes (STA, SGA1, and GLA) from Saccharomyces diastaticus, S. cerevisiae, and S. buligera have been used to develop brewers yeasts to reduce the caloric content of beer. However, these recombinant yeasts cannot completely degrade wort dextrins to fermentable sugars (Hansen et al. 1990; Liu et al. 2004, 2008; Wang et al. 2010a, b).
J.-Y. Park J.-Y. Lee S.-H. Choi I.-C. Kim
H. B. Lee S. Bai (&)
Department of Biological Sciences, College of...