Fermentation Characteristics of Brewing Yeast HCS with Glucoamylase Expression by Rare Mating and Beer Analysis

Among the yeast strain development methods, rare mating was used to select respiratory deficient (RD) mutants from Saccharomyces cerevisiae HBC52 strain. Glucoamylase gene of Saccharomyces diastaticus kl14 was induced into the RD mutant. RD mutant strain that could uptake maximum amount of non-fermentable sugars through the expression of glucoamylase gene was developed and the fermentation characteristics of developed strain were investigated. The possibilities of Saccharomyces cerevisiae HCS strain as a brewing yeast are as follows. In the final sugar analysis of beer, HBC52 showed sugars from glucose to degree of polymerization (DP) 6, but HCS showed sugars mostly from glucose to DP 4. After fermentation, the pH of HBC52 and HCS were 3.98 and 4.18-4.22, respectively. During fermentation process, maximum suspension yeast cell numbers of HBC52 and HCS were $74{\times}10^6 \;cells/mL\;and\;$74-77{\times}10^6\;cells/mL.$ Cell propagation of HCS strains were slower than brewing yeast. The amount of suspended HCS cells was larger than HBC52 after fermentation. In comparative experiment of flavour compounds fermented and young beer, acetaldehyde content was higher in HCS strain than in HBC52 strain. Esters were increased in HBC52 and HCS3 during storage while the number of HCS1 and HCS2 cells decreased. Utilization of HCS strain in the production of low carbohydrate beer could greatly reduce economic cost by not using commercial enzymes in mashing process.