Abstract
A sparkling-type draft cloudy sake (Japanese rice wine), AWANAMA, was recently developed using high hydrostatic pressure (HHP) treatment as a non-thermal pasteurization method. This prototype sake has a high potential market value, since it retains the fresh taste and flavor similar to draft sake while avoiding over-fermentation. From an economic point of view, a lower pressure level for HHP pasteurization is still required. In this study, we carried out a genome analysis of a pressure-sensitive (piezosensitive) mutant strain, a924E1, which was generated by UV mutagenesis from a laboratory haploid Saccharomyces cerevisiae strain, KA31a. This mutant strain had a deletion of the COX1 gene region in the mitochondrial DNA and had deficient aerobic respiration and mitochondrial functions. A metabolomic analysis revealed restricted flux in the TCA cycle of the strain. The results enabled us to use aerobic respiration deficiency as an indicator for screening a piezosensitive mutant. Thus, we generated piezosensitive mutants from a Niigata-sake yeast strain, S9arg, which produces high levels of ethyl caproate but does not produce urea and is consequently suitable for brewing a high-quality sake. The resultant piezosensitive mutants showed brewing characteristics similar to the S9arg strain. This study provides a screening method for generating a piezosensitive yeast mutant as well as insight on a new way of applying HHP pasteurization.
Highlights
Faculty of Applied Life Sciences, Niigata University of Pharmacy and Applied Life Sciences, Graduate School of Applied Life Sciences, Niigata University of Pharmacy and Applied Life Sciences, Department of Applied Bioscience, College of Bioscience and Chemistry, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi 921-8501, Japan
Strain a924E1 showed a larger loss of viability than the parent strain when subjected to high hydrostatic pressure (HHP) treatment at 175 to 250 MPa at temperatures from 4 to 40 ◦ C [7], as well as when subjected to thermal treatment at 50 to 58 ◦ C under atmospheric pressure [2]. These results indicated that this mutant strain was sensitive to both HHP and thermal stresses
The Niigata-sake yeast S. cerevisiae strain S9arg used in this study was provided by the Niigata Prefectural Sake Research Institute (Niigata city, Niigata, Japan)
Summary
Yeast strains used were the wild-type haploid S. cerevisiae strain KA31a (MATa, his, leu, trp, and ura3) and its piezosensitive mutant strain a924E1 (MATa, his, leu, trp, and ura3) [1]. The Niigata-sake yeast S. cerevisiae strain S9arg used in this study was provided by the Niigata Prefectural Sake Research Institute (Niigata city, Niigata, Japan). The piezosensitive strains derived from strain S9arg, strain UV1, and NM1, were produced during this study. The strains were usually grown aerobically on a YPD medium (1% yeast extract, 2% peptone; Becton Dickinson and Co., Franklin Lakes, NJ, USA, and 2% glucose; FUJIFILM Wako Pure Chemical, Osaka, Japan) at 30 ◦ C for 48 h
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