Technical Session 16: Yeast III Session
Hiroshi Kitagaki, National Saga University
ABSTRACT: Residual pyruvate and acetolactate during
alcoholic fermentation leads to synthesis of off-flavor diacetyl.
Therefore, suppression of these substances during alcoholic fermentation
is desirable. In order to circumvent this problem, we came up with the
idea of modifying the mitochondrial transportation system, fortifying
the transportation of pyruvate from the cytosol to the mitochondria, and
decreasing the amount of pyruvate and acetolactate. To accomplish this,
we isolated mutants of sake yeast resistant to ethyl alpha-trans-cyanocinnamate, an inhibitor of mitochondrial pyruvate transport. The brewery yeast of sake,
the Japanese traditional rice wine, was used as the parent strain. This
strain indeed exhibited a decreased amount of pyruvate and acetolactate
during sake brewing on a factory scale. This was the first
success of development of a brewery yeast that produces a decreased
amount of pyruvate and acetolactate without deteriorated fermentation
ability. However, although we supposed that pyruvate transportation from
the cytosol to the mitochondria during alcoholic fermentation lowered
the pyruvate content, its mechanism had not been elucidated. Therefore,
we constructed sake yeasts that overexpress various mitochondrial transporters and investigated the resistance of the strains to ethyl alpha-trans-cyanocinnamate. As a result, the strain overexpressing the mitochondrial ATP/ADP translocator gene AAC1, exhibited resistance to ethyl alpha-trans-cyanocinnamate. This strain also exhibited a low pyruvate-producing ability during sake
brewing. These results suggest that transportation of ATP from the
cytosol to the mitochondria enhances pyruvate turnover within
mitochondria during alcoholic fermentation. It can also be inferred that
since an electron transport system using molecular oxygen does not
occur during alcoholic fermentation, ATP within mitochondria is
depleted, and mitochondria need to import ATP from the cytosol, where
ATP is synthesize through glycolysis. This research is the first to
propose a role of ATP transport from the cytosol to the mitochondria to
modify fermentation characteristics and suggest a novel strategy for
developing brewery yeasts that produce decreased amounts of pyruvate and
acetolactate.
Hiroshi Kitagaki received a Ph.D. degree from
the University of Tokyo. He began employment as a brewing analyst at the
National Taxation Bureau in 1995. He moved to the National Research
Institute of Brewing as a researcher in 2001. He worked as a visiting
researcher at the Medical University of South Carolina from 2005 to
2006. He is now an associate professor at the National Saga University.
He is the president of the Symbiotic Microbial Fermentation Engineering
Forum and has been selected as an associate member of the Science
Council of Japan and a program officer of the Ministry of Education,
Culture, Sports, Science and Technology, Japan. He has received the
Young Scientists’ Award in the Commendation of Science and Technology
from the Minister of Education, Culture, Sports, Science and Technology,
Japan; The Foundation of Agricultural Sciences of Japan; and The
Society for Biotechnology, Japan.
VIEW PRESENTATION 57