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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The result of sensory evaluation of sake showed that acetic acid imparted desirable acidity when the proportion of acetic acid to lactic acid was about 1/3, even if the concentration of acetic acid was 0.75 g/l. Glycerol balanced the acidity and brought about a harmony between sweetness and acidity in sake. A high-acetate producing sake yeast (MHA-3) was isolated from mutants having low NADH dehydrogenase (NDE) activity. MHA-3 produced 15 times more acetate and 5 times more lactate than the parental strain Kyokai no. 901 (K-901) in a small-scale sake brewing test using 10 kg of rice. In addition, the concentrations of glycerol in sake brewed with MHA-3 were approximately 1.5-fold higher than in that brewed with K-901. The proportion of acetic acid to lactic acid was about 1/3 in sake fermented with MHA-3 and it exhibited a good balance between sweetness and acidity. The activities of glycerol-3-phosphate dehydrogenase (GPD) and aldehyde dehydrogenase (ALD) in MHA-3 were 1.4-fold and 3.1-fold, respectively, higher than those in K-901 while the activity of NDE was 40% that of K-901. MHA-3 accumulated higher amounts of acetate and glycerol than K-901 in static YNB10 medium. The concentrations of acetic acid produced, depending on the quantity of yeast cells added, increased in conjunction with increases in glycerol produced. We suggest that NDE might be linked with GPD and that the nde mutants, which can be used in sake brewing, produced higher amounts of acetate and glycerol.
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PMID:Isolation and characterization of a high-acetate-producing sake yeast Saccharomyces cerevisiae. 1623 68

Previous studies reported that the use of Metschnikowia pulcherrima in sequential culture fermentation with Saccharomyces cerevisiae mainly induced a reduction of volatile acidity in wine. The impact of the presence of this yeast on the metabolic pathway involved in pyruvate dehydrogenase (PDH) bypass and glycerol production in S. cerevisiae has never been investigated. In this work, we compared acetic acid and glycerol production kinetics between pure S. cerevisiae culture and its sequential culture with M. pulcherrima during alcoholic fermentation. In parallel, the expression levels of the principal genes involved in PDH bypass and glyceropyruvic fermentation in S. cerevisiae were investigated. A sequential culture of M. pulcherrima/S. cerevisiae at an inoculation ratio of 10:1 produced 40% less acetic acid than pure S. cerevisiae culture and led to the enhancement of glycerol content (12% higher). High expression levels of pyruvate decarboxylase PDC1 and PDC5, acetaldehyde dehydrogenase ALD6, alcohol dehydrogenase ADH1 and glycerol-3-phosphate dehydrogenase PDC1 genes during the first 3 days of fermentation in sequential culture conditions are highlighted. Despite the complexity of correlating gene expression levels to acetic acid formation kinetics, we demonstrate that the acetic acid production pathway is altered by sequential culture conditions. Moreover, we show for the first time that the entire acetic acid and glycerol metabolic pathway can be modulated in S. cerevisiae by the presence of M. pulcherrima at the beginning of fermentation.
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PMID:Metschnikowia pulcherrima Influences the Expression of Genes Involved in PDH Bypass and Glyceropyruvic Fermentation in Saccharomyces cerevisiae. 2870 1