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Subject: search.filters.subject.Malic acid

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    Maloethanolic deacidification of high acid juices during wine yeast alcoholic fermentation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University
    (Massey University, 1996) Ryan, Frances Alison
    Malic acid is a major acid found in grapes. In countries with cooler climates, such as New Zealand, this acid is not fully respired from grapes and will impart a sour taste on grape juices. Therefore steps must be taken to ensure deacidification of the juice or wine occurs. Deacidification is the process whereby the acidity of a juice or wine is lowered by physical, chemical or biological means. Biological methods of deacidification such as malolactic fermentation and maloethanolic fermentation involve the degradation of malic acid to other products. Malolactic fermentation is the bacterial conversion of malic acid to lactic acid and carbon dioxide and is commonly used in New Zealand wineries. Maloethanolic fermentation is the simultaneous conversion of grape sugars and malic acid to ethanol by specialized yeast strains and is the focus of this investigation. This research examines several commercially available yeast strains (Lallemand Lalvin strains 71B, ACID-, D432 and reference strains EC1118 and Red Star Montrachet (M)) and Schizosaccharomyces strain 442, for their ability to degrade malic acid during grape juice fermentation under New Zealand conditions. A Simulated Grape Juice medium was used to mimic these conditions, as well as commercial Chardonnay and Sauvignon Blanc juices. Strains 71B and D432 consistently degraded the greatest percentage of malic acid under all conditions and parameters investigated in this research. Respectively, these strains degraded malic acid by 36% and 22% of the initial concentration (7.0g/L) in industrial Chardonnay juice fermentations and by 47% and 36% of the initial concentration (3.7g/L) in industrial Sauvignon Blanc fermentations. Furthermore, in Sauvignon Blanc wines, a significant (P=0.05) difference was found between the wine made with strain 71B and all other wines. However, in Chardonnay wines, a significant difference was found between the wine made with strain D432 and all other wines. In addition, molecular genetic techniques (CHEF chromosomal banding pattern polymorphisms) were utilised to confirm yeast strain identity. from industrial fermentations. From this, it was concluded that all strains inoculated into the commercial juices were dominant at the most vigorous stage of fermentation. Factors influencing malic acid degradation were investigated in Simulated Grape Juice fermentations. These included initial concentrations of malic acid and nitrogen and the initial pH level of the juice. It was found that strains 71B and D432 degraded the greatest percentage of malic acid when the initial malic acid concentration of the juice was high (7.5g/L), the initial nitrogen concentration was low (463mg/L with proline) and an initial pH of pH 3.5. These results indicate that there is an interaction between yeast and grape variety/maturity, and that proper selection of yeast strain can be used as a tool for deacidification.
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    Investigations on malic acid utilisation in Schizosaccharomyces species : a thesis presented in partial fulfilment of the requirements for the degree in Doctor of Philosophy in Genetics at Massey University
    (Massey University, 1990) Cambourn-Theewis, Wilhelmina Margaretha
    The aims of this investigation were: to determine whether alterations in uptake, or metabolism, of glucose and malate was the cause of malate dependence; to determine the number of genes involved in malate dependence; and to clone the gene(s) involved. A malate dependent mutant, i.e. a mutant that requires both malate and glucose for growth, (mutant 11) of Schizosaccharomyces malidevorans 442 was characterised. Malic enzyme activity was increased almost ten-fold. The Vmax of malate uptake was increased four-fold compared to S. malidevorans 442. Uptake of glucose was significantly lower in mutant 11 than the wild-type. The kinetics of glucose uptake by S. malidevorans 442 and mutant 11 suggested the presence of two glucose transporters, a high affinity and a low affinity transporter. Only the low affinity transport was apparently altered in mutant 11 compared to the wild-type. Genetic analysis indicated that the malate dependent mutation is recessive and is the result of a single mutational event. Crosses involving derivatives of mutant 11 and Schizosaccharomyces pombe strains did not yield the expected segregation of markers. Tetrad analysis showed that the spore viability was very low. It was not possible, therefore, to determine linkage of the malate dependence locus and any other loci. All malate dependent strains were apparently homothallic although linkage between the mating-type locus and malate dependence could not be established. The isolation of similar mutants from homothallic strains of S. pombe, but not from heterothallic strains, provided strong support for the requirement of homothallism for malate dependence. The pulse field gel electophoresis karyotypes of mutant 11 and derivatives of mutant 11 suggested the presence of a large chromosomal rearrangement of chromosome 2 that cosegregated with malate dependence. Malate dependent mutants were not obtained from homothallic Saccharomyces cerevisiae MD26. A malate dependent mutant (WT 6) was isolated from S. pombe WT 4 and found to have characteristics similar but not identical to those of mutant 11. WT 6 demonstrated increased utilisation of malate and decreased utilisation of glucose. Malic enzyme activity was not altered in WT 6 compared to the wild-type. Malate uptake was not affected. The karyotype of WT 6 suggested that a chromosomal rearrangement had occurred, but it is not identical to the rearrangement in mutant 11. The differences in the characteristics of mutant 11 and WT 6 suggested the mutations in these mutants may not be identical. The finding that mutant 11 and WT 6 belong to different complementation groups could explain these differences. Although differences were found in the uptake of malate and glucose, the inability of malate dependent mutants to grow on glucose implicates a defect in glucose metabolism.