Browsing by Author "Botma, Izak Johannes"

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    Lactobacillus plantarum : amino acid utilization
    (Stellenbosch : Stellenbosch University, 2018-03) Botma, Izak Johannes; Du Toit, Maret; Bauer, Florian; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
    ENGLISH ABSTRACT: Amino acid metabolism serves as a source of sulphur, carbon and nitrogen for bacteria growing in wine or grape juice. The metabolism of amino acids controls the rate of growth and malic acid degradation and also results in the formation of various aromatic compounds which may positively or negatively influence the aroma profile of wine. L. plantarum, a lactic acid bacterium (LAB), may be used as co-inoculant in high pH (≥ 3.5) grape juice for fast malic acid degradation and high aroma production. Since the research on L. plantarum nitrogen metabolism is scarce, the overall goal of this study was to better understand it. The first aim was to determine the amino acid requirements in L. plantarum for growth and malic acid degradation, through single amino acid omissions. This entailed inoculation of nitrogen starved L. plantarum strains into chemically defined media (in this case synthetic grape juice) in which one amino acid is removed at a time. The data suggests that amino acid trophic requirements in L. plantarum are highly strain dependent, although Leu, Ile, Val, Glu and Met were shown under our conditions to be essential amino acids and Gln, Gly, His, Lys and Trp were non-essential amino acids. In a subsequent experiment, 5 single amino acid omissions (Ala, Arg, Gln, Trp and Val) were selected to evaluate their effect on growth and malic acid uptake in synthetic grape juice. During malolactic fermentation (MLF) the removal of Ala and Val had completely repressed MLF induced by L. plantarum while the removal of Trp and Arg had somewhat repressed MLF. Only the removal Gln did not hinder MLF for at least one strain. The second aim was to determine the order of amino acid uptake by L. plantarum in synthetic grape juice using HPLC. Asp, Thr, Ser and Ala tends to be assimilated at a high rate within the first 72 h while the branched chain amino acids, aromatic amino acids (AAA) and Met are assimilated after 72 h. The third aim determined the amino acid uptake in Chardonnay grape juice. The assimilation pattern differed considerably between synthetic grape juice and Chardonnay grape juice. In contrast to synthetic grape juice Arg, Leu, Phe and Ala were preferred amino acid sources. It is thought that the differences could be attributed to mainly two factors: initial nitrogen concentration (40 mg N/L in SGJ vs 240 mg N/L in grape juice) and the pre-culture conditions. This study confirmed that higher nitrogen concentrations resulted in higher growth and quicker malic acid degradation. The high nitrogen requirement of certain amino acids combined with the harsh wine parameters experienced in sequential MLF might explain why L. plantarum struggles with MLF in this scenario. Further research should be directed towards identifying the preferred amino acids in dried and fresh L. plantarum starter cultures to assess if there is a difference. If nitrogen requirements continues to be investigated in L. plantarum successful tailored supplements can be created to aid the growth of L. plantarum in wine or grape juice.