3 results for Anfang, Nicole

  • Wine yeasts of New Zealand: an investigation into their distribution, contribution to sauvignon blanc aroma and interaction in co-ferments

    Anfang, Nicole (2010)

    Doctoral thesis
    The University of Auckland Library

    Sauvignon Blanc is the most important grape variety for New Zealand’s economy with exports of ~$740M in 2008. The two varietal thiols 3‐mercaptohexanol (3MH) and 3‐mercaptohexyl acetate (3MHA), reminiscent of tropical aromas like passion fruit and grapefruit, have been identified as key aroma compounds in Marlborough Sauvignon Blanc. These compounds are released during fermentation due to the metabolic action of yeast. This thesis investigates the contribution of natural New Zealand yeast isolates to the characteristic aroma of Sauvignon Blanc. Natural Saccharomyces and non‐Saccharomyces isolates were screened for their 3MH and 3MHA production. Four non‐ Saccharomyces yeasts from two species, Candida zemplinina and Pichia kluyveri, were identified as predominantly producing either 3MH or 3MHA. In subsequent cofermentation experiments with commercial S. cerevisiae strains, the combination of VL3 and P. kluyveri I at a ratio of 1:9 showed remarkable increase in 3MHA production. Analysis of nitrogen usage in this co‐ferment revealed that P. kluyveri I was able to grow on proline as sole nitrogen source in a synthetic medium. Proline is one of the most abundant amino acids in grape juice but cannot be utilized by S. cerevisiae as its degradation pathway requires oxygen. Nothing is known about proline utilization in P. kluyveri but the data presented here suggests a different utilization pathway than that found in S. cerevisiae.

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  • A distinct population of Saccharmoyces cerevisiae in New Zealand: evidence for local dispersal by insects and human-aided global dispersal in oak barrels

    Goddard, Matthew; Anfang, Nicole; Tang, RongYing; Gardner, Richard; Jun, Chen (2010)

    Journal article
    The University of Auckland Library

    Humans have used S. cerevisiae to make alcoholic beverages for at least 5000 years and now this super-model research organism is central to advances in our biological understanding. Current models for S. cerevisiae suggest that its population comprises distinct domesticated and natural groups as well as mosaic strains, but we generally know little of the forces which shape its population structure. In order to test the roles that ecology and geography play in shaping the S. cerevisiae species we examined nine variable microsatellite loci in 172 strains of S. cerevisiae isolated from two spontaneous grape juice ferments, soil, flowers, apiaries and bark in New Zealand. Bayesian analysis shows that the S. cerevisiae in NZ comprise a subdivided but interbreeding population that out-crosses ∼20% of the time. Some strains contributing to spontaneous ferments cluster with NZ soil/bark isolates, but others cluster with isolates from French oak barrels. It seems some strains have been globally dispersed by humans in oak barrels while some are locally vectored by insects. These data suggest geography is more important than ecology in shaping S. cerevisiae's population structure.

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  • Co-fermentation with Pichia kluyveri increases varietal thiol concentration in Sauvignon blanc

    Anfang, Nicole; Brajkovich, M; Goddard, Matthew (2009)

    Journal article
    The University of Auckland Library

    Background and Aims:  Volatile varietal thiols are one class of yeast metabolite that add aroma/flavour to Sauvignon Blanc, particularly to the Marlborough style from New Zealand. While various strains of Saccharomyces cerevisiae are known to liberate such thiols, there are no data examining whether non-Saccharomyces species effect concentrations of these thiols in wine. Methods and Results:  We screened a variety of New Zealand wine yeast isolates and found some that were able to liberate either 3-mercaptohexan-1-ol (3MH) or 3-mercaptohexyl acetate (3MHA). We show that co-fermentation with specific commercial strains and an isolate of Pichia kluyveri from New Zealand, at a 1:9 starting ratio, significantly enhances the 3MHA concentrations in Sauvignon Blanc compared with single species ferments. Conclusions:  Co-fermentation with this isolate of P. kluyveri may provide a means to elevate 3MHA concentrations in Sauvignon Blanc; the mechanism behind this increase is unknown. Significance of the Study:  Techniques that allow the predictable manipulation of varietal thiols potentially provide tools for winemakers to alter wine style without the use of genetically modified organisms.

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