Browsing by Author "Wang, Boying"

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    Characteristics of dominant acetic acid bacteria and yeast in kombucha sold in New Zealand : a thesis submitted in partial fulfilment of the requirement for the degree of Master of Food Technology at Massey University, Auckland, New Zealand
    (Massey University, 2020) Wang, Boying
    Kombucha is a sparkling sugared tea beverage fermented with a symbiotic culture of acetic acid bacteria (AAB) and yeast. Despite the increase in the demand of the beverage due to its perceived health benefits and naturalness, its microbial composition, presumed to be probiotic is unknown at consumption. The microbial composition of the cultures are therefore important to processors and consumers. This study characterised the predominant AAB and yeasts present in Kombucha sold in New Zealand. AAB and yeasts were isolated from six Kombucha samples using glucose yeast extract peptone mannitol (GYPM) and yeast extract glucose chloramphenicol (YGC) media, respectively. The phenotypic identification of AAB and yeast was achieved by morphological and biochemical characterisations. The biochemical analysis of AAB included the oxidation of ethanol, ketogenesis of glycerol, oxidation of lactate and acid produced from different carbohydrates. Yeasts were identified using the API 32C kit and molecular sequencing of 23S rRNA whereas the AAB were identified using the 16S rRNA sequencing. The pH of the Kombucha samples ranged between 3.21 and 3.90 and the titratable acidity (TA) varied from 0.38-0.43%. The total soluble solids (TSS) ranged from 1.87 to 7.00 ºBrix. The microorganisms were only found in domestic Kombucha samples and not in the imported samples. Mean AAB counts ranged from 4.97±0.06 to 5.63±0.02 log CFU/mL, while yeast counts ranged from 4.75±0.10 to 5.69±0.01 log CFU/mL. Dominant AAB species were identified as Gluconobacter oxydans and Acetobacter musti, and the yeasts were Dekkera bruxellensis, Schizosaccharomyces pombes, Hanseniaspora valbyensis, Brettanomyces anamalus, Pichia kudriavzevii and Saccharomyces cerevisiae in the analysed Kombucha samples sold in New Zealand. The yeast community was more complex and variable than AAB community in the analysed Kombucha samples.
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    Characteristisation of acetic acid bacteria and yeast isolated from kombucha produced in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Auckland, New Zealand. EMBARGOED until 21 August 2026.
    (Massey University, 2024-08-13) Wang, Boying
    Background: Kombucha is a popular functional tea beverage commonly fermented by a complex symbiotic culture of acetic acid bacteria (AAB) and yeast (SCOBY) in a base of sugared tea infusion at ambient temperature for 7-14 days. Regular consumption of Kombucha confers potential health benefits due to the presence of live cultures and high concentrations of bioactive components such as vitamins, polyphenols, and organic acids. However, industrial production of Kombucha faces challenges due to the limited information on the dynamic changes in its microbial community composition and the lack of knowledge regarding their health-promoting characteristics. The impact of fermentation conditions and added substrates on starter cultures, physicochemical characteristics and functional activities is also not well understood. Objectives: This study aimed to determine the microbiological characteristics of New Zealand Kombucha starter cultures and evaluate the probiotic potential of AAB and yeast isolated from commercial Kombucha products. The bioactive components, antioxidant activity, and antimicrobial activities of Kombucha fermented using a New Zealand starter culture under different fermentation conditions were also determined.--Shortened abstract