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

Abstract

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.