A study to optimise the fermentation and production of Parāroa Rēwena: a traditional Māori bread : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy, School of Food and Advanced Technology, Massey University, Auckland, New Zealand. EMBARGOED to 12 January 2027.

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Massey University
Embargoed to 12 January 2027
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Parāroa Rēwena is a traditional Māori sourdough bread produced by fermentation using a potato starter culture (PSC). Rēwena sourdough bread is mainly produced at a household level among Māori communities in New Zealand using back-slopping. The PSC used in this study that was provided by Māori Kai Cuisine Ltd (Tauranga, New Zealand) is one particular source of the PSC among the Māori communities. While there could potentially be other sources of the PSC, this is the first study to understand the complexity and diversity of the PSC involved during the natural fermentation process of Parāroa Rēwena. The PSC used is likely to have evolved during the natural fermentation processes, therefore, its composition is undefined. The application of specific cultures and downstream sourdough fermentation impacts on bread texture, acidity, sensory profile, and the overall quality of sourdough bread. In addition, the metabolism of the fermenting microorganisms can potentially reduce levels of fermented oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) in the sourdough bread. Consumption of low FODMAPs foods can alleviate the symptoms of abdominal pain and bloating associated with irritable bowel syndrome (IBS). The production of consistent, high-quality products is more difficult without application of controlled fermentation. Further, to upscale the production of Rēwena sourdough bread, a thorough understanding of microbial metabolism, and the impact of fermentation parameters is necessary. Available data indicate that the PSC has not been characterised, therefore, there is scanty information on the culture. The current study investigated the composition of the PSC by characterising the growth, and carbohydrate metabolism of the fermenting microorganisms. The fermentation kinetics and the effect of fermentation temperatures and pH on the growth kinetics of the microorganisms from the PSC were also studied. The propagation conditions of the PSC were evaluated to determine the best parameters for the growth of the cultures, for the subsequent production of Rēwena sourdough bread. Sugars (maltose, glucose, fructose), organic acids (acetic acid, lactic acid), and FODMAPs (total fructan) were determined during the optimisation of fermentation of sourdough and the production of Rēwena sourdough bread.--Shortened abstract.
Lactobacillus, yeast, kinetic modelling, kinetic parameters, response surface methodology, total fructan content, FODMAPs, starter culture, sourdough bread