Exploring the potential of non-conventional yeasts in the production of unique flavour profiles for the beverage industry

Abstract

The interest in non-conventional yeasts (NCY) has grown exponentially in the last decade, mainly for their potential application in the beverage industry due to their unique metabolic traits and capacity to produce novel beverages with distinct flavour profiles. Yet, the practical application of these yeasts in industrial settings is still in early development, with only a few strains commercially available. This is mainly caused by the dominance of Saccharomyces cerevisiae in the beverage industrial processes, as well as a lack of sufficient knowledge regarding NCY. To tackle this and contribute to the commercial adoption of NCY, I have provided new tools and insights that will be of value to brewers and food scientists. First, I developed a new method that allows for the screening of vast conventional and non-conventional yeast libraries by using colony size as a proxy for fitness. I then utilised the method for assessing the suitability of several NCY to grow on wort and further measured their volatile aroma compound production. Due to the outstanding aroma compound production of Hanseniaspora vineae, I selected it for mixed wort co-fermentation together with an S. cerevisiae brewing strain utilizing different inoculum ratios. This yielded fermented wort with standard ethanol content and unique fruity flavour profiles, determined by the inoculum ratio. Furthermore, I studied a spontaneous traditional English cider fermentation by assessing the microbial population dynamics through metagenomics. With this, I confirmed previous evidence on the overall microbial successions reported in spontaneous fermentations of wine and cider, as well as highlighted a potential unknown key role of Malassezia sp., Cladosporium sp. and Tatumella sp. in the spontaneous fermentation of traditional English cider. Then, I isolated more than one hundred yeasts from the cider farm and the spontaneous fermentation and characterised their growth under cider-making conditions by employing our own recently developed high-throughput screening method. Lastly, I measured the aroma compound production of a subset of the isolates in apple juice fermentations, identifying the main aroma contributors to the spontaneous fermentation, as well as potential candidates for the development of wild NCY starters for cider production. Overall, the findings of this thesis contribute to the body of evidence that supports the potential of NCY for the production of unique beverages, as well as providing a new method for the screening of NCY and highlighting cider spontaneous fermentation as a valuable source of yeasts with potential applicability in the beverage industry.

Date of Award	12 Jul 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Daniela Delneri (Main Supervisor) & Raymond O'Keefe (Co Supervisor)