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Spoilage is a major problem for the food industry ultimately resulting in economic loss. Among the most prominent spoilage yeasts are members belonging to the Zygosaccharomyces genus. This research focuses on differences in organic acid resistance and the physiological basis of these differences between Zygosaccharomyces bailii, Zygosaccharomyces kombuchaensis and Saccharomyces cerevisiae. Z. bailii , Z kombuchaensis and S. cerevisiae differ in resistance to short, medium and longer chain organic acids. Organic acid resistance was shown to be effected by alterations to growth conditions. S. cerevisiae was the most sensitive to organic acids followed by Z. kombuchaensis. Z. bailii was overall the most resistant to organic acids. Organic acid inhibition was shown to increase with increasing chain length. Electron microscopy was used to determine the effects of organic acids on yeast cell structure. Evidence is presented for short, medium and longer chain organic acids differing in their mode of inhibition. The cell wall was highlighted as differing between Z. bailii, Z. kombuchaensis and S. cerevisiae and as having a role in yeast organic acid resistance. Protoplast fusion was successfully applied to Z. bailii and Z. kombuchaensis with S. cerevisiae to study the role of mitochondria in yeast organic acid resistance. Differences in sensitivity to ethidium bromide and petite forming capabilities were demonstrated. Hybrids were characterized in terms of morphology, physiology and organic acid resistance. The ability of Z. bailii, Z. kombuchaensis and S. cerevisiae to form pseudohyphae in the presence of isoamyl alcohol was assessed. Isoamyl alcohol was shown to induce an osmotic stress with a role for the high osmolality glycerol pathway being demonstrated. Z. bailii was shown to contain a subgroup based on differences in organic acid resistance, morphology, physiology and molecular composition. This is the first time that a subgroup with increased sensitivity to organic acids has been reported for Z. bailii.

As controversies between studies have arisen over the properties and characteristics of the xanthan for the last decades, the current work aimed to establish the role of the xanthan molecular fine structure on its rheological and thermal properties in various conditions. Different xanthan gums were first characterised in order to understand the relationship between the structure and rheological and thermal properties before studying more complex systems such as xanthan and particulate materials (cellulosic materials and starch) or konjac glucomannan (KM); all this being the basis of the investigation of the xanthan-KM system in a yeast-raised product. Thanks to a range of xanthans with diverse acetate and pyruvate content coming from two different strains, it was demonstrated that the xanthan structure, especially the pyruvate groups, influences the rheological and thermal properties of xanthan. New findings showed that different master curves (viscosity vs c[rd) were obtained depending on the rigidity of the xanthan and ionic environment as well as the pyruvate groups being the driving force determining the xanthan viscosity and transition temperature. The pyruvate groups and their distribution also influence its interaction with konjac mannan leading to two types of interactions (with ordered and disordered form of xanthan) within a single xanthan sample. However, the optimum ratio of xanthan:KM present in aqueous solutions is not present in a food product (bread), but the different effect of xanthan and KM is noticeable: dough strength, and open structure of the breadcrumb for xanthan and dough extensibility and dryness for KM. The mixture of these hydrocolloids produced more acceptable breads than those made with only xanthan or KM.

Statistical Process Control (SPC) is an effective technique improving process performance in manufacturing companies; however, the literature shows its implementation in the food industry is still less evident. This research aims to assess the SPC implementation in the UK food industry and subsequently develops an SPC implementation roadmap (SPCIR) and SPC Readiness Self-assessment Tool for food companies to assess their readiness level to adopt SPC. Survey and multiple-case studies were conducted to identify the widespread of SPC, challenges of implementing SPC, Critical Success Factors and the reasons for not implementing SPC in this industry. A five-phase SPCIR was refined through the action research, while five SPC readiness factors were identified through the Delphi study. This study adds value to the current knowledge by extending organisational readiness theories through the identification of SPC readiness factors and expands the organisational learning theory by uncovering type of learning created within SPC implementation. This study is relevant, practical, and useful to both practitioners and academics by providing a holistic implementation roadmap to guide the managers to implement SPC not only at the organisational level but also at the project level. This study offers an itinerary of organisational readiness that enables the managers to confirm the organisational preparedness for the adoption of SPC. The small sample size may limit the generalisability of the findings. But this exploratory study provides critical information to the managers in this sector to develop a strategic plan for a successful SPC implementation.

The influence of thermal processing and preservation techniques on selected bioactive compounds of baobab fruit pulp and juice from Malawi were analysed using RP-HPLC whereas total phenol content (TPC) and antioxidant activity were measured by spectrophotometry. 1H NMR-based metabolomics was used to compare the metabolic profile of untreated (UT), high temperature short time (HTST) pasteurised and high temperature short time pasteurised with added citric acid (CAHTST) baobab juice samples and to analyse the temporal changes upon different storage conditions. Malawi baobab pulp contains high levels of procyanidin B2 (533.3 ± 22.6 mg/100 g FW), vitamin C (465.8 ± 2.5 mg/100 g FW), gallic acid (68.5 ± 12.4 mg/100 g FW) and (-)-epicatechin (43.0 ± 3.0 mg/100 g FW) and showed high TPC and antioxidant activity. Vitamin C content of dry baobab pulp and 10% juice (w/v) was retained during heat treatment by microwaving and pasteurisation (72 °C, 15 s) respectively. However vitamin C level in pasteurised juice significantly decreased during storage compared to untreated control, suggesting the demand for advanced processing methods including non-thermal pasteurisation. Seed liquor enhanced phenolic compounds in the juice but its influence on vitamin C needs further investigation. Principal Component Analysis (PCA) of 1H NMR data produced distinct clusters separated according to treatment and storage conditions. For HTST and CAHTST juice samples, the most important accumulating metabolites were fructose, glucose and galacturonic acid, while sucrose decreased over time. The more rapid production of ethanol in UT juice is a clear indication that pasteurisation of juice alone or in combination with the addition of citric acid can minimise fermentation in baobab juice. Results from this study will enhance understanding of composition of baobab fruit products and promote development of quality novel functional foods to tackle malnutrition as well as expand market opportunities for Malawi.

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