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- ItemDairy ingredients-based emulsions and beta-carotene delivery(University College Cork, 2018) Lu, Wei; Kelly, Alan; Miao, Song; Chinese Government Scholarship; Teagasc; University College CorkInstability and water-insolubility of many bioactive nutrients greatly limit their oral bioavailability and thus their health benefits. Therefore, the delivery of these compounds requires protective mechanisms. Emulsion-based delivery systems are becoming some of the most ideal microencapsulation carriers for these lipophilic bioactive components, and tailored structures of emulsions potentially contribute to a better control of the stability and bioavailability of instable and poorly water-soluble bioactive components. The current study mainly investigated four model O/W emulsions with different initial droplet size, oil phase compositions, emulsifiers, and water phase compositions. A representative lipophilic bioactive nutrient, β-carotene, was encapsulated into these model emulsions. Emulsion properties, and the in vitro digestion, release, bioaccessibility and absorption by enterocytes of encapsulated βcarotene were investigated. Re-dispersible dry forms of these model emulsions containing β-carotene were also prepared, and their microstructures, re-dispersibility, and the properties of their reconstitutions were characterized. A whey protein isolate (WPI) stabilized emulsion with small initial droplet size showed better creaming and pH stability and higher cellular uptake of β-carotene than that with large initial droplet size. After passing through the simulated gastrointestinal tract (GIT) digestion, initial droplet size significantly influenced the emulsion properties (e.g., droplet size and distribution and surface charge), but did not significantly affect the bioaccessibility and cellular uptake of β-carotene. Monoglycerides (MG) in the oil phase showed competitive absorption on the droplets surface with WPI, leading to reduced droplet surface charge. MG significantly increased the viscosity and creaming stability of WPI-stabilized emulsions. MG also significantly promoted the bioaccessibility and cellular uptake of β-carotene by Caco-2 cells (p<0.05). Emulsions stabilized with different emulsifiers of WPI, sodium caseinate, or tween 80, showed different droplet sizes, surface charges, creaming and pH stability, and cellular uptake of β-carotene without passing through the GIT. Selection of emulsifiers also significantly modified the emulsion properties when exposure to the GIT digestion, and the bioaccessibility and cellular uptake of β-carotene after the GIT digestion (p<0.05). Incorporation of KGM into the water phase of emulsions greatly improved the creaming and pH stability of WPI-stabilized emulsions, and significantly decreased the oiling-off of the emulsions during a freeze-thaw test. Emulsions containing KGM in the water phase showed a lower final release rate of encapsulated β-carotene then the emulsion without KGM (p<0.05), and the release rate decreased with increasing KGM content. Dried emulsions showed different morphologies and microstructures, depending on the drying method (spray-drying or freeze-drying), and the compositions of emulsions before drying. Dry emulsions showed fast re-hydration and good re-dispersibility in water. Compared with emulsions before drying, re-constituted spray-dried and freeze-dried emulsions showed shifted droplet size distribution to large and small size, respectively. Re-constituted emulsions containing KGM showed significantly decreased viscosity but increased creaming stability compared to emulsions before drying (p<0.05). Overall, the present study provided useful information about different model O/W emulsions as delivery carriers for lipophilic components, and on how emulsion structures can be designed to modify the release of health-beneficial lipophilic components and improve their oral bioavailability, which could be important in developing functional foods with sustained release, or improved oral stability and bioavailability of functional ingredients entrapped in food matrixes.
- ItemGhrelin system signalling in appetite and reward: in vitro and in vivo perspectives(University College Cork, 2018) Howick, Kenneth P.; Griffin, Brendan T.; Schellekens, Harriët; FHI 360The regulation of food intake is one of the most intricate internal balances in mammalian behaviour. Dysregulation of the central mechanisms underlying appetite control and metabolism result in both disorders of under- and over-eating. Disorders of appetite result in significant morbidity and mortality, and represent a major unmet clinical need. The endogenous hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR-1a), have long been known as pharmacological targets for appetite-related and metabolic disorders. Nutraceutical and bioactive peptides offer the opportunity to prevent onset and escalation of lifestyle-associated diseases of appetite and metabolism. However, there is a dearth of clinical evidence to justify the development of many bioactives as nutraceuticals. The potential applicability of dairy-derived bioactives in appetite-related disorders is now becoming increasingly apparent. We investigate whether a dairy-derived hydrolysate can increase GHSR-1a signalling in vitro, and whether this can be translated to evidence of effect in vivo in a pre-clinical model (Chapter 2). Subsequently, by leveraging advanced pharmaceutical technology, we develop a gastro-protective and sustained delivery system with a high payload capacity (Chapter 3). Furthermore, ligand-dependent biased signalling, and ligand biodistribution may have important roles to play in increasing efficacy of ghrelin ligands in vivo. Therefore, we investigate whether two synthetic ghrelin ligands, anamorelin and HM01, exert differential effects on the GHSR-1a in vitro (Chapter 4). The divergent effects of these two ligands on appetite and reward-motivated behaviours, as well as effects on central neuronal activation and reward system dopamine (DA) levels will also be investigated with a view to informing strategies to optimize future ghrelin therapies (Chapter 4 and 5). Chapter 2 and 3 provide an effective platform for gastro-protected delivery of bioactive peptides to enable further proof-of-concept studies across the appetite modulation field. Evidence of an orexigenic effect of the bioactive is seen in vivo in a rodent model. The oral delivery system developed served as a clinical formulation platform for proof-of-concept studies in humans to be conducted within the wider Food for Health Ireland research consortium. Chapters 4 and 5 show the importance of biased signalling and biodistribution of ghrelin ligands. Greater maximal food intake is reported by the brain penetrant HM01 vs. the peripherally limited anamorelin. Divergent neuronal activation of the two ligands is also shown in reward processing areas using c-fos immunostaining. Targeting specific downstream signalling pathways will enable the provision of more efficacious appetite modulation therapies, while centrally penetrant ligands will provide further therapeutic avenues through greater reward system activation.
- ItemMilk bioactives and early infant nutrition(University College Cork, 2019) Mackey, Sinead Marie; Fitzgerald, Gerald F.; Stanton, Catherine; Ross, R. PaulThe gastrointestinal microbiota is established following birth with bifidobacteria present at elevated levels in the gastrointestinal tract of breast fed infants when compared to formula fed infants. This thesis identified two fermented dairy ingredients that enhanced bifidobacterial growth. Additionally, the cultures utilised in the production of the fermented ingredients were further assessed for antimicrobials with one identified. In vitro studies were performed using the fermented ingredients to establish the true extent of the bifidobacterial enhancing capabilities. Further studies confirmed the ability of the ingredients to survive simulated gastrointestinal conditions, while a study using a mixed culture fermentation model confirmed the ability of the fermented ingredients to enhance levels of bifidobacteria in a mixed culture environment. The bacterial fermentates enhanced total bifidobacterial counts to levels that were comparable to those recorded for the control vessel containing Fructooligosaccharides (an ingredient readily utilised in infant milk formula). An animal study was completed and the microbial composition of the mice caecum was assessed for the four study groups following four weeks of feeding the fermented ingredients, FOS and the unfermented control. 454-sequencing technologies confirmed similar levels of lactobacilli and bifidobacteria were present in the caecum, relative to the FOS. Additionally, one of the fermented ingredients reduced levels of the genus Clostridium when compared to the unfermented control. In summary, this thesis describes the generation of two bacterial fermentates which potentially may contribute to gastrointestinal health based on their bifidobacterial enhancing capabilities. One culture was also confirmed to possess a helveticin J bacteriocin. All three are of particular interest as the fermenting starter cultures and the strain possessing the helveticin J are classified as GRAS (generally recognised as safe) and QPS (qualified presumption of safety). Furthermore, the research also describes possible vehicles in which the functional ingredients can be delivered to the gastrointestinal tract.