Studies on selected physicochemical properties and microstructure of β-casein-enriched ingredients for applications in formulated nutritional products

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Li, Meng
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University College Cork
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The milk protein β-casein (β-CN) possesses excellent functional properties and is the most abundant casein in human milk. Therefore, β-CN has the potential to be used as an ingredient in nutritional food applications, in particular in infant formulae (IF). However, the manufacture of β-CN products using various feed materials and enrichment approaches can lead to considerably differences in the overall composition and purity of β-CN in such ingredients. These differences would be expected to influence the physicochemical and functional properties of β-CN ingredients and their formulated nutritional products. This thesis presents an investigation of the physicochemical and microstructural properties of three different β-CN products (pure β-CN [β-CNpure, β-CN=90% of total protein], β-CN concentrate [β-CNconc, 80% purity], β-CN-enriched ingredient [β-CNen, 58% purity]) in different dairy systems (solutions, emulsions and model IF). The results of this work demonstrated that the three β-CN products exhibited different thermal-induced association behaviour, which was highly dependent on the purity and composition of β-CN products, along with the presence of ionic calcium and phosphates. Both β-CNpure and β-CNen showed significantly lower surface/interfacial tension compared to whey protein isolate (WPI), indicating the excellent surface-active properties of β-CN. The stability of 10% oil-in-water (O/W) emulsions stabilised with 0.5% β-CNconc was strongly dependent on the state of association of β-CN in aqueous solution. β-CNpure was covalently labelled using a fluorescent dye (NHS-Rhodamine) and the mixture of labelled β-CN and WPI (1:1 w/w) was employed as an emulsifier in O/W emulsions. Combining covalent and generic labelling techniques with confocal laser scanning microscopy (CLSM) allowed simultaneous visualisation of β-CN and WPI at the interface of oil droplets. β-CN-enriched model IF were also produced with β-CNen and WPI at various whey protein:casein ratios in the range 100:0-0:100, where the model IF enriched with β-CNen better reflected the protein profile of human milk. Increasing the proportion of β-CNen increased the stability and viscosity of IF and decreased the wettability and dispersibility of β-CNen IF powders. Overall, the findings of these studies are of relevance to end-users of β-CN-enriched products in controlling the association behaviour of β-CN and improving the stability of nutritional products enriched with β-CN.
β-casein , Emulsion , Aggregation , Microscopy
Li, M. 2020. Studies on selected physicochemical properties and microstructure of β-casein-enriched ingredients for applications in formulated nutritional products. PhD Thesis, University College Cork.