The core technological hurdles limiting the use of whey protein ingredients in value-added nutritional beverages include poor solubility, heat stability and lack of clarity, particularly in high-acid or high ionic strength, ready-to-drink systems such as those found in sports and performance nutritional products. The studies in this thesis detail novel research into production, characterisation and functional properties of whey proteins/peptides conjugated with a range of starch hydrolysis products. Targeted structural modification of the components, e.g., hydrolysis of the whey proteins, or increasing dextrose equivalent value of the starch hydrolysis products, increased the rate of protein-carbohydrate conjugation on wet heating (initial pH 8.2, 90ºC). The heating mode also influenced the rate and extent of conjugation; an equivalent level of conjugation was achieved on dry heating of WPI with maltodextrin (MD) under milder conditions (60ºC and 79% relative humidity for 24 h) compared to wet heating for 8 h. Solutions of conjugated whey proteins/peptides had improved solubility and thermal stability compared to the respective unconjugated control solutions; this was attributed to the covalent attachment of starch hydrolysis products to the proteins/peptides. Dry heating of WPI with MD maintained the native structure of the whey proteins while increasing both the protein solubility and thermal stability, compared to untreated whey protein. The influence of aggregation state on availability of amino groups in whey proteins was investigated; sulfhydryl-disulphide interchange and disulphide-bond mediated aggregation of whey proteins resulted in decreased availability of amino groups as measured by the o-phthalaldehyde (OPA) and trinitrobenzenesulfonic acid (TNBS) methods due to the amino groups being located within large, dense protein aggregates. Overall, the findings presented in this thesis constitute a significant advancement of the body of knowledge on whey protein/peptide-carbohydrate conjugate ingredients, specifically in terms of optimising their preparation and studying their functional characteristics to facilitate their incorporation into food formulations.
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