Journal Articles

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Has files: YesSubject: search.filters.subject.Colloidal aggregation

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    Tuning heat-­‐induced colloidal aggregation of whey proteins, sodium caseinate and gum arabic: effect of protein composition, preheating and gum arabic level
    (ELSEVIER SCI LTD, 2014) Loveday, SM; Ye, Aiqian; Anema, Skelte G; Singh, Harjinder
    Heating can drive the colloidal complexation of negatively-­‐charged proteins and polysaccharides by strengthening hydrophobic interactions and denaturing proteins, thereby exposing reactive sites for covalent and noncovalent bonding. We have previously shown that stable colloidal aggregates comprising whey protein, sodium caseinate and gum arabic can be produced by careful selection of heat treatment, pH and protein type. Here we tested how the size, composition, charge and morphology of colloidal aggregates are affected by the amounts of whey protein, sodium caseinate and gum arabic, as well as the thermal history of the proteins. Increasing amounts of whey protein resulted in larger particles, which were more prone to precipitate. Preheating whey protein slightly enhanced aggregation, and this effect was mitigated when sodium caseinate was present during preheating (chaperone effect). Increasing amounts of gum arabic produced larger particles with less charge, but the gum arabic effect was statistically confounded with ionic strength. We believe that both covalent (disulphide) and noncovalent interactions among protein molecules are required to overcome electrostatic repulsion at pH 7 and form stable aggregates.
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    Heat-induced colloidal interactions of whey proteins, sodium caseinate and gum arabic in binary and ternary mixtures
    (Elsevier Ltd, 2013-11) Loveday SM; Ye A; Anema SG; Singh H
    Many food-grade proteins and polysaccharides will aggregate together when acidified or heated, due to electrostatic and hydrophobic interactions. At low concentrations, aggregates are soluble and colloidally stable, and they have potential applications as Pickering emulsifiers and nutrient carriers. Sodium caseinate (SC) and gum arabic (GA) at pH. 7 will form colloidal aggregates when heated, but aggregation is largely reversed on cooling. Whey proteins (in the form of whey protein isolate, WPI) will aggregate irreversibly with GA when they are heated together, but aggregation is often so rapid and extensive that aggregates precipitate. Here we sought to overcome those limitations, and to develop an in situ method for quantifying heat-induced aggregation. Aggregation was measured using temperature-controlled dynamic light scattering equipment and transmission electron microscopy. Combinations of SC, WPI and GA were heated at either pH. 7 or 3.5, and the weight ratio of protein to polysaccharide was held at 1:5 for simplicity. Heat-induced colloidally stable aggregates of SC. +. WPI. +. GA did not dissociate on cooling. Aggregation was measured in situ, both in temperature ramps and with isothermal experiments. In situ measurement allowed us to avoid potential artefacts stemming from the temperature changes and measurement delays associated with ex situ measurements. This work demonstrated how the size and heat-stability of colloidal protein-polysaccharide aggregates can be tailored by judicious selection of proteins, pH and heat treatment.