Complexation of bovine serum albumin and sugar beet pectin: Stabilising oil-in-water emulsions

In a previous study (Langmuir 28 (2012) 10164–10176.), we investigated the complexation of bovine serum albumin (BSA) with sugar beet pectin (SBP). A pH–composition phase diagram was established and structural transitions in relation to the phase diagram during complexation were identified. The present study examines the implications of these interactions on the emulsifying performance of BSA/SBP mixtures. Middle-chain triglycerides (MCTs) in water emulsions were prepared using conditions corresponding to different regions of the phase diagram. At high pHs and in the stable region of mixed individual soluble polymers where complexation is absent, there is no improved emulsifying performance, compared with the individual protein and polysaccharide. For these mixtures, the emulsion characteristics are controlled by the major component in the solutions, as determined by the competitive adsorption of the two components at the oil–water interface. At low pHs and low BSA/SBP ratios, and so mainly within the stable region of intramolecular soluble complexes, BSA/SBP mixtures greatly improve the stability of emulsions. Here, stabilisation is controlled by the cooperative adsorption of the two components at the oil–water interface. Through electrostatic complexation BSA promotes the adsorption of SBP on to interfaces to form a thick steric layer around emulsion droplets and thus providing better stability. At low pHs and high BSA/SBP ratios, that is, mainly within the unstable region of intermolecular insoluble complexes, emulsions prepared are extremely unstable due to bridging flocculation between emulsion droplets.

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► Interfacial behaviours of protein/polysaccharide depend on their phase regions.
► Competitive adsorption onto oil–water interface harms emulsification.
► Cooperative adsorption onto oil–water interface generally improves emulsification.
► Emulsifying performance of sugar beet pectin was improved by incorporating protein.