| Conjugated linoleic acid(CLA) is one of the unsaturated fatty acids that have many bioactivities. It is liable to be oxidated when exposed to light, heat and oxygen. CLA emulsions stabilized by biopolymer could improve the oxidative stability of CLA and could extend CLA applications in foods. This paper is focused on the following aspects: the interfacial adsorption of three gum Arabic samples(conventional gum: GA and two matured gums: EM2 and EM10) at the CLA-water interface was investigated in relation to their emulsifying properties. Afterthat, whey protein isolate(WPI) is introduced to study the electrostatic interaction of WPI/GA system by dynamic light scattering and turbidity measurements, in order to determine the experimental parameters for the formation of WPI/GA intramolecular complexes. The physical and chemical stabilities of CLA emulsions stabilized with WPI/GA intramolecular complexes were evaluated. In addition, the influence of ionic strength on the interaction between WPI/GA and emulsion stability were also investigated. The emulsifying properties and emulsion stability of WPI/GA intramolecular complexes stabilized CLA emulsions were evaluated at different ionic strength. The main conclusions are as follows:1) The best emulsifying performance of the three kinds of gum arabic was found at a gum concentration of 5.0%, where maximum surface load was achieved. AGP fraction was the major component that adsorbed on to the emulsion interface, and therefore its content determined the difference in emulsifying activity for GA, EM2 and EM10. EM10 conferred the best stability for CLA emulsions. It could be mainly attributed to a larger tendency of AGP toward aggregation at interface in EM10-stabilized emulsion.2) The maximum stoichiometry of WPI/GA is about 1.0. When WPI/GA mixing ratio(r) > 1.0, the possible binding sites of GA are fully occupied by excessive WPI molecules. The excessive WPI could affect the interaction of WPI/GA via bridging flocculation. When r < 1.0(polysaccharide in excess), the possible binding sites of WPI are fully occupied by excessive GA molecules. The free carboxylic groups(unoccupied binding sites) of GA make the complexes negatively charged. The stable and soluble intramolecular complexes could form at r = 0.5 and p H 4.20-4.83.3) The emulsifying properties and emulsion stabilities of CLA emulsions are improved by stabilizing with WPI/GA intramolecular complexes. The average diameter of CLA emulsions stabilized with 2.0% WPI/GA intramolecular complexes reaches the minimum. CLA emulsions stabilized with WPI/GA intramolecular complexes displayed better physical and chemical stabilities than those with WPI and GA alone, resulting from a typical synergistic adsorption.4) The addition of Na Cl has a strong effect on the interaction of WPI/GA. p Hc(the onset of light scattering increase) and p Hφ(the maximum of light scattering) decreased with increasing the Na Cl concentration. It is suggested that the formation of WPI/GA electrostatic complexes has been inhibited, attributed to the electrostatic screening of Na Cl. The addition of Na Cl had an adverse effect on the physical stabilities of the CLA emulsions stabilized with WPI/GA intramolecular complex. The average diameter of CLA emulsions increased with increasing Na Cl concentration, resulting in a decrease in emulsions stability. Key: Conjugated linoleic acid; Electrostatic complexes; Emulsions; Stability... |
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