期刊
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
卷 51, 期 6, 页码 1658-1665出版社
AMER CHEMICAL SOC
DOI: 10.1021/jf020784v
关键词
oil-water interface; kinetics of protein adsorption; competitive adsorption; thermodynamic incompatibility at interfaces; alpha(s)-casein; beta-casein
Competitive adsorption of alpha(s)-casein and beta-casein from a bulk solution mixture to the triolein-water interface has been studied. Although the binding affinity of as-casein to the triolein-water interface was lower than that of beta-casein in single-component systems, in a 1:1 mixture of alpha(s)-casein and beta-casein in the bulk solution the ratio of interfacial concentrations of alpha(s)-casein to beta-casein at equilibrium was about 2:1, indicating that alpha(s)-casein was preferentially adsorbed to the triolein-water interface. Furthermore, the equilibrium composition of as-casein and beta-casein in the interfacial film at various bulk concentration ratios did not follow a simple Langmuir adsorption model. This deviation from ideal behavior was mainly due to thermodynamic incompatibility of mixing of these caseins in the interfacial region. The value of the incompatibility parameter, X-12, for these caseins at the triolein-water interface was much greater than that at the air-water interface. Displacement experiments showed that while alpha(s)-casein could dynamically displace beta-casein when the latter was in an unsaturated monolayer state at the interface, it could not do so when beta-casein was in a saturated monolayer film state. It is hypothesized that, because of thermodynamic incompatibility of mixing, the alpha(s)-casein and beta-casein mixed film at the oil-water interface may undergo two-dimensional phase separation.
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