No abstract

The goal of this work was to investigate the dynamics of human plasma fibronectin (HFN) at the oil-water interface and to characterize its interactions with human serum albumin (HSA) by total internal reflection fluorescence microscopy (TIRFM). Among key results, we observed that fibronectin adsorption at the oil-water interface is rapid and essentially irreversible, even over short time scales. This may be due to the highly flexible nature of the protein, which allows its various domains to quickly attain energetically favorable conformations. On the other hand, HSA adsorption at the oil-water interface is relatively reversible at short times, and the protein is readily displaced by fibronectin even after HSA has been adsorbed at the interface for as long as 2 h. At longer adsorption times, HSA is able to more effectively resist complete displacement by fibronectin, although we observed significant fibronectin adsorption even under those conditions. Displacement of adsorbed fibronectin by HSA was negligible under all conditions. Fibronectin also adsorbs preferentially from a mixture of HFN and HSA, even when the concentration of HSA is substantially higher. This study is relevant to such emerging research thrusts as the development of biomimetic interfaces for a variety of applications, where there is a clear need for better understanding of the effects of interfacial competition, adsorption time scales, and extent of adsorption irreversibility on interfacial dynamics.

The goal of this work was to measure and model the effect of thermal exposure on the fluorescence emission of R-phycoerythrin (R-PE). The long-term objective of our work is to assess the feasibility of encapsulating R-PE for use as the critical component of a time-temperature integrator (TTI) for ascertaining the degree of inactivation of food pathogens such as Salmonella. In this article we present a study to measure and model the thermally induced fluorescence emission decay of R-PE in several isothermal experiments. We used the isothermal data to determine the kinetic parameters, based on a general n(th) order reaction, and evaluated the utility of the resulting model by using it to predict R-PE fluorescence emission decay for several nonisothermal experiments based on published USDA safe harbor guidelines for cooked beef products. The transient experiments were conducted over the same temperature range used in the isothermal study. Very good agreement was obtained between theory and experiment at temperatures of 62.8 degrees C and above, although the model slightly underpredicted the extent of fluorescence emission decay at 60 degrees C. Our results indicate that R-PE fluorescence emission decay kinetics is well behaved and that the protein is a strong candidate for use as a time-temperature integrator.