Investigation of surface modification of casein films by rennin enzyme action using micro-beam grazing incidence small angle X-ray scattering

Abstract

Micro-beam grazing incidence small angle X-ray scattering (μGISAXS) scans were performed to investigate structural changes that occur after deposition of a droplet of rennin on a casein film. The subsequent diffusion of the droplet into the film led to a lateral and vertical concentration gradient of rennin. As a result of the enzyme action, the film surface became roughened and the formation of islands — evident. The altered surface morphology led to a variation in the μGISAXS pattern, more precisely to the occurrence of a second so-called Yoneda peak. As for the untreated casein film, the mean size of the micelle components (casein micelles, substructure and colloidal calcium phosphate) remained constant within the rennin droplet area. In contrast, a broadening of their corresponding size distributions could be detected. Finally, we discuss the potential of GISAXS scanning experiments with micrometer-sized X-ray beams in view of problems with the interpretation of the data obtained from imaging techniques such as atomic force microscopy.