The application of powerful tools such as grazing incidence small angle X-ray scattering (GISAXS) equipped with a micrometer-sized beam (µGISAXS) with synchrotron radiation and scanning techniques to investigate the microstructure of casein film surfaces is described. Contrary to real space techniques such as atomic force microscopy and electronic microscopy, a two-dimensional intensity distribution profile is measured by GISAXS. Both a reflected signal and a diffusely scattered signal contribute to the GISAXS profile. The diffusely scattered signal allows details about the shape, size and size distribution of particles to be elucidated by fitting structural models to the data. In this study, structural changes, deliberately induced on a prepared casein film by the addition of rennin, were detected and assessed using µGISAXS. In order to correlate structural information of casein micelles with the microstructure of a rennin modified casein film surface, µGISAXS scans were performed with a step size of 5 µm. The results revealed an altered film surface morphology and structural changes of casein micelles towards para-casein micelles due to the diffusion limited migration and action of rennin within the casein film.

 

Anne Thierry, Editor-in-Chief

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