Diffusion of nicotinic acid in spray-dried capsules of whey protein isolate

Diffusion patterns of nicotinic acid were evaluated following its microencapsulation into a whey protein matrix through spray drying. Micro-differential scanning calorimetry, small-deformation rheological techniques, wide-angle X-ray scattering, Fourier transform infrared spectroscopy, particle size analysis and scanning electron microscopy were utilised to characterize encapsulant and bioactive compound in the composite material. UV vis spectroscopy, the newly introduced concept of spectroscopic shift factor and the Konig reaction were also employed to elucidate the rate of vitamin transport throughout the polymeric matrix as a function of a broad time and temperature spectrum. Mechanical properties of the condensed matrix followed a progression that was described with the combined Williams-Landel-Ferry/free volume theory leading to the prediction of the mechanical glass transition temperature. Modified Arrhenius equation demonstrated that the kinetics of nicotinic-acid mobility were distinct from the structural relaxation of the polymeric segments. The former was further examined using the second law of Fickian diffusion. A direct relationship between fractional free volume of the whey protein network and diffusion coefficient of the nicotinic acid was established within the experimental temperature range.