Fundamental studies of vitamin diffusional mobility in high-solid hydrocolloids matrices
Creators: name: Panyoyai, Naksit
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 300602
subject: Food chemistry and food sensory science

description: Whilst it has been long known that bioactive compounds can be preserved within a high-solids environment, the precise nature of the effect of processing time and temperature on bioactivity and its delivery is not entirely understood. This thesis has been designed to provide fundamental information on the kinetics of vitamin release from high-solid hydrocolloid matrices. Mathematical modelling based on high-utility empirical relations in combination with theoretical schools of thought has considerable potential for innovative product development and is employed presently. To understand the molecular interactions of ascorbic acid in a high methoxy pectin/polydextrose and thiamine in k-carrageenan/glucose syrup systems, we utilised the combined framework of free volume theory with the concept of effective diffusion coefficient. Our modelling has taken into account the amorphous nature of the polymeric matrices, which are cable of forming cohesive three dimensional networks, their geometry and the direction of diffusion pathways for the bioactive compounds within the surrounding solid-like environment. Improved understanding of the underlying molecular process was achieved by relating the network glass transition temperature to release patterns of the vitamins within the structured matrices. This free-volume driven effect is further modelled with a diffusion mechanism for delivery of the vitamins.<br><br>This study also develops a systematic protocol of experimentation and theory to rationalise the diffusional patterns of nicotinic acid in whey protein and tocopheryl acetate in modified waxy maize starch microcapsules, but outcomes should have generic interest in the structural relaxation of polymer-vitamin composites. Industrial application may emanate from the use of spray drying to achieve multiple droplets processing into high-solids systems with well characterised techno-functionality. It is thus documented that vitamin encapsulating matrices are amorphous in nature with a well-defined mechanical glass transition temperature (Tg). The concept of free volume is operative in the viscoelastic functions of the glassy matrix whose relaxation is distinct from the diffusional mobility of the microconstituent. Temperature variability in the transfer of the vitamin was conveniently analysed with Fick’s second law to unveil the effective diffusion coefficient. This is affected by the vitrification state of the polymeric networks. Indeed, it is quite remarkable that a comprehensive relationship between free volume of the polymeric chain segments and diffusion rates of both vitamins was achieved in this work.<br><br>In conclusion, the four experimental chapters of this thesis have documented the presence of a mechanical Tg in hydrocolloid systems, and this have been modelled with the WLF equation/free volume theory. This has then formed the basis for a study of the inclusion of vitamins and monitoring their diffusional mobility from high solid matrices. Evidence of non-Fickian phenomena was observed that allowed estimation of the effective diffusion coefficient in these systems. It became apparent that the literature lacked rigorous analysis of the relationship between matrix free volume and effects on the transport phenomena of microconstiuents. Thus, the contribution of the research is to develop such a relationship based on current experimental results and theoretical treatments in order to discuss potential applications to systems with industrial interest.