Modeling water and counterion partition in composite gels of BSA with gelatin following thermal and high pressure treatment
Creators: name: SEMASAKA, Carine
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 300602
subject: Food chemistry and food sensory science

description: Phase separation between biopolymers is a critical parameter determining the physical characteristics of food products. Knowledge on the structure-function relationship of biopolymer mixtures is important for the development of materials with desirable textural properties and stability. Despite the increasing appreciation of biopolymers in imparting techno-functionality in a wide range of materials, including foods and nutraceuticals, there have been drawbacks in recording directly the water and counterion partition between two hydrocolloid phases which determine the structural properties of the aqueous material in many food products. <br><br>In an endeavour to understand such processes, this study provided experimental evidence and modeled the solvent as well as counterion partition in thermally and high pressure treated mixtures of bovine serum albumin (BSA) with gelatin suggesting the importance of network characteristics and geometrical organization of the two polymer phases in governing water and counterion partition within this binary system. This study sought to further advance the understanding of these systems by using differential scanning calorimetry, small deformation dynamic oscillation techniques, scanning electron microscopy and Fourier transform infrared spectroscopy to characterise the single systems as well as their binary mixtures.<br><br>In the first experimental chapter, BSA/gelatin mixtures were subjected to a series of thermal treatment, i.e. cooling, isothermal at low temperature, heating, isothermal at high temperature and a second cooling step. Such protocols encourage formation of different micro phase-separated materials; the first cooling yielded continuous gelatin structure with BSA liquid inclusions, heating the systems produced continuous BSA matrix supporting liquid gelatin, then the second cooling yielded isotropic two-phase gel. Lewis and Nielsen equations were successfully applied on the mixture with a dispersed liquid phase whereas isostrain-Isostress blending laws were successfully used for the composite gels with the solid filler inclusions. The results argued that the component that forms the continuous phase has a higher water affinity than the discontinuous filler. It is postulated that the continuous network inhibits diffusion of water molecules to the discontinuous phase.<br><br>In the second experimental chapter, work was advanced to understand the effect of counterion in the form of calcium chloride (CaCl2), on the structural properties of BSA/gelatin composites. Similar to the previous chapter, a series of cooling, heating and subsequent cooling routine were employed to produce phase separated BSA/gelatin blends. A critical issue was the inability to know exactly how much counterion each phase was able to attract. To address this issue, the blending laws normally used to predict the composition and volumes of the phases in hydrogels in relation to solvent partition were modified and adapted for the partition of counterion between the two polymeric phases. Results from this study show, for the first time, that the blending laws (Takayangi and Lewis-Nielsen), can successfully be used to estimate the counterion partition in these mixtures. In general, it was found that the counterion was preferentially held in the biopolymer that formed the continuous network.<br><br>In the third experimental chapter, high pressure (300MPa for 15min) was applied to this system in order to pinpoint alterations in physiochemical properties and solvent partition in single preparations of BSA, gelatin and their binary mixtures. It was also documented that pressurized mixtures of gelatin and BSA yielded phase separated systems; pressurization at low temperature (10°C) allowed gelatin to gel and formed the continuous phase with BSA as the liquid inclusions, whereas pressurization at high temperature (80°C), the denatured BSA gelled and formed the continuous phase supporting the liquid gelatin phase. The experiments also included a comparison of pressurized and unpressurized systems. Application of Lewis-Nelson equations argued that the solvent partition was always in favour of the polymer which formed the continuous phase. These outcomes were contrasted with our earlier findings on unpressurized systems and the solvent partition concept (p-factor) proved that unpressurized samples exhibited more favourable affinity for water molecules (more than 3 times) compared their pressurized counterparts. This was the first attempt that blending laws theories were successfully applied on pressurized hydrogels to elucidate the water distribution in the biphasic systems.<br><br>The last experimental chapter explored the effect of CaCl2 on the phase behaviour of pressurized BSA/gelatin. The same techniques were used to characterize the structural properties of the systems. It was also found that pressurization of BSA and gelatin in the presence of CaCl2 phase separated, with gelatin forming the continuous network with BSA liquid inclusion following pressurization at low temperature, whereas BSA formed the continuous phase with gelatin liquid inclusion following pressurization at high temperature. Once again, the Lewis-Nielsen equations, hitherto employed only in relation to the water avidity of composite gels, were successfully adapted to consider every possible distribution of the counterion between the two polymeric phases of the pressurized materials. The approach allowed introduction of a new concept called counterion partition factor (pc) as a measure of the relative attraction between polymer and counterion in a binary system. In the case of gelatin and BSA, the results argued that the biopolymer that formed the continuous phase would always retain dynamically disproportionate amounts of calcium ions on a weight-for-weight basis.<br><br>Thus, this study is particularly important in providing information on the phase behaviour of mixed systems of gelatin and BSA subjected to heat and high pressure treatments. Such information will offer a real benefit to food industries where it can be widely used in protein based formulations. Therefore, this research provides information which will help in improving manufacturing processes and development of added value products.