Naksit Panyoyai

Effect of sodium chloride on the glass transition of condensed starch systems.

The present investigation deals with the structural properties of condensed potato starch-sodium chloride systems undergoing a thermally induced glass transition. Sample preparation included hot pressing at 120°C for 7 min to produce extensive starch gelatinisation. Materials covered a range of moisture contents from 3.6% to 18.8%, which corresponded to relative humidity values of 11% and 75%. Salt addition was up to 6.0% in formulations. Instrumental work was carried out with dynamic mechanical analysis in tension, modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and wide angle X-ray diffraction. Experimental conditions ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of sodium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Sodium ions interact with chemical moieties of the polysaccharide chain to alter considerably structural properties, as compared to the starch-water matrix.

Controlled release of thiamin in a glassy κ-carrageenan/glucose syrup matrix.

The work dealt with the diffusional mobility of thiamin embedded in a high-solid matrix of κ-carrageenan with glucose syrup. It utilized thermomechanical analysis in the form of modulated differential scanning calorimetry and small-deformation dynamic oscillation in shear, Fourier transform infrared spectroscopy, wide angle X-ray diffraction, scanning electron microscopy and UV-vis spectrophotometry. The structural properties of the matrix were assessed in a temperature induced rubber-to-glass transformation. A thiamin-dye binding assay was employed to monitor the diffusion process of the vitamin from the high-solid preparation to ethylene glycol. The relationship between mechanical properties of the carbohydrate matrix and vitamin mobility was assessed via the application of the combined framework of the free volume theory and the predictions of the reaction rate theory. Results argue that the transport of the micronutrient is governed by the structural relaxation of the high-solid matrix. These were further treated with the concept of Fickian diffusion coefficient to provide the rate of the bioactive compound mobility within the present experimental settings.

Effect of salt on the glass transition of condensed tapioca starch systems

This work examines the effect of including hydrated NaCl and CaCl2 (up to 6% w/w) on the physicochemical properties of condensed tapioca starch. Samples were prepared by hot pressing at 120°C to produce condensed systems that covered a range of moisture contents from 7.34% w/w (23% relative humidity) to 19.52% w/w (75% relative humidity). Tensile storage modulus and heat flow measurements were taken using DMA and MDSC, which were accompanied by FTIR, WAXD and ESEM. Increasing the salt level enhances the mechanical strength of starch in the glassy state and shifts the glass transition temperature to a higher value. Antiplasticising effects of NaCl and CaCl2 on the non-phosphorylated tapioca starch are indistinguishable from each other. Observations are complemented by intensification of absorbance peaks in FTIR spectra and a systematic change in shape and intensity of diffraction patterns with increasing addition of salt consistent with interactions between added ions and macromolecule.

Calcium chloride effects on the glass transition of condensed systems of potato starch

The effect of calcium chloride on the structural properties of condensed potato starch undergoing a thermally induced glass transition has been studied using dynamic mechanical analysis and modulated differential scanning calorimetry. Extensive starch gelatinisation was obtained by hot pressing at 120°C for 7 min producing materials that covered a range of moisture contents from 3.7% w/w (11% relative humidity) to 18.8% w/w (75% relative humidity). FTIR, ESEM and WAXD were also performed in order to elucidate the manner by which salt addition affects the molecular interactions and morphology of condensed starch. Experimental protocol ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of calcium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Highly reactive calcium ions form a direct interaction with starch to alter considerably its structural properties via an anti-plasticizing effect, as compared to the polymer-water matrix.

Tocopheryl acetate release from microcapsules of waxy maize starch

Diffusion coefficients are utilised to provide a realistic approach in the quantification of mass transport phenomena, which are important for the delivery of bioactivity from high-solid biopolymer systems. Following this mechanistic consideration, we employ spray drying to produce microcapsules of waxy maize starch that suspend homogeneously tocopheryl acetate. An array of physicochemical techniques including dynamic oscillation in-shear or compression mode, microDSC, WAXD, FTIR, scanning electron or optical microscopy, and UV-vis assays were utilised to relate structural properties of the macromolecular network to diffusivity of the bioactive compound. A modified version of the free-volume theory designed to address molecular diffusion was evaluated over a wide temperature range. Predictive capabilities were facilitated by proposing a mathematical relationship between diffusion coefficient of tocopheryl acetate and fractional free volume of waxy maize starch. Moreover, the theoretical approach is able to accurately describe the extent of cooperativity in the vitamin-biopolymer interaction that determines transport kinetics.

Effect of the glass transition temperature on alpha-amylase activity in a starch matrix.

This study optimises a protocol for the estimation of α-amylase activity in a condensed starch matrix in the vicinity of the glass transition region. Enzymatic activity on the vitrified starch system was compared with that of a reference substrate, maltodextrin. The activity was assayed as the rate of release of reducing sugar using a dinitrosalicylic acid procedure. The condensed carbohydrate matrices served the dual purpose of acting as a substrate as well as producing a pronounced effect on the ability to enzymatic hydrolysis. Activation energies were estimated throughout the glass transition region of condensed carbohydrate preparations based on the concept of the spectroscopic shift factor. Results were used to demonstrate a considerable moderation by the mechanical glass transition temperature, beyond the expected linear effect of the temperature dependence, on the reaction rate of starch hydrolysis by α-amylase in comparison with the low-molecular weight chain of maltodextrin.

Physicochemical and viscoelastic properties of honey from medicinal plants

The present work investigated the physicochemical and structural properties of Tulsi, Alfalfa and two varieties of Manuka honey derived from medicinal plants. Chemical analysis yielded data on the content of reducing sugars (glucose and fructose) that dominate the honey matrix, and of the minor constituents of protein, phenols and flavonoids. Standard chemical assays were used to develop a database of water content, electrical conductivity, pH, ash content, visual appearance and colour intensity. Physicochemical characteristics were related to structural behaviour of the four honey types, as recorded by small-deformation dynamic oscillation in shear, micro- and modulated differential scanning calorimetry, wide angle X-ray diffraction and infrared spectroscopy. The preponderance of hydrogen bonds in intermolecular associations amongst monosaccharides in honey yields a semi-amorphous or semi-crystalline system. That allowed prediction of the calorimetric and mechanical glass transition temperatures that demarcate the passage from liquid-like to solid-like consistency at subzero temperatures.

Structure and phase behaviour of microcrystalline cellulose in mixture with condensed systems of potato starch

It has been suggested that microcrystalline cellulose (MCC) can be used in biodegradable films to improve techno-functionality by providing bulk and enhancing mechanical strength. This study aimed to investigate the effect of MCC addition on the structural properties of potato starch films. Samples were prepared by hot pressing at 120 °C for 7 min to produce systems that covered a broad range of moisture content and relative humidity. Complimentary experimental techniques, including thermomechanical analysis, FTIR, wide-angle X-ray diffraction and SEM, were employed to examine the micro- and macromolecular characteristics in these mixtures. Both moisture content and the presence of MCC have a plasticising effect on the composites yielding a reduction in its glass transition temperature. It appears that there is no specific and nontrivial interaction between potato starch and MCC, an outcome which indicates that the cellulose fibres act as inert filler in the polymeric composite.