The characterization of viscoelastic components such as gels or gelation of gelatin heavily depends on the storage modulus (G′) is also known as elastic modulus represents the strength of network, and viscous moduli (G″) which is a measure of the flow properties for the sample in the structured state and is also known as the loss modulus. There is a direct proportionality between the values of storage modulus and the number of interactions and the strengths involved. (Perkins, 2011) Unlike the storage modulus, the value of the viscous modulus is independent of the force of the material and is only related to the number of interactions. Furthermore, phase angle or tan δ is a parameter associated with the degree of viscoelasticity of a sample, tan δ = (G″/G′). A high value of tan δ indicates that the sample is more viscous or liquid–like, while low value of tan δ means that the sample is more elastic or solid–like. The following table (3.5) shows the standard rheological parameter. The ratio of viscous modulus and that of storage modulus results in the generation of the phase angle (tan δ) which gives the extent of viscoelasticity of material.
Table 3.5 Standard rheological parameters
Parameter Definition Symbol Units (SI)
Shear stress Force per unit area  Pa
Shear strain Relative deformation in shear  –
Shear rate Change of shear strain per unit time  ̇ s-1
Viscosity Resistance to flow  Pa.s
Shear storage modulus Measure of elasticity of material G′ Pa
Shear loss modulus The ability of material to dissipate energy G” Pa
Complex viscosity Resistance to flow of the sample in the structure state
originating as viscous or elastic flow
resistance to oscillating movement * Pa.s
Dynamic viscosity Internal friction of a liquid  ̇ Pa.s
Phase angle Degree of viscoelasticity Tan  –

During food processing heat is involved at different steps. The food undergoes different types of transformations, including melting, crystallization, gelation, gelatinization, denaturation and oxidation during heating, cooling or freezing. All these transformations occur in a certain range of temperature and are associated with heat variations. Thermal analysis techniques, particularly DSC, are used as a primary approach for investigating these properties of foods. However, food processing involves mixtures of food constituents and not just simple systems; these may be mixed or diluted with a liquid (water, milk, oil) or with a powder (sugar, fibre). For simulation of such transformations and interactions, the limited volume and the lack of in situ mixing, constitute the major drawbacks of techniques involving DSC. Micro-calorimetry provides an ideal solution for such investigations because it has the capacity to work on bulk materials and diluted solutions with a very high sensitivity.
Principally, it uses the heat flux calorimetric principle for food characterization and the calorimeter consists of a measurement chamber surrounded by a detector (thermocouples, resistance wires, hermistors, and thermopiles) to integrate the heat flux exchanged by the sample contained in an adapted vessel. The chamber is insulated in a surrounding heat sink made of a material having high thermal conductivity. Table 3.6 provides an overview of some endothermic or exothermic effects occurring in various types of food.

Table 3.6 (Endothermic/ Exothermic) effects for different food component (Parlouër & Benoist, 2009).
Food component Endothermic effect Exothermic effect
Fat, oil Melting, lipid transition Crystaliasation, oxidation
Protein Denaturation Aggregation, crystalisation
Enzyme Denaturation Aggregation, enzymatic reaction
Starch Gelatinisation, glass transition Retrogradation, oxidation
Milk Melting Crystalisation, oxidation
Hydrocolloid, gelatin Melting Gelation
Carbohydrates Melting, glass transition Crystallisation, decomposition
Yeast – Fermentation
Bacteria – Growth, metabolism, fermentation

In this thesis the study of thermal profiles of liquid and solid systems such as gelatin and oat mixture, a micro DSC (Fig. 3.4) was utilised as it was found to be more sensitive in revealing thermal events. On the structural characteristics of the gelatin/oat mixtures, the thermal analysis provides a firm footing on the structural behaviour of the systems in a conjunction with rheological measurements. Thermal events of gelatin solution at a concentration of 2% (w/w) with oat particle inclusion (1-4% w/w) was revealed in cooling profile from 40 °C to 0 °C and heating profile up to 90 °C at the constant speed of 0.5 °C/min. Characterisation on thermal transition of lipid, starch and protein present in oat particles was examined using the above protocol.
Scanning electron microscopy (SEM)
Scanning electron microscopy (SEM) has a strong advantage because of its capability to evaluate samples ranging in size from nanometre up to the centimeter scale. The spacious chamber and goniometer of an SEM can accommodate relatively large samples as compared to the more traditional transmission electron microscopes and provide nearly unlimited points of viewing with assistance of translational, tilting and rotary movements (Rouèche, Serris, Thomas, & Périer-Camby,2006; Shu et al., 2006; Zhang et al., 2010). SEM produces an image of a sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals containing information about the characteristics of the sample, particularly surface topography, composition as well as electrical conductivity. Secondary electrons, back scattered electrons (BSE), characteristic X-rays, light (cathodoluminescence), specimen current and transmitted electrons are the different types of signals produced by an SEM.
In the most common or standard detection mode, secondary electron imaging, the SEM can produce very high-resolution images of a sample surface revealing details having a size of approximately 1 to 5 nm in size. SEM micrographs yield a characteristic three-dimensional appearance making them very useful for understanding the surface structure of a sample. A wide range of magnifications is also possible from about × 25 (equivalent to that of a powerful hand-lens) to × 250,000, corresponding to 250 times the magnification limit of the best light microscopes. The components of an SEM are shown in figure 3.5 and generally consist of a lens system, electron gun, and detector as well as visual and photo recording cathode ray tubes. The beam from the electron gun is passed through electron lenses in order to decrease spot size, thus
producing a clear image. Subsequently, the signals from the beam-specimen from different locations are collected by the electron detector. This then converts the collected signals to point–by–point intensity differences on the monitor providing an image of the sample (FEI, 2008; Kimseng & Meissel, 2001).
The specific instrument used in present study was the Philips XL30 (Figure 3.6) belonging to the RMIT Microscopy and Microanalysis Facility (RMMF). This instrument possesses mode of operation, namely high-vacuum. However, the high-vacuum mode was the most suitable choice of operation to examine the protein and polysaccharide samples such as gelatin/oat fibre mixture will be discussed in the following chapters. The Philips XL30 can collect secondary electron (topography) images using a standard chamber mounted Everhart-Thornley detector, or a backscatter detector can be mounted to the bottom of the column to collect backscatter electron images. Backscatter electron images contain atomic number contrast (Z-contrast), so can be useful for elemental identification. The Philips XL30 detectors are used for (i) chamber mounted Everhart-Thornley (ETD) which can be operated in various modes (ii) polepiece mounted BSE detector and (iii) IR camera for viewing sample/column.
In the work of this thesis, the SEM was utilised to produce tangible evidence of the phase morphology single (gelatin and oat fibre) and also gelatin/fibre mixture solutions which single gelatin content 2% (w/w) protein in the presence of varying levels of oat fibre 1%, 2%, 3% and 4% (w/w). The particle size distribution (d(v,0.9)) used in this work was 182.2 μm. The sample preparation for SEM study was used as the same method to prepare the rheology study sample (see section 3.2.1.2 in this chapter). The samples for imaging were freeze-dried at -55 oC for overnight and gold plated preparations under a high-vacuum mode. An accelerating voltage of 30 kV was used to produce microscopic images of these conductive samples, thus assisting in the characterisation of network morphology.
3. Particle size analysis by laser light scattering
The particle size distribution of UHT samples was measured by laser light scattering principle. UHT samples were analyse immediately after preparation and during the 12-weeks to rage period. Five micrometres of sample was dispersed in the sample chamber with continuous mixing and them measurements were performed in triplicates at room temperature. The instrument used for laser light scattering was a Malvern Mastersizer X (Figure 3.7) and the main features selected for this study were : analysis model (polydisperse), dispersant ( Distilled water) and distribution value option was selected
ARG-2
In this thesis, the Advanced Rheometer Generation 2 (ARG-2) by TA instruments was used to generate results from large-scale deformation for viscosity study and small-scale deformation oscillation experiments from gelatin/fibre mixtuer study . This rheometer is able to qualitatively and quantitatively measure the viscoelasticity of fluids, semi-solids and solids (under appropriate examination conditions). Keeping all parameters constant, but varying the following (one at a time): temperature, time, frequency and strain can provide valuable information about the system under examination. In chapter 7 the rheometer was performed on UHT beverages to determin a consistency of the products in term of steady shear viscosity as affected by the particle size distribution (372-35 µm) and level of fibre addition (0.5-5 % w/w in formulations) after samples were loaded on the Peltier plate at 22 ºC using 40 mm parallel-plate geometry and 1 mm gap. The changes in viscosity of the beverages were reported for fresh and extended storage over 12 weeks at two temperatures of interest (22 and 30 ºC). Furthermore, ARG-2 rheomoter was carried out a small deformation oscillatory measurements in-shear of gelatin solution and oat/gelatin mixtures as presented in chapter 6 In order to observe the gelation of gelatin matrix, a variable amount of gelatin (2-25%, w/w) was cooling to 10°C at a scan rate of 1°C/min. In the latter experiment, exact amount of gelatin concentration 2% (w/w) was a continuous phase to server as a baseline for possible changes in network morphology with a variable amount of oat (0-4%, w/w) and three different particle size distributions (28.2, 82.9, and 182.2 μm) using a series of rheological tests of time sweep (3 hrs), frequency sweep (0.1-100 rad/s) and strain sweep (0.1-100%) via using 40 mm parallel-plate geometry and 2 mm gap.

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