Sobanwa, Motolani
(2022)
Redesign of collagen casings for high quality performance using food grade polysaccharides.
PhD thesis, University of Nottingham.
Abstract
Collagen film (casings) obtained from acid-swollen collagen fibres is widely used as an alternative to natural casings for sausage production. However, collagen casings possess weak properties such as low mechanical properties (tensile strength and stiffness) and thermal stability compared to natural casings. Therefore, there is a need industrially to improve these properties. The main purpose of this work was to study the effects of polysaccharides on the properties of acid-swollen collagen pastes and films as a function of collagen paste concentrations (2.5 %, 3.5 % and 4 %wt/wt). In this work, polysaccharides dispersions: cellulose fibres of different length and waxy (WS) and high amylose (HAS) maize starch granules and molecular solutions: Hydroxypropylmethylcellulose (HPMC), Methylcellulose (MC), high molecular weight (GH), low molecular weight guar gum (GM) and Carboxymethylcellulose (CMC) were blended with acid-swollen collagen paste to fabricate collagen films with improved properties such as mechanical properties (tensile strength, stiffness and flexibility) and thermal stability. The viscoelastic of the blend pastes and denaturation of collagen was studied by rheological and thermal techniques. The pure and composite films were studied by sorption, mechanical, spectroscopic, structural, and thermal techniques.
The focus of the first part of this study is to investigate the effect of uncharged and negatively charged molecular solutions at comparable low-shear viscosity on the viscoelastic and thermal properties of acid-swollen collagen paste. Dynamic rheological data indicated that the addition of non-charged hydrocolloids: HPMC, MC, GH and GM increased the storage modulus (G’) and loss modulus (G’’) of the acid-swollen collagen paste. By contrast, negatively charged CMC decreased the G’ and G” of the collagen pastes. At the level of addition of non-charged solutions (HPMC, MC, GH and GM) considered in this study, the denaturation temperature of collagen as determined by DSC was not affected while negatively charged CMC increased the denaturation temperature.
Composite films containing blends of collagen paste with the individual molecular solutions were formed. Films were characterised for their mechanical, thermal, sorption and structural properties. Collagen/CMC films were not tested due to the difficulty in analysing the films. The thickness of the films increased and was dependent on the collagen concentration as well as the hydrocolloid concentration in the film network. Mechanical data revealed that the addition of hydrocolloids increased the tensile strength (TS), stiffness (YM), and elongation at break (EAB) of the films. Derivatised cellulose showed higher enhancement than the guars. Consistent with the mechanical data, DSC revealed an increase in peak temperature and a decrease in enthalpy of the films with the addition of the polymers. An increase in TS, YM, and EAB and an increase in peak temperatures were dependent on the collagen concentration. XRD data of the composite film showed a reduction in the intensity of the crystalline peak of collagen. FTIR spectra of the films helped to understand the structural changes and the interaction between the collagen and hydrocolloids. The thermal degradation temperature of collagen was not affected, as evidenced by the TGA curves. Furthermore, the composite films showed lower moisture uptake than the pure collagen films.
The next study focused on investigating the effect of polysaccharide dispersions, cellulose with different fibre length, waxy and high amylose maize starches at comparable dispersed phase volume on the rheological and thermal properties of acid-swollen collagen paste. The dynamic rheological measurement revealed the dominant elastic behaviour (G’ > G’’) of the blend and control pastes. Cellulose fibres, waxy and high amylose starch granules increased the storage and loss modulus, and values increased with increasing collagen content. The starches exhibited a higher value due to the high concentration used. According to the DSC data, the denaturation of collagen and enthalpy of melting was not affected by the addition of the dispersions. On the other hand, on reheating the blend pastes, the starches lowered the enthalpy of the denatured collagen. Films were made from the blend pastes and were characterised for their mechanical, thermal, sorption and structural properties. The surface of composite films appeared rough because of the protrusion of the cellulose fibres and starch granules. The thickness of the films increased with the addition of the cellulose fibres and starch granules. Values increased with increasing levels of collagen and dispersions concentration in the film-forming paste. Reinforcing collagen films with cellulose fibres increased the mechanical properties (TS, YM and EAB) of the films. The mechanical properties of collagen with starch granules films could not be tested due to the brittleness of the films. DSC data showed that cellulose fibres increased the peak temperature of the films. By contrast, starch granules decreased the peak temperature. The enthalpy of the films was significantly reduced with the addition of cellulose fibres and starch granules. Collagen with starch granules films had the lowest enthalpy values. XRD data showed a decrease in the intensity of the crystalline peak of collagen in the blend films. The thermal stability of collagen was reduced, as evidenced by the TGA data. Additionally, the water uptake of the films decreased with the addition of cellulose fibres and starch granules.
For the final study, the effect of collagen pastes (2.5%, 3.5% and 4 % wt) on the pasting properties of waxy (WS), high amylose (HAS) and normal (NS) maize starches were studied using Rapid Viscous Analyser (RVA) at conventional (up to 95 °C) and high-temperature (up to 140 °C) heating modes. Results showed that collagen pastes modified the pasting properties of the starches. At conventional heating mode, high amylose did not show a noticeable pasting profile. The pasting temperature of waxy starch was unaffected by the addition of collagen paste. By contrast, the addition of collagen paste lowered the pasting temperature of normal starches. The viscosities (peak, setback, and breakdown) of NS and WS increased. The final viscosity of WS decreased while that of NS increased with the increase in collagen paste concentration. When the samples are heated to temperatures 140 °C higher, HAS showed a noticeable pasting profile. The pasting temperature of HAS decreased with increasing levels of collagen paste addition. Peak and breakdown viscosities of NS, WS, and HAS increased with increasing collagen paste levels. In contrast, setback and final viscosities reduced.
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