Acid gelation of low acyl gellan gum relevant to self-structuring in the human stomach
ABSTRACT The aim of this study was to investigate the in vitro acid-induced gelation of low acyl gellan gum. Various metabolically relevant pH environments and hydrocolloid concentrations were investigated. These resulted in very different acid structures, which were characterised by texture analysis, with Young’s and bulk moduli and work of failure being reported. The structures of the acid gels were shown to depend upon the pH and hydrocolloid concentration (c) used during their production, with a maximum in gel strength between pH 3 and 4. Both the Young’s and bulk moduli data suggest that there is a critical concentration for gelation to occur, and both parameter values displayed a gradual increase (which appears to be lower than a c2 dependency) as the gellan concentration was increased.Finally, these acid structures were also assessed post-production in terms of their response to prolonged exposure to an acidic (pH 1), stomach-like, environment. Exposure to the acid bath showed that the gel structure remains unaffected if it was originally produced at pH 3, but showed an increase in strength for those gels produced at pH 4 and pH 5 and a decrease for the gels initially produced at pH 2. Overall the findings presented here are promising as they clearly demonstrate that structuring as well as de-structuring of gellan acid gels can be controlled at acidic environments similar to those that are present in the stomach during and post-meal consumption.
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ABSTRACT: The aim of this research was to control the mechanical properties of gellan through the addition of a secondary polymer network, for use as an alternative to current tissue regeneration techniques. Cartilage and skin are complex structures, and a complex structure would therefore be required in order to closely mimic their mechanical properties. In this research, the gellan gels were strengthened through the addition of Poly (vinyl alcohol) (PVA), as the secondary polymer. Compressive strength and compressive stiffness were both increased with the addition on PVA, until 10-15% (w/w). This research has shown that gellan and PVA are phase separated, and the decrease on mechanical strength and stiffness is strongly affected by the polymer overlap concentration, occurring at 14% (w/w). (C) 2014 The Authors. Published by Elsevier Ltd.Food Hydrocolloids 05/2014; 42. DOI:10.1016/j.foodhyd.2014.05.001 · 4.28 Impact Factor
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ABSTRACT: Stress relaxation behaviour of high acyl gellan gels has been investigated, and data were fitted successfully by a seven elements empirical model and a four term modified Maxwell model with three fixed relaxation times (20, 200 and 2000 s). In addition, the effect of testing parameters on stress relaxation characteristics and the relationship between those characteristics and intrinsic gel properties were studied. High acyl gellan gels were tested in stress relaxation with different cross‐head speeds (0.1–10 mm s−1) to applied strains (3–30%). The results showed that the cross‐head speed had little effect on stress relaxation behaviour of gels. With increasing the applied strain, the initial stress and the equilibrium stress increased. The equilibrium stresses from relaxation measurement were positively related to the hardness from TPA tests (R 2 = 0.991). Relaxation appeared to be associated with the shifting of cross‐links in the gel matrix.International Journal of Food Science & Technology 12/2013; 48(12). DOI:10.1111/ijfs.12251 · 1.35 Impact Factor
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ABSTRACT: Gellan microgels with potential application in delivery systems were obtained by physically cross-linked gellan gum. The microgels were produced by atomization followed by ionotropic gelation using CaCl2 (gellan/Ca) or KCl (gellan/K) as hardening agent and part of them were coated with chitosan in order to improve their resistance to gastric digestion. Size distribution, morphology and zeta potential of microgels were evaluated before and after in vitro digestion process. The long term stability was also evaluated. Spherical microparticles were obtained at gellan concentration above 0.6% w/w, showing average size among 70–120 μm. Most of the coated and uncoated microgels showed stability in aqueous media, except the uncoated gellan/K microgel. The in vitro digestion evaluation showed that all particles maintained their size and shape after the gastric digestion step. However, the enteric digestion caused disintegration of microgels indicating their potential application for enteric delivery systems. The chitosan-coated microgels showed lower degree of fragmentation when compared to the uncoated microgels, indicating that the coating process enable a better control of microgels releasing properties during the enteric digestion.Carbohydrate Polymers 03/2015; 117:54–62. DOI:10.1016/j.carbpol.2014.09.019 · 3.92 Impact Factor