Acid gelation of low acyl gellan gum relevant to self-structuring in the human stomach

ArticleinFood Hydrocolloids 25(5):1105-1111 · July 2011with256 Reads
DOI: 10.1016/j.foodhyd.2010.10.007
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.
    • However, applicability of this polymer alone is limited by its instability at low pH which results in earlier release of the bioactive compound than expected [38] . This instability may be overcome by its complexion with anionic polysaccharide such as gellan gum which resists drug release at low pH [39,40]. Further, due to ease in scale up approaches, electrostatic complexation method is mostly considered for the commercial production of polymeric nanoparticles.
    [Show abstract] [Hide abstract] ABSTRACT: The objective of the present study was to prepare ketoconazole loaded chitosan-gellan gum (CSGG) nanoparticles and to evaluate them for antifungal activity against Aspergillus niger. Ketoconazole loaded CSGG nanoparticles were prepared by electrostatic complexation technique using chitosan (CS) as cationic polymer and gellan gum (GG) as anionic polymer with ketoconazole as drug. It was observed that the effect of gellan gum on particle size was more pronounced in comparison to chitosan and increase in its concentration resulted in a significant increase in particle size but decrease in zeta potential. Whereas, increase in concentration of chitosan resulted in increase in zeta potential. The particle size and zeta potential of optimal formulation was 155.7 ± 26.1 nm and 32.1 ± 2.8 mV which obtained at concentration of chitosan (0.02% w/v) and gellan gum (0.01% w/v). On comparative evaluation, ketoconazole loaded CSGG nanoparticles showed significantly higher antifungal activity against Aspergillus niger than dummy CSGG nanoparticles (without drug) and drug individually.
    Full-text · Article · Sep 2016 · Food Hydrocolloids
    • Acid self-structuring of anionic polysaccharides is regarded as one of the most efficient strategies to promote control of gastric structuring and retard stomach emptying leading to an enhanced satiety response (Bradbeer et al., 2014; Norton et al., 2011 ). Assessment of intragastric structuring ability of sodium alginate under physiologically simulated conditions is essential as the multivalent counterion composition complexity of saliva and gastric fluids can impact, under specific pH conditions, its ionotropic complexation performance.
    [Show abstract] [Hide abstract] ABSTRACT: In the present work, the intragastric structuring ability of o/w emulsions either stabilised (1-4%, w/w of sodium alginate (SA)) or structured with sheared ionic gel (1-3%, w/w of SA crosslinked with Ca2+) in the absence (saliva and gastric phases constituted of deionised water) or presence of in vitro pre-absorptive conditions (physiological simulated saliva and gastric fluids) was investigated. Visualisation of the morphological aspects of the gastric chymes, in the absence of multivalent counterions, demonstrated that SA stabilised systems underwent a remarkable swelling in the pH range of 2-3, whilst at the same pH range, ionic SA gel structured systems maintained their major structure configuration. When the aforementioned systems were exposed to physiological intragastric fluids, a reduction of the length and the hydrodynamic volume of the alginate fibres was detected regardless the structuring approach. On their exposure to physiological intragastric conditions (pH = 2), SA stabilised emulsions underwent sol-gel transition achieving a ca. 3- to 4-order increase of storage modulus (at 1 Hz). In the case of ionic sheared gel structured emulsions, exposure to physiological intragastric fluids resulted in a 10-fold reduction ability of their acid structuring ability, most likely due to the dialysis of egg-box dimer conformations by monovalent cations and protons and the sterical hindering of hydrogen bonding of MM and GG sequences under acidic conditions. Using of non-physiological simulated intragastric fluids was associated with overestimated structuring performance of SA regardless its physical state.
    Full-text · Article · Dec 2015
    • From the obtained true stress/true strain curves, the slope of the second linear region (strains over ~0.1), leading to the subsequent failure of the structure, were used to calculate the bulk modulus of each sample (A. B. Norton, Cox, & Spyropoulos, 2011; Nussinovitch, 2004).
    [Show abstract] [Hide abstract] ABSTRACT: Although hydrocolloids are used in a wide range of applications, understanding of microstructural interactions in the past have often based solely on mechanical properties. Systems which contain multiple polymers of similar properties are often, therefore, hard to fully understand since it is difficult to distinguish visually between the different phases. As such, the development of a novel staining method could aid our understanding of how microstructure relates to mechanical properties. This research has developed a method for the staining, and consequent visualisation, of low acyl gellan gum using 5-(4,6-dichlorotriazinyl) aminofluorescein (DTAF) without staining of a second polymer (gellan or PVA). The addition of DTAF on the gellan backbone was shown to affect mechanical properties, resulting in stronger gels. The influence of changing the ratios of DTAF stained gellan, and unstained gellan mixtures was also investigated. It was found; however, that these form phase separated networks. In conclusion, DTAF modification does enable fluorescent staining of gellan and allows the visualisation of microstructural interactions; however, since the modification influences the mechanical properties of the material, this staining method would be best employed as a validation method when used alongside other analytical techniques. (C) 2015 The Authors. Published by Elsevier Ltd.
    Full-text · Article · Apr 2015
    • e quiescent gels produced with 1% [w/w] agar and increasing concentrations of glucose and glycerol. The changes in the textural properties of the gels were assessed in terms of the strain at failure and the Young's Modulus (E) which was obtained as the slope of the initial linear region of the curve (below 0.05 strain), as described in the work of Norton et al. (2011). The addition of glucose (up to 40%) leads to stiffer agar gels, as indicated by the gradual increase in E. The strain at failure also increases, indicating that gels become more deformable (less brittle ) (Fig. 1A). Although several studies have investigated the influence of sugars on the mechanical properties of polysaccharide gels, the
    [Show abstract] [Hide abstract] ABSTRACT: The effects of glucose and glycerol on the lubrication properties of agar fluid gels have been studied using soft tribology. A novel approach using the sediment and supernatant of centrifuged fluid gels has allowed investigation of the distinct contributions of both the gelled particulate phase and the continuous phase on fluid gel tribology. The friction coefficient of both the particulate phase and fluid gels was significantly lower than that of the continuous phase across the three lubrication regimes. This indicates that particle entrainment occurs at all entrainment speeds, enhancing lubrication by prevention of surface contact.
    Full-text · Article · Mar 2015
    • However, the variation in gel strength with increasing concentration of acid is not monotonic. The addition of acid results in a large increase in break stress (Picone & Cunha, 2011) down to pH 3.5, where it then proceeds to decrease with further pH decline (Norton et al., 2011), until the gels become extremely weak and exhibit precipitation of the polymer by pH 2 (Moritaka et al., 1995). This behaviour is particularly evident inFig.
    [Show abstract] [Hide abstract] ABSTRACT: Fluid gels have shown potential for use in numerous applications including foods. One such application is in the production of self-structuring food formulations that take advantage of natural digestive processes to increase satiety, potentially helping to combat obesity. The formation and properties of low-acyl gellan gum fluid gels, produced by applying shear during the gelation process are discussed. The acid gelation process of the low-acyl gellan gum fluid gels was investigated through the direct addition of hydrochloric acid, inducing a range of pH environments and also their response to a prolonged exposure to an acidic environment, similar to the conditions found in the stomach. Quiescent LA gellan gum gels were also exposed in this way for comparison to the fluid gels.
    Full-text · Article · Jan 2015
    • The Young's modulus (E) was calculated as the slope of the initial linear region of the true stress/true strain curves as described elsewhere (Norton, Cox, & Spyropoulos, 2011).
    [Show abstract] [Hide abstract] ABSTRACT: The formation and properties of alginate fluid gels produced using in-situ calcium release and a defined shear field are investigated. Results show that, while the rate of particle growth during formation increases significantly upon lowering the shear rate, the rate of inter-particle interaction post-production remains unaffected by the magnitude of shear. The longer polymer chain allows a greater number of possible sites for calcium crosslinking per chain which enhances the formation of a percolating network and increases the number of rheologically-effective network crosslinks. As a result, high M-w alginate fluid gels exhibit faster gelation kinetics and greater viscosities than those of low M-w alginate fluid gels. Particle stiffness increases with increasing CaCO3 concentration until a critical value is reached. Quiescent gels display the same CaCO3 critical value, suggesting that the number of crosslinks within an individual fluid gel particle is equivalent to that of their counterpart quiescent gel. This is due to the fast coil-dimer transition which, under the applied shear field, leads to kinetically trapped fluid gel structures. However, their textural response differs from that of a quiescent gel which is likely caused by the bridging between fluid gel particles. In addition to advancing the understanding of the production of fluid gels from alginates, this work shows for the first time how the ordering kinetics and the resulting particle properties can be manipulated by the choice of alginate M-w and CaCO3 concentration, potentially allowing the design and delivery of specific structures with desirable attributes.
    Full-text · Article · Oct 2014
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