Article

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

Department of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
Food Hydrocolloids (Impact Factor: 4.09). 07/2011; 25(5):1105-1111. 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.

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    • "The gel structure, however, can be physically enhanced by acid exposure (Norton, Cox, & Spyropoulos, 2011), or by the addition of cations (Morris, Nishinari, & Rinaudo, 2012; Nishinari, Miyoshi, Takaya, & Williams, 1996). Acid exposure influences the mechanical properties of the gellan gels, with the pH influencing the optimal concentration of gellan for gel strength(Norton et al., 2011). Addition of divalent cations cross-links the polymer chains, binding two carboxylate groups, resulting in a stabilised gellan structure (Oliveira et al., 2010; Tang, Tung, & Zeng, 1997). "
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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.
    Full-text · Article · May 2014 · Food Hydrocolloids
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    • "). On the other hand, self-structuring gellan gels can be also applied as stomach filling to reduce appetite in obesity treatment (Norton et al., 2011). In order to delay gelling before administration, sodium citrate may be added to complex free Ca 2+ ions prior to use (Miyazaki et al., 1999). "
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    ABSTRACT: Over the past few decades, microbial polysaccharides have been under intense investigation due to their advantageous physicochemical properties. A great structural diversity of these biomolecules has led to multiple applications in food industry, personal care products, pharmacy and medicine. Currently, one of the most widely studied and fully described member of this group is gellan. It is a linear polymer produced by Sphingomonas elodea. A polymer chain of gellan consists of a tetrasaccharide repeating unit of l-rhamnose, d-glucose and d-glucuronate. So far most of the studies have been focused on the application of gellan as a food ingredient. However, due to the unique structure and beneficial properties, gellan is currently described as a potent multifunctional additive for various pharmaceutical products. Specific gelling properties in different media led to the development of controlled release forms based on gellan. Various formulations have been studied including oral, ophthalmic, nasal and other. Recent reports suggest that gellan-based materials can also be used in regenerative medicine, stomatology or gene transfer technology.
    Full-text · Article · Mar 2014 · International Journal of Pharmaceutics
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    • "Initial acidification from neutral pH to pH 3.5 causes a large increase in work to fracture (Picone & Cunha, 2011). On further decrease in pH below the pK a of the glucuronate residues in gellan at approximately pH 3.4 (Haug, 1964), work to fracture decreases (Norton et al., 2011). At pH2 the gels are extremely weak and turbid, and show phase separation of polymer and solvent (Moritaka, Nishinari, Taki, & Fukaba, 1995). "
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    ABSTRACT: This study investigated the in vitro acid-induced gelation of mixed systems of two biopolymers; low acyl and high acyl gellan gum. Rheological and texture analysis showed that these mixed gels displayed textures that lay between the material properties exhibited for the low and high acyl variants. DSC analysis showed that mixtures of the low acyl and high acyl forms exhibit two separate conformational transitions at temperatures coincident with each of the individual biopolymers. Various metabolically relevant pH environments and hydrocolloid concentrations were investigated. These resulted in very different acid gelled structures, which were characterised by texture analysis. The structures of the acid gels were shown to depend upon the pH, hydrocolloid concentration and proportion of each biopolymer used during their production. A selection of these mixed gellan structures were assessed post-production in terms of their response to prolonged exposure to an acidic (pH 1), stomach-like, environment. This resulted in a significant increase in the gel strength, regardless of the biopolymer proportions. The high acyl gellan was less acid-sensitive, and subsequently no evidence of acid gelation was observed with high acyl gellan at a proportion greater than 60% of the total biopolymer. The findings presented here demonstrate that structuring as well as de-structuring of mixed gellan acid gels can be controlled in acidic environments similar to those that are present in the stomach after food consumption.
    Full-text · Article · Mar 2014 · Food Hydrocolloids
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Questions & Answers about this publication

  • Gerd Kloeck added an answer in Polymerization:
    Orally administered gellan gum forms a gel in situ when in acidic pH. What are some therapeutic applications of this type of gelling nature?

    Gellan gum is commonly used in bakery industry as viscosity imparting agent. This polymer forms a gel in acidic pH after oral administration. I want to know if this in situ gelling is used to deliver any therapeutic drug. I appreciate if anybody could help me. Thank you. 

    Gerd Kloeck

    You might find this work interesting: https://www.researchgate.net/publication/251544401_Acid_gelation_of_low_acyl_gellan_gum_relevant_to_self-structuring_in_the_human_stomach

    • [Show abstract] [Hide abstract]
      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.
      No preview · Article · Jul 2011 · Food Hydrocolloids