Elsevier

Food Chemistry

Volume 212, 1 December 2016, Pages 256-263
Food Chemistry

The textural properties and microstructure of konjac glucomannan – tungsten gels induced by DC electric fields

https://doi.org/10.1016/j.foodchem.2016.05.162Get rights and content

Highlights

  • KGM gels were induced by DC electric field in the presence of metal ions.

  • The textural properties and the morphology of KGM-T gels were emphatically investigated.

  • Our finding paves the way to use DC electric field for the design of other polysaccharide gels.

Abstract

Konjac glucomannan – tungsten (KGM-T) gels were successfully prepared under DC electric fields, in the presence of sodium tungstate. The textural properties and microstructure of the gels were investigated by Texture Analyzer, Rheometer and SEM. Based on the response surface methodology (RSM) results, the optimum conditions for KGM-T gel springiness is 0.32% sodium tungstate concentration, 0.54% KGM concentration, 24.66 V voltage and 12.37 min treatment time. Under these conditions, the maximum springiness value of KGM-T gel is 1.21 mm. Steady flow measurement indicated that KGM-T gel showed characteristic non-Newtonian pseudoplastic behaviour, with low flow behaviour indexes in the shear thinning region. SEM demonstrated the porosity of the freeze-dried samples. These findings may pave the way to use DC electric fields for the design and development of KGM gels and to apply KGM gels for practical applications.

Introduction

Hydrogels fabricated from natural polymers are biomaterials of particular interest in food science and biomedical applications, such as drug and nutrient carriers, food matrix and tissue engineering scaffolds (Luo, Teng, Wang, & Wang, 2013). One of the major factors defining the effectiveness of the applications of gels is their stability, that is closely related to the gel structure (e.g., the number of junctions and their strength) (Dranca & Vyazovkin, 2009). Due to the non-equilibrium meta-stable nature of gels, their structure depends significantly on the preparation methods. Polysaccharides, used either individually or in combination, can be used to create a variety of gel structures, acting as food matrix, fat replacer, drug delivery carrier, and have become an important food and biomedical material (Herrero et al., 2014, Rohart and Michon, 2014, Tiwari (Sharma) et al., 2015, Yamazaki et al., 2013, You et al., 2015).

Konjac glucomannan (KGM) is a natural polysaccharide derived from the tubers of Amorphophallus konjac K. Koch. It has been widely used in food, biomedical, and engineering fields, owing to its excellent gelling properties (Huang, Chu, Huang, Wu, & Tsai, 2015). Until now, there are mainly three different types of KGM gels – thermally irreversible gels prepared in presence of an alkaline coagulant (Du et al., 2012, Luo et al., 2013a), thermally irreversible gels with boron (Gao et al., 2008, Jian et al., 2011, Ratcliffe et al., 2013), and synergistic gels prepared with gums, such as xanthan and carrageenan (Brenner et al., 2015, Fan et al., 2008, Sun et al., 2009). The use of electric fields to induce the assembly of biopolymers has been utilized in the field of biomaterials, where the goal has been to design and control material structure for various biomedical applications (Kojic et al., 2012). One of the applications has involved the formation of silk-protein hydrogels (Kojic et al., 2012, Leisk et al., 2010, Yucel et al., 2010, Lu et al., 2011). Silk fibroin drug-loaded electrogel system provides a promising way to load proteins and gene medicines with a negative charge (Huang, Lu, Li, Zhang, & Zhu, 2011).

Recently the rheological properties of KGM-tungsten gels induced by DC electric field have been reported (Wang, Jiang, Lin, Pang, & Liu, 2016). Rheological studies have investigated the effect of KGM and ion concentration, voltage, and processing time on characteristic rheological properties obtained from the frequency dependence of relaxation spectra. The textural properties are also one of the important criteria to evaluate the gel performance. So, in this paper, the textural properties of the gel and how to obtain the optimum preparation conditions by means of texture profile analysis (TPA) and rheometer were studied. Finally, the microstructure was characterized by SEM.

Section snippets

Preparation of konjac glucomannan gel under DC electric fields

KGM powder with 91.4% glucomannan content, purchased from San Ai Konjac Food Co. (Zhaotong City, China), was precisely weighed and dispersed in distilled water at room temperature to prepare KGM sol of a certain concentration under magnetic stirring for 1 h, and the sols were stored overnight at 4 °C to ensure complete particle hydration, swelling and dispersion. Then, a certain amount of KCL, CaCl2, MgCl2, FeCl3 or Na2WO4·2H2O was added into the sol. The electrodes were inserted into the mixture

Preparation of KGM gels under DC electric fields

When an electric current was applied to a certain volume of 0.5% KGM sol, it was noticed that bubbles were produced on the electrodes, this is due to the production of H+ and OH during water electrolysis, releasing hydrogen and oxygen gases at the respective electrodes. These ions diffuse under DC electric field, resulting in pH variations (Kojic et al., 2012), whereby the solution around positive electrode becomes acidic and the negative electrode basic. The gel formation did not occur even

Conclusion

In this study, a series of different species of metal ions have been used to explore the possibility of KGM gel formation under DC electric field. Ultimately, KGM-Ca, KGM-Mg, KGM-Fe and KGM-T gels were successfully obtained. Four factors affecting textural properties of KGM-T gels were discussed in detail, including sodium tungstate concentration, KGM concentration, voltage, and electric treatment time, which all have significant influence on the gel textural properties. The preparation

Conflict of interest

No conflict of interest exits in the submission of this manuscript, and the manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed.

Acknowledgments

This study was supported by Post-Doctoral Science Foundation of China (2014M561864), the China Moe111 Project (B16029), the National Natural Science Funds (31279817, 31471704), and Doctoral Program of Minnan Normal University.

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