Fabrication, Structure and Functional Characterizations of pH-Responsive Hydrogels Derived from Phytoglycogen.

Xiuting Hu,Yimei Chen,Yao Liu,Ming Miao,Tao Zhang

doi:10.3390/foods10112653

Abstract

The pH-responsive hydrogels were obtained through successive carboxymethylation and phosphorylase elongatation of phytoglycogen and their structure and functional characterizations were investigated. Phytoglycogen (PG) was first carboxymethylated to obtain carboxymethyl phytoglycogen (CM-PG) with degree of substitution (DS) at 0.15, 0.25, 0.30, and 0.40, respectively. Iodine staining and X-ray diffraction analysis suggested that the linear glucan chains were successfully phosphorylase-elongated from the non-reducing ends at the CM-PG surface and assembled into the double helical segments, leading to formation of the hydrogel. The DS of CM-PG significantly influenced elongation of glucan chains. Specifically, fewer glucan chains were elongated for CM-PG with higher DS and the final glucan chains were shorter, resulting in lower gelation rate of chain-elongated CM-PG and lower firmness of the corresponding hydrogels. Scanning electron microscope observed that the hydrogels exhibited a porous and interconnected morphology. The swelling ratio and volume of hydrogels was low at pH 3–5 and then became larger at pH 6–8 due to electrostatic repulsion resulting from deprotonated carboxymethyl groups. Particularly, the hydrogel prepared from chain-elongated CM-PG (DS = 0.25) showed the highest sensitivity to pH. These results suggested that phosphorylase-treated CM-PG formed the pH-responsive hydrogel and that the elongation degree and the properties of hydrogels depended on the carboxymethylation degree. Thus, it was inferred that these hydrogels was a potential carrier system of bioactive substances for their targeted releasing in small intestine.

Highlights

Hydrogel is composed of hydrophilic polymers that form the three-dimensional structure through chemical or physical cross-linking, which can absorb and retain a high percentage of water or biological liquids
After PG was carboxymethylated, the λmax did not significantly change, but the intensity of the absorption peak decreased as the degree of substitution (DS) increased, which suggested that carboxymethyl groups inhibited complexation between glucan and iodine
Was 0, 0.15, 0.25, 0.30 and 0.40, respectively (Figure 1b). These results suggested that treatment by phosphorylase increased the glucan length of carboxymethyl phytoglycogen (CM-PG)

Summary

Introduction

Hydrogel is composed of hydrophilic polymers that form the three-dimensional structure through chemical or physical cross-linking, which can absorb and retain a high percentage of water or biological liquids. Chemical cross-linking usually involves the chemical reaction of complementary groups on natural or synthetic polymers [1,2]. The defects of this technique include the harsh reaction conditions and the use of toxic reagents. Intelligent hydrogels have arose the growing interest for applications in controlled release of active ingredients, which can undergo reversible volume change in response to small alterations of external environmental stimuli, such as pH, temperature, magnetic field, electric field, etc.

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