Elsevier

Process Biochemistry

Volume 73, October 2018, Pages 220-227
Process Biochemistry

Influences of extraction methods on physicochemical characteristics and activities of Astragalus cicer L. polysaccharides

https://doi.org/10.1016/j.procbio.2018.07.016Get rights and content

Highlights

  • Astragalus cicer L. polysaccharides (ACPs) were extracted using four methods.

  • Four methods were hot water, ultrasonic, enzyme, and enzyme-ultrasonic extraction.

  • Higher extraction yield of 13.91% was obtained with enzyme extraction method.

  • Enzyme extraction resulted in ACPs with better antioxidant capacity.

Abstract

The aim of this study was to assess the influences of extraction methods on the physicochemical characteristics and antioxidant activities of polysaccharides from Astragalus cicer L. (ACPs). Four methods were applied to ACPs extraction: hot water extraction (HW), ultrasonic-assisted extraction (UA), enzyme-assisted extraction (EA) and enzyme-ultrasonic-assisted extraction (EUA). The ACPs extracted by different techniques were correspondingly named HW-ACPs, UA-ACPs, EA-ACPs and EUA-ACPs. The results indicated that EA-ACPs had higher extraction yields (13.91%). The HPLC results showed that the monosaccharide contents of the four ACPs were significantly different. The ACPs presented antioxidant abilities in a concentration-dependent manner. The higher uronic acid content and smaller molecular weight of the EA-ACPs might contribute to the higher antioxidant activities of EA-ACPs among the four ACPs. These results indicated that enzyme-assisted technology can improve ACPs yields and obtain ACPs with higher antioxidant activities.

Introduction

In recent decades, polysaccharides have attracted attention from researchers due to their biological antioxidation, immunological regulation, antitumor and anti-inflammatory activities [[1], [2], [3]]. Extraction techniques exert significant influences on the extraction yields, physicochemical properties and bioactivities of polysaccharides. Currently, several extraction techniques are used to extract polysaccharides. When considering the extraction cost, operation convenience, environmental factors and extraction efficiency, each method has both benefits and drawbacks. Hot water extraction (HW) is an easy-to-operate and environmentally friendly extraction technology. However, HW generally has the disadvantages of long operation times, high extraction temperatures and low extraction yields. Ultrasonic-assisted extraction (UA) can enhance the extraction yield of polysaccharides through the generation of cavitation effects [4]. The release of polysaccharides from plant cells can be promoted by enzyme-assisted extraction (EA) due to the degradation of cell walls by enzymes such as cellulase, papain and pectinase [5]. Enzyme-ultrasonic-assisted extraction (EUA) has the benefits of both UA and EA. Microwave-assisted extraction (MA) is based on the direct application of electromagnetic radiation, which has the ability to absorb electromagnetic energy and transform it into heat, to a material. Compared with traditional methods, MA has many advantages because it consumes less time and solvent, provides a better extraction rate, and ultimately produces a higher substance yield. However, it requires higher equipment cost and operator skill [6]. Moreover, different extraction techniques can lead to differences in the biological activities of polysaccharides.

Astragalus L., the largest genus in the family of Leguminosae, is widely distributed throughout temperate regions in the world. Several species of Astragalus L. are considered to have potential anhidrotic, diuresis, antidote and tonic effects [7]. Certain species of Astragalus L. are also used for the treatment of nephritides, mellitus, leucocythemia and metrocarcinoma. The active ingredients of Astragalus L. include flavones, saponins, alkaloids, polysaccharides, sterols and phenols. The extraction efficiency of polysaccharides from Astragalus cicer L. (ACPs) has great effects on the utilization of this plant for food and pharmaceutical purposes.

Therefore, the aim of this study was to evaluate the effects of different methods (HW, UA, EA and EUA) on the extraction yields, physicochemical characteristics and antioxidant activities of ACPs. The physicochemical properties of ACPs were measured based on a series of indicators, including the chemical composition, solubility and Fourier transform infrared spectroscopy (FT-IR) results. The antioxidant activities of ACPs were determined based on an analysis of the free radical scavenging activities and ferric reducing power of these molecules. It is of interest to prepare ACPs with better antioxidant activities and analyze and characterize their physicochemical characteristics to provide a theoretical basis for future use of these ACPs in related fields.

Section snippets

Materials

The aerial parts of Astragalus cicer L. at anthesis were harvested at Jilin Agricultural University (Changchun, China) and dried at 50 °C. Subsequently, the dried plant materials were ground into powder (1 mm) and prepared for ACPs extraction. The chemicals cellulase, papain, pectinase, monosaccharide standards, 2,2-azino-bis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and vitamin C were purchased from Sigma (St. Louis, MO, USA).

ACPs extraction and preliminary purification

ACPs were extracted by

Chemical composition of ACPs

As shown in Table 1, the yields of the EA-ACPs (13.91%), EUA-ACPs (13.60%) and UA-ACPs (11.91%) were significantly higher than those of the HW-ACPs (8.42%) (P < 0.05), which suggested that the UA, EA, and EUA techniques could significantly improve the extraction yields of ACPs. Protein was not detected in the four ACPs. Different extraction techniques had no significant effects on the polysaccharides and moisture contents of ACPs (P >  0.05). However, the uronic acid contents of ACPs were

Conclusions

The effects of four extraction methods on the extraction yields, physicochemical characteristics and antioxidant activities of ACPs were investigated to select the optimal extraction technology. The results showed that the EA-ACPs had the highest extraction yield, smallest molecular weight and best antioxidant activities. The highest antioxidant activities of the EA-ACPs among the four ACPs might be related to their lower molecular weight and higher uronic acid content. Therefore, the

Acknowledgements

This work was supported by the National Natural Science Foundation of China (31601972); the General Financial Grant from the China Postdoctoral Science Foundation (2017M621224).

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