Elsevier

Carbohydrate Polymers

Volume 101, 30 January 2014, Pages 332-341
Carbohydrate Polymers

Enzymolysis-ultrasonic assisted extraction, chemical characteristics and bioactivities of polysaccharides from corn silk

https://doi.org/10.1016/j.carbpol.2013.09.046Get rights and content

Highlights

  • The enzymolysis-ultrasonic assisted extraction procedure improved the yield from 4.56% to 7.10% for corn silk polysaccharides (CSPS).

  • There were obvious differences on physicochemical properties between CSPS after enzymolysis-ultrasonic assisted extraction and hot water extraction.

  • CSPS showed higher antioxidant and anti-proliferation activities after enzymolysis-ultrasonic assisted extraction.

Abstract

An enzymolysis-ultrasonic assisted extraction (EUAE) procedure of corn silk polysaccharides (CSPS) was established and the physicochemical properties, antioxidant and anticancer activities of CSPS were studied. Orthogonal test and response surface methodology were applied to optimize the extraction parameters. The optimum enzymolysis and ultrasonic conditions were cellulase content of 7.5% for 150 min at 55 °C and liquid–solid ratio of 31.8 for 34.2 min at 66.3 °C, respectively. Under these conditions, the yield of CSPS increased from 4.56% to 7.10%. CSPS obtained by hot water and EUAE were composed of rhamnose, arabinose, xylose, mannose, galactose and glucose with molecular ratios of 4.17:17.33:5.59:18.65:19.11:35.14 and 8.83:15.77:7.92:12.39:11.15:43.94, respectively. Their molecular weight distributions were 10.52 × 104 and 6.88 × 104 Da, respectively. CSPS obtained by EUAE showed morphological and conformation changes and higher antioxidant and anticancer activities compared with CSPS extracted by hot water.

Introduction

Corn silk (dried cut stigmata of maize female flowers, Zea mays L.) is a well-known functional food and traditional Chinese herbal medicine. It consists of various bioactive constituents which has significant influence on human health. The bioactivities of corn silk were widely reported in the literatures, including antioxidant activities (Liu et al., 2011), anti-proliferative effects on human tumor necrosis factor (TNF)-α and lipopolysaccharide-induced cell adhesion (Habtemaram, 1998), anti-diabetic activity on hyperglycemia rats (Zhao, Yin, Yu, Liu, & Chen, 2012), diuretic activity (Velazquez, Xavier, Batistac, & de Castro-Chaves, 2005), anticoagulant activity (Choi & Choi, 2004), antifungal (Miller et al., 2003, Zeringue, 2000), anti-fatigue (Hu, Zhang, Li, Ding, & Li, 2010) and weight loss activities (Du & Xu, 2007). Corn silk had a long history of application for therapeutic remedy and it was tested non-toxic (Wang et al., 2011).

Polysaccharides are essential biomacromolecules widely exist in the plants, microorganisms, algae and animals. Some polysaccharides isolated from natural sources showed various biological activities such as antidiabetic, antitumor, immunomodulatory and anti-inflammatory effects (Huang et al., 2012, Jiang et al., 2011, Kang et al., 2011, Liang, 2008), which were strongly affected by their chemical structures and chain conformations (Yang & Zhang, 2009). Polysaccharide was one of the main components of corn silk. Previous studies showed that polysaccharides from corn silk (CSPS) could lead to weight loss (Du & Xu, 2007), regulate blood sugar (Zhao et al., 2012) and improve gastrointestinal movement (Du, Xu, & Gao, 2007). So the CSPS might be used as a novel nutraceutical agent for human consumption.

The extraction methods of polysaccharides included traditional water extraction, enzyme, ultrasonic and microwave-assisted methods, which were help to improve the extraction efficacy (Hou and Chen, 2008, Yin et al., 2011, Wang et al., 2006, Zhao et al., 2010). However, single method usually requires longer extraction time or higher temperature but lower extraction efficiency. Enzymolysis-ultrasonic assisted extraction is a combined extraction method, which is undoubtedly an emerging technology in the food industry since it owns advantages of two extraction methods such as mild extraction conditions, lower investment costs and energy requirements, and simplified manipulation.

Recently, response surface methodology (RSM) has been used increasingly to optimize processing parameters because it allows more efficient and easier arrangement and interpretation of experiments compared to other methods (Box and Behnken, 1960, Gan et al., 2010, Prakash Maran et al., 2013). Box–Behnken design (BBD) is a type of response surface design. It is an independent quadratic design in that it does not contain an embedded factorial or fractional factorial design. In this design the treatment combinations are at the midpoints of edges of the process space and at the center. These designs are rotatable (or near rotatable) and require 3 levels of each factor (Zou, Chen, Yang, & Liu, 2011). It is more efficient and easier to arrange and interpret experiments comparing with others. It was widely used in many studies on extraction of bioactive constituents (Prakash Maran et al., 2013, Yan et al., 2011, Zhao et al., 2011). Therefore, it was more efficient and easier to arrange and interpret experiments to optimize the extraction parameters for corn silk polysaccharides with an enzymolysis-ultrasonic assisted extraction (EUAE) procedure. Though there were some reports on the extraction of the corn silk polysaccharides (Prakash Maran et al., 2013, Zhao et al., 2011). There is no study on enzymolysis-ultrasonic assisted extraction with BBD on the corn silk polysaccharides till now.

In this study, the enzymolysis-ultrasonic assisted extraction, chemical characteristics and bioactivities of CSPS were investigated to obtain an effective method for CSPS with higher yield and bioactivities. Orthogonal test method with three factors and three levels was designed to optimize the process parameters of enzymolysis pretreatment. With that a three-level, three-variable BBD was used to optimize the ultrasonic extraction parameters of CSPS. Chemical structure, antioxidant and anticancer activities, and the preliminary structure-activity relationship of CSPS were discussed.

Section snippets

Materials and chemicals

Corn silk was gathered from cornfield in September 2012 in Tianjin, China. The corn silk variety was Jingke968 as authenticated by associated Professor Haixia Chen. 1,1-diphenyl-2-picrylhydrazyl (DPPH), arabinose, galactose, glucose, rhamnose and mannose were provided by Sigma Chemical Co. (St, Louis, MO, USA). Sephadex G-100 was purchased from GE Healthcare Bio-Sciences AB (Uppsala, Sweden). Cellulase (10,000 U/g) was obtained from TianJin NuoAo Enzyme Co., Ltd. All other chemicals and reagents

Enzymolysis pretreatment

The orthogonal test with three factors and three levels was designed to analyze the optimal parameters of the enzymolysis treatment. From the range analysis (Table 1), the polysaccharide yield was increased from 1.683% to 4.893%, the sequence of influential significance of the three factors was B > A > C, the optimum combination was A2B3C1, so the optimum conditions were as follows, the cellulase content was 7.5%, the enzymolysis temperature was 55 °C, the enzymolysis time was 150 min. Under these

Conclusion

An efficient enzymolysis-ultrasonic assisted extraction procedure (EUAE) was employed to extract polysaccharides from corn silk (CSPS) in this study for the first time. The orthogonal test and Box–Behnken design (BBD) were applied to optimize the process parameters of enzymolysis (cellulase content of 7.5% for 150 min at 55 °C) and ultrasonic pretreatment (liquid–solid ratio of 31.8 for 34.2 min at 66.3 °C) and a maximum CSPS yield of (7.10%) could be obtained. Furthermore, ultrasonic treatment

Acknowledgements

The authors are grateful for the financial support of this research from the National High Technology Research and Development Program (“863” Program) of China (Grant No. SS2013AA100207), the financial support of Project of National Key Technology Research and Development Program for the 12th Five-year Plan (No. 2012BAD33B08).

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