Study on preparation and separation of Konjac oligosaccharides

Abstract

To study the preparation and separation of Konjac oligosaccharides, Konjac Glucomannan was degraded by the combination of γ-irradiation and β-mannanase, and then the degradation product was separated by ultrafiltration. To our interest, for most of Konjac oligosaccharides obtained by this method, the molecular mass was lower than 2200 Da. In addition, the 1000 Da molecular weight cut off membrane could effectively separate the Konjac oligosaccharides. In conclusion, the combination of γ-irradiation and β-mannanase was an efficient method to obtain Konjac oligosaccharides, and the oligosaccharides of molecular mass lower than 1000 Da could be effectively separated by ultrafiltration.

Introduction

Konjac Glucomannan (KGM) is an essential polysaccharide composed of glucose and mannose in the ratio of 1:1.6 by the linkage of β-1, 4 glycoside (Jian, Zeng, Xiong, & Pang, 2011). It has been widely applied on food, biological materials and pharmaceutical industry because of the excellent properties, such as thickening, gelatin, and biological compatibility (Pang, Lin, Zhang, Tian, & Sun, 2003).

Recent researches found that its degradation products with different molecular mass have particular biological functions, such as anti-tumor (Vuksan et al., 2000), immunoregulation (Onishi et al., 2005), and cytothesis (Yeh, Lin, & Chen, 2010). These findings promote researchers to pay more attention to the research and development of Konjac degradation product (Suzuki et al., 2010). Presently, several strategies have been developed to obtain oligosaccharides by the depolymerization of Konjac Glucomannan (Courtois, 2009), such as acid degradation, enzymatic hydrolysis (Albrecht et al., 2011), oxydative degradation, and physical methods (Pang et al., 2012). In the previous researches, we found that γ-irradiation could effectively degrade Konjac Glucomannan. But the molecular mass distribution of the products was wide. Besides, the molecular weight is always higher than 400,000 Da in the safe irradiation dose (Xu, Sun, Yang, Ding, & Pang, 2007). Enzymatic hydrolysis has been widely applied in the degradation of polysaccharide because of the characteristics, safety and in room temperature (Qi, Li, & Zong, 2003). However, it is difficult to obtain plenty of oligosaccharides only by enzymatic hydrolysis.

Besides degradation method, the mainly problem limiting the wide use and research of Konjac degradation production is the method to obtain pure and narrowly distributed molecular mass oligosaccharides. So, it is significant to find a suitable method to effectively and precisely separate the degradation products. So far, column chromatography has been extensively used in the separation and purification of polysaccharides (Wu, Li, Che, Zhu, & Kang, 2012). But Column chromatography exhausts much time and elution, and the concentration of product is low.

Ultrafiltration has been widely applied on the separation of proteins, because its device is simple, and it has several advantages, such as good selectivity and low energy requirement (Guan et al., 2011, Zhang et al., 2009). In earlier stage, with the technological limit, it has not been applied in the separation of polysaccharides. However, with the development of membrane filtration technology, several researches about the application of ultrafiltration on polysaccharides have been reported (Prabhakar et al., 2011, Xing and Li, 2009).

In this experiment, we decomposed Konjac Glucomannan by the combination of γ-irradiation and β-mannanase; furthermore, the oligosaccharides were separated by ultrafiltration technology. This work will provide a new method and theoretical guide for the preparation and separation of oligosaccharides.