Degradation of sulfated polysaccharides from Enteromorpha prolifera and their antioxidant activities
Highlights
► Degradation effect on Mw of Enteromorpha prolifera polysaccharide is investigated. ► Microwave-assistance highly accelerates degradation rate. ► Polysaccharides with low Mws are obtained by microwave-assistance acid hydrolysis. ► Degradation hardly breaks significant structural units of sulfated polysaccharide. ► Antioxidant activities of sulfated polysaccharides with different Mws are investigated.
Introduction
Recent years green algae belonging to Ulvae (including Ulva and Enteromprpha species) had been frequently involved in algal proliferation in China's Qingdao coastal areas and amounts of them were identified Enteromorpha prolifera (Muell.) J. Agardh. High quantity of algae wrack accumulating along shorelines and on the beaches produced smelly odors and arose technological issues concerning, for example, the collection and storage of this algal material. Therefore, it is urgent to find how to achieve better resource use to protect environment and reduce processing cost. It has been reported many bioactive materials in Enteromorpha species are considered to be nutritious and low-calorie food (Lahaye & Jegou, 1993). In Asia, Enteromprpha species has been used as pharmaceutical product and healthcare food for millennia.
Polysaccharides from Enteromorpha species are a group of sulfated heteropolysaccharides and their unique chemical and physicochemical properties make this family of polysaccharides attractive candidates for novel functional and biologically active polymers (Lahaye & Robic, 2007). Many researches proved sulfate polysaccharides from green algae possessed potential antioxidant activities and various classes of them had been shown as potent antioxidants. Costa reported that the sulfate polysaccharides from Codium isthmocladum (Chlorophyta) showed antioxidant activity (Costa et al., 2010). Zhang illustrated that all sulfated polysaccharides from three green algae Ulva pertusa, Enteromorpha lina and Bryopsis plumose possessed antioxidant activities in certain assays (Zhang et al., 2010). The studies on antioxidant activities of bioactive compounds from E. prolifera mainly focused on polyphenols and flavonoids in it (Ahn et al., 2012, Cho et al., 2011) while few works were reported on polysaccharides.
Furthermore, some reports indicated that molecular weights (Mws) of polysaccharide from marine algae had great influence on their antioxidant activities. Hou illustrated fucoidans with low Mws had better hydroxyl radical scavenging activities, reducing powers and superoxide radical scavenging activities (Hou, Wang, Jin, Zhang, & Zhang, 2011). Qi reported that sulfated polysaccharides with low Mws from U. pertusa Kjellm had stronger antioxidant activities (Qi et al., 2005). In order to obtain polysaccharides with low Mws, several chemical and physical methods were used including enzymatic methods, acid hydrolysis and oxidative degradation. Aarstad used enzyme engineering to produce different alginate sequences (Aarstad, Tondervik, Sletta, & Skjak-Braek, 2012). Enzymes were highly specific for cleaving glycosidic bonds in the polysaccharide chain but they were still not available for commercial preparation and utilization. Anastyuk obtained oligosaccharide fragments with low Mws from Costaria costata by mild acid hydrolysis (Anastyuk, Imbs, Shevchenko, Dmitrenok, & Zvyagintseva, 2012). Zhao prepared porphyran with different Mws from Porhyra haitanensis by ascorbate and H2O2 in combination (Zhao et al., 2006). Among acid hydrolysis and H2O2 degradation method, higher concentration or longer reaction time would be unavoidable to obtain products with low Mws, which would violently change structures of sugar units and break necessary bioactivity groups (Qin, Du, & Xiao, 2002).
As an unconventional energy source, microwave irradiation has received a great attention mainly due to considerable saving processing time, improving reaction efficiency and increasing yield of product. Microwave-assistance technology has been successfully applied in biologically active compounds extraction and synthesis, while there are few studies on degradation of polysaccharides from marine algae with microwave-assistance. Yu acquired two sulfated polysaccharides with Mw 151.6 and 28.2 KDa from U. pertusa by using a microwave degradation oven (Yu et al., 2003). Sun prepared polysaccharides with different Mws (from 2918 to 256.2, 60.66 and 6.55 kDa) from Porphyridium cruentum with microwave irradiation (Sun, Wang, Shi, & Ma, 2009). However, there are no reports about degradation of sulfated polysaccharides from E. prolifera with microwave-assistance.
In this study, the effects of degradation with microwave-assistance on Mws of polysaccharides from E. prolifera were investigated. A dedicated multimode microwave reactor was employed to precisely control reaction temperature and time. Six representative sulfated polysaccharides with different Mws were prepared and their monosaccharide compositions, sulfated contents and uronic acids were characterized. Finally the relationship between Mws and antioxidant activities of polysaccharides were investigated.
Section snippets
Materials and equipments
E. prolifera was collected on the Number One Bathing Beach of Qingdao, China 2011. The algae was washed with tap water, air dried, ground into powder and kept in plastic bags at room temperature before being used.
Nitro blue terazolium (NBT), phenazine methosulfates (PMS), nicotinamide adenine dinucleotide-reduced (NADH), hydrogen peroxide (H2O2), ferrozine, trichloroacetic acid (TCA) and standard sugars (glucuronic acid, ribose, fucose, mannose, galactose, glucose, rhamnose and xylose) were
Influence of degradation on the Mws of polysaccharides
The effects of reaction temperature, concentration of HCl, with microwave irradiation or conventional heating were studied. Samples were taken at interval during the reaction.
Fig. 1A illustrates the influence of different reaction temperatures on the Mws of degraded IEP. 60 °C, 70 °C, 80 °C, and 90 °C were cautiously selected for testing under reaction system of 1 M HCl with microwave irradiation 600 W over 60 min. The degradation rate sustained low level at comparatively low temperature. The Mws
Conclusion
This study established an efficient degradation method of E. prolifera polysaccharide with microwave-assistance acid hydrolysis method. Microwave-assistance highly accelerated the reaction rate. Polysaccharides with different Mws could be obtained by strictly controlling reaction condition. Representative polysaccharides with different Mws (Mw 446.5, 247.0, 76.1, 19.0, 5.0 and 3.1 KDa) were prepared and the relationship between Mws and antioxidant activities of polysaccharides was firstly
Acknowledgements
The study was supported by the National High Technology Research and Development Program (“863” Program) of China (2011AA09070405), and the commonweal item of State Oceanic Administration People's Republic of China (201105028-03).
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