Effects of ascorbate and hydroxyl radical degradations on the structural, physicochemical, antioxidant and film forming properties of chitosan.

In this study, chitosan (CS) was degraded by ascorbate radical (Asc•-) and hydroxyl radical (•OH), respectively. The structural, physicochemical, antioxidant and film forming properties of Asc•- and •OH degraded CS were compared for the first time. Results showed the structure and physicochemical property of Asc•- degraded CS were significantly different from those of CS. Asc•- had a deamination effect on CS with the formation of several unsaturated bonds. Accordingly, Asc•- degraded CS showed decreased crystallinity and thermal stability as well as a planar morphology. By contrast, OH degraded CS showed similar structure, crystallinity and thermal stability to CS. However, OH had an erosion effect on CS with the formation of many cavities inside. Antioxidant assay further demonstrated that the in vitro antioxidant activity of CS was improved by Asc•- and OH degradations. Moreover, film forming property of CS was also altered by Asc•- and OH degradations. Asc•- and OH degraded CS films showed higher thicknesses, UV-vis light barrier property and water vapor permeability than CS film. Besides, Asc•- degraded CS film had better mechanical properties than CS and OH degraded CS films. Therefore, Asc•- degradation could be a useful approach to improve the antioxidant and film forming properties of CS.

Reaction Mechanisms and Structural and Physicochemical Properties of Caffeic Acid Grafted Chitosan Synthesized in Ascorbic Acid and Hydroxyl Peroxide Redox System.

The ascorbic acid (AA) and hydroxyl peroxide (H2O2) redox pair induced free radical grafting reaction is a promising approach to conjugate phenolic groups with chitosan (CS). In order to reveal the exact mechanisms of the AA/H2O2 redox pair induced grafting reaction, free radicals generated in the AA/H2O2 redox system were compared with hydroxyl radical (•OH) produced in the Fe2+/H2O2 redox system. Moreover, the structural and physicochemical properties of caffeic acid grafted CS (CA-g-CS) synthesized in these two redox systems were compared. Results showed that only ascorbate radical (Asc•-) was produced in the AA/H2O2 system. The reaction between Asc•- and CS produced novel carbon-centered radicals, whereas no new free radicals were detected when •OH reacted with CS. Thin layer chromatography, UV-vis, Fourier transform infrared, and nuclear magnetic resonance spectroscopic analyses all confirmed that CA was successfully grafted onto CS through Asc•-. However, CA could be hardly grafted onto CS via •OH. CA-g-CS synthesized through Asc•- exhibited lower thermal stability and crystallinity than the reaction product obtained through •OH. For the first time, our results demonstrated that the synthesis of CA-g-CS in the AA/H2O2 redox system was mediated by Asc•- rather than •OH.

Synthesis, characterization, bioactivity and potential application of phenolic acid grafted chitosan: A review.

In recent years, increasing attention has been paid to the grafting of phenolic acid onto chitosan in order to enhance the bioactivity and widen the application of chitosan. Here, we present a comprehensive overview on the recent advances of phenolic acid grafted chitosan (phenolic acid-g-chitosan) in many aspects, including the synthetic method, structural characterization, biological activity, physicochemical property and potential application. In general, four kinds of techniques including carbodiimide based coupling, enzyme catalyzed grafting, free radical mediated grafting and electrochemical methods are frequently used for the synthesis of phenolic acid-g-chitosan. The structural characterization of phenolic acid-g-chitosan can be determined by several instrumental methods. The physicochemical properties of chitosan are greatly altered after grafting. As compared with chitosan, phenolic acid-g-chitosan exhibits enhanced antioxidant, antimicrobial, antitumor, anti-allergic, anti-inflammatory, anti-diabetic and acetylcholinesterase inhibitory activities. Notably, phenolic acid-g-chitosan shows potential applications in many fields as coating agent, packing material, encapsulation agent and bioadsorbent.

Recent advances in endophytic exopolysaccharides: Production, structural characterization, physiological role and biological activity.

Endophytes are microorganisms that colonize living, internal tissues of plants without causing any immediate, overt negative effects. In recent years, both endophytic bacteria and fungi have been demonstrated to be excellent exopolysaccharides (EPS) producers. This review focuses on the recent advances in EPS produced by endophytes, including its production, isolation and purification, structural characterization, physiological role and biological activity. In general, EPS production is influenced by media components and cultivation conditions. The structures of purified EPS range from linear homopolysaccharides to highly branched heteropolysaccharides. These structurally novel EPS not only play important roles in plant-endophyte interactions; but also exhibit several biological functions, such as antioxidant, antitumor, anti-inflammatory, anti-allergic and prebiotic activities. In order to utilize endophytic EPS on an industrial scale, both yield and productivity enhancement strategies are required at several levels. Besides, the exact mechanisms on the physiological roles and biological functions of EPS should be elucidated in future.

Extraction, characterization and in vitro antioxidant activity of polysaccharides from black soybean.

Optimization of extraction conditions, preliminary characterization and in vitro antioxidant activity of polysaccharides from black soybean (BSPS) were investigated. The results of Box-Behnken design showed that the optimal extraction conditions for BSPS were as follows: ratio of water to material of 20 ml/g, extraction time of 6.4h and extraction temperature of 92 °C, with a corresponding yield of 2.56%. The crude BSPS were further fractionated on DEAE-52 and Sepharose CL-4B chromatography to afford three purified fractions (BSPS-1, BSPS-2 and BSPS-3). Chemical analysis showed that the three purified fractions were mainly composed of carbohydrate and uronic acid. In addition, BSPS-1 was composed of arabinose, rhamnose, galactose, glucose and mannose in the molar ratio of 1.79:1.00:2.59:26.54:1.01. BSPS-2 was composed of arabinose, rhamnose, xylose, galactose and mannose in the molar ratio of 8.10:4.80:9.15:13.38:1.00. BSPS-3 was composed of arabinose, rhamnose, galactose and mannose in the molar ratio of 16.80:3.60:33.66:1.00. The results of Fourier transform-infrared spectroscopy further confirmed the characteristic polysaccharide structures of the three purified fractions. Moreover, antioxidant assays showed crude BSPS and its purified fractions had potential superoxide anion and DPPH radical scavenging activities, and their antioxidant activity decreased in the order of crude BSPS > BSPS-3 > BSPS-2 > BSPS-1.