Evaluation of Anti-Inflammatory Activities of a Triterpene ß-Elemonic Acid in Frankincense In Vivo and In Vitro.

The purpose of this research was to extract and separate the compounds from frankincense, and then evaluate their anti-inflammatory effects. The isolated compound was a representative tetracyclic triterpenes of glycine structure according to ¹H-NMR and 13C-NMR spectra, which is ß-elemonic acid (ß-EA). We determined the content of six different localities of frankincense; the average content of ß-EA was 41.96 mg/g. The toxic effects of ß-EA administration (400, 200, 100 mg/kg) for four weeks in Kunming (KM) mice were observed. Compared with the control group, the body weight of mice, the visceral coefficients and serum indicators in the ß-EA groups showed no systematic variations. The anti-inflammatory effects of ß-EA were evaluated in LPS-induced RAW264.7 cells, xylene-induced induced ear inflammation in mice, carrageenin-induced paw edema in mice, and cotton pellet induced granuloma formation in rats. ß-EA inhibited overproduction of tumor necrosis factor-α(TNF-α), interleukin-6 (IL-6), monocyte chemotactic protein 1 (MCP-1), soluble TNF receptor 1 (sTNF R1), Eotaxin-2, Interleukin 10 (IL-10) and granulocyte colony-stimulating factor (GCSF) in the RAW264.7 cells. Intragastric administration with ß-EA (300, 200, and 100 mg/kg in mice, and 210, 140, and 70 mg/kg in rats) all produced distinct anti-inflammatory effects in vivo in a dose-dependent manner. Following treatment with ß-EA (300 mg/kg, i.g.), the NO level in mice ears and PGE2 in mice paws both decreased (p < 0.01). In conclusion, our study indicates that ß-EA could be a potential anti-inflammatory agent for the treatment of inflammatory diseases.

Baicalein inhibits acinar-to-ductal metaplasia of pancreatic acinal cell AR42J via improving the inflammatory microenvironment.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers. Recent research has demonstrated that chronic pancreatitis (CP) is associated with an increased risk of PDAC, partly due to acinar-to-ductal metaplasia (ADM). Baicalein has been shown to exert anti-inflammatory and anti-tumor effects for CP or PDAC, respectively. The aim of our study was to investigate the effect of baicalein, and the putative underlying mechanism, on inflammatory cytokines-induced ADM of rat pancreatic acinar cell line AR42J. To investigate ADM and baicalein effects in vitro, AR42J were treated with recombinant rat Tumor Necrosis Factor alpha (rTNFα) with or without baicalein for 5 days. Results showed that rTNFα-induced AR42J cells switched their phenotype from dominantly amylase-positive acinar cells to dominantly cytokeratin 19-positive ductal cells. Moreover, expression of the transcripts for TNFα or Hes-1, a Notch target, was up-regulated in these cells. Interestingly, baicalein reduced the population of ADM as well as cytokines gene expression but not Hes-1. Baicalein inhibited NF-κB activation induced by rTNFα in AR42J, but no effect on Notch 1activation. Moreover, baicalein suppressed the secretion of TNFα and Nitric Oxide (NO) in macrophages stimulated with LPS and further inhibited ADM of conditional medium-treated AR42J cells. Baicalein also suppressed the inflammatory response of LPS-activated macrophages, thereby inhibited ADM of AR42J by altering their microenvironment. Taken together, our study indicates that baicalein reduces rTNFα-induced ADM of AR42J cells by inhibiting NF-κB activation. It also sheds new light on Chinese material medica therapy of pancreatitis and thereby prevention of PDAC.

Hepcidin and iron metabolism in the pathogenesis of prostate cancer.

PURPOSE: To investigate the relationship between Hepcidin and iron metabolism, and cell proliferation, migration, and apoptosis in prostate cancer cells. METHODS: PC3 prostate cancer cells were cultured in vitro and divided into the control group, Hepcidin overexpression group, and Hepcidin low expression group. Prostate specific antigen (PSA) and soluble transferrin receptor (sTfR) levels were measured by ELISA. The levels of the Hepcidin receptor membrane transporter, Ferroportin, were determined by Western blot. The intracellular iron distribution was determined by immunofluorescence assay. The cell proliferation rate was determined by MTT assay. Cell migration was measured by wound healing assay. Apoptosis was measured by flow cytometry. RESULTS: Compared with the control group, higher PSA level (p<0.05), lower sTfR level (p<0.05), lower Ferroportin level (p<0.05), lower intracellular iron level (p<0.05), higher cell proliferation and migration rate, and lower apoptotic rate (p<0.05) were found in the Hepcidin overexpression group. The opposite results were found in the Hepcidin low expression group. CONCLUSIONS: Hepcidin is highly expressed in prostate cancer cells, and can regulate cell proliferation, migration, and apoptosis by increasing intracellular iron transportation.

ß-Glucuronidase-triggered reaction for fluorometric and colorimetric dual-mode assay based on the in situ formation of silicon nanoparticles.

BACKGROUND: ß-Glucuronidase (GUS) is considered as a promising biomarker for primary cancer. Thus, the reliable detection of GUS has great practical significance in the discovery and diagnosis of cancer. Compared with traditional organic probes, silicon nanoparticles (Si NPs) have emerged as robust optical nanomaterials due to their facile preparation, superior photobleaching resistance and excellent biocompatibility. However, most nanomaterials-based methods only output a single signal which is easily influenced by external factors in complex systems. Hence, developing nanomaterial-based multi-signal optical assays for highly sensitive GUS determination is still urgently desired. RESULTS: In this study, we developed a simple and efficient one-step method for the in situ preparation of yellow color and yellow-green fluorescent Si NPs. This was achieved by combining 3-[2-(2-aminoethylamino) ethylamino] propyl-trimethoxysilane with p-aminophenol (AP) in an aqueous solution. The obtained Si NPs showed yellow-green fluorescence at 535 nm when excited at 380 nm, while also exhibiting an absorption peak at a wavelength of 490 nm. Taking inspiration from the easy synthesis step regulated by AP, which is generated through the hydrolysis of 4-aminophenyl ß-D-glucuronide catalyzed by GUS, we constructed a direct fluorometric and colorimetric dual-mode method to measure GUS activity. The developed fluorometric and colorimetric sensing platform showed high sensitivity and accuracy with detection limits for GUS determination as low as 0.0093 and 0.081 U/L, respectively. SIGNIFICANCE: This study provides a facile dual-mode fluorometric and colorimetric approach for determination of GUS activity based on novel Si NPs for the first time. This designed sensing approach was successfully employed for the quantification of GUS in human serum samples and screening of GUS inhibitors, indicating the feasibility and potential applications in clinical cancer diagnosis and anti-cancer drug discovery.

Improving the digestive stability and prebiotic effect of carboxymethyl chitosan by grafting with gallic acid: In vitro gastrointestinal digestion and colonic fermentation evaluation.

Carboxymethyl chitosan (CMCS) is a useful polysaccharide with potential applications in food, cosmetic and biomedical industries. Nonetheless, CMCS is unfavorable for maintaining intestinal flora balance. In this study, gallic acid (GA) was grafted with CMCS through ascorbic acid/hydrogen peroxide initiated graft copolymerization reaction, producing GA grafted CMCS (GA-g-CMCS). The digestive and fermentative behavior of CMCS and GA-g-CMCS were investigated by using in vitro simulated gastrointestinal digestion and colonic fermentation models. Results showed that the average molecular weight (Mw) of CMCS gradually decreased during saliva-gastro-intestinal digestion, changing from original sheet-like morphology to porous and rod-like fragments. However, the Mw and morphology of GA-g-CMCS were almost unchanged under saliva-gastro-intestinal digestion. Meanwhile, the grafted GA moiety was not released from GA-g-CMCS during saliva-gastro-intestinal digestion. As compared with CMCS fermentation, GA-g-CMCS fermentation significantly suppressed the relative abundance of Escherichia-Shigella, Paeniclostridium, Parabacteroides, Lachnoclostridium, Clostridium_sensu_stricto_1, UBA1819 and Butyricimonas, while facilitated the relative abundance of Enterobacter, Enterococcus, Fusobacterium and Lachnospira. In addition, GA-g-CMCS fermentation significantly enhanced the production of short-chain fatty acids. These findings suggested that the digestive stability and prebiotic effect of CMCS were improved by grafting with GA.

[M cell in vitro model and its application in oral delivery of macromolecular drugs].

The oral administration of bioactive macromolecular drugs such as proteins, peptides and nucleic acids represents unprecedented challenges from the drug delivery point of view. One key consideration is how to overcome the gastrointestinal tract absorption barrier. Recent studies suggest that microfold cell (M cell), a kind of specialized antigen-sampling epithelial cell which is characterized by a high endocytic rate and low degradation ability, may play an important role in macromolecule oral absorption. The development of an in vitro M cell coculture system and its modified models greatly advanced the study of M cells and the development of oral delivery system for macromolecular drugs. The special structure, function and formation characteristics, and biomarkers of M cell are summarized in this review. The applications of in vitro M cell models in developing oral delivery system ofbioactive macromolecular drugs are discussed.

Recent advances in the preparation, structural characteristics, biological properties and applications of gallic acid grafted polysaccharides.

Natural polysaccharides are important biopolymers with unique physicochemical properties and valuable biological activities. Due to the lack of sufficient functional groups, the applications of natural polysaccharides are incomparable to synthetic biopolymers. In order to broaden the applications of polysaccharides, gallic acid (GA, one kind of phenolic acid with numerous functional properties) has been grafted onto polysaccharides through several chemical and enzymatic methods. The structural characteristics and physical properties (e.g. water solubility, thermal stability, crystalline character and viscosity) of polysaccharides are greatly changed by grafting with GA. Meanwhile, GA grafted polysaccharides (GA-g-polysaccharides) show improved biological activities (e. g. antioxidant, antimicrobial, antitumor, anti-inflammatory, anti-allergic, enzyme inhibitory, prebiotic, and calcium oxalate crystals formation inhibitory effects) and broadened applications in the fields of active packaging, edible coating, encapsulation, delivery and bioadsorption. Notably, the structural characteristics, physical properties, biological activities and applications of GA-g-polysaccharides are affected by the grafting ratio and grafting method. Herein, recent advances of GA-g-polysaccharides in terms of preparation methods, structural characteristics, biological activities and potential applications are summarized. This review will provide a guideline for the scientific community towards more rational design and targeted use of GA-g-polysaccharides in the future.

Structural characterization and protective effect of gallic acid grafted O-carboxymethyl chitosan against hydrogen peroxide-induced oxidative damage.

In this study, gallic acid (GA) was grafted onto O-carboxymethyl chitosan (O-CMCS) by a free radical-mediated method. The synthesized GA grafted CMCS (GA-g-CMCS) was characterized by several instrumental methods and the antioxidant activity of the conjugate was evaluated by in vitro and cellular assays. Results showed the grafting ratio of GA-g-CMCS was 60.8 mg GAE/g. Thin layer chromatography and UV-vis, Fourier-transform infrared and proton nuclear magnetic resonance spectroscopic analyses all confirmed GA was successfully grafted onto O-CMCS. Meanwhile, covalent linkage formed between the amino group of O-CMCS and the carboxyl group of GA via amide bond. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and the reducing power of O-CMCS were remarkably improved by grafting with GA. Cellular assays showed GA-g-CMCS was non-toxic to RAW264.7 cells at 25-400 µg/mL. Moreover, GA-g-CMCS had a protective effect against hydrogen peroxide (H2O2)-induced oxidative damage in RAW264.7 cells. As compared with H2O2-treatment alone, the pretreatment of the cells with 100, 200 and 400 µg/mL of GA-g-CMCS significantly increased cell viability, reduced apoptosis and intracellular reactive oxygen species production, and improved membrane integrity and intracellular antioxidant enzyme (superoxide dismutase, catalase, glutathione peroxidase) activity. Our results suggested GA-g-CMCS could be developed as a novel antioxidant.

Preparation and characterization of antioxidant packaging by chitosan, D-α-tocopheryl polyethylene glycol 1000 succinate and baicalein.

Baicalein (BN) is a kind of flavonoid with strong antioxidant ability. In this study, antioxidant packaging was developed by incorporating BN and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) into chitosan (CS) film matrix for the first time. Effect of BN content (0.5 wt%, 1 wt% and 2 wt% on CS basis) on the structure, physical, release and antioxidant properties of CS-TPGS-BN films was investigated. Micro-structural observation showed 0.5 wt% of BN was compatible with film matrix, whereas 1 wt% and 2 wt% of BN reduced the homogeneity of the film. Fourier transform infrared spectroscopy revealed hydrogen bonds formed between BN and film matrix. X-ray diffraction showed the crystallinity of CS-TPGS film was increased by BN incorporation. The addition of BN remarkably increased the yellowness, water vapor and light barrier properties, opacity and antioxidant activity of the film. The release of BN from CS-TPGS-BN films to fatty food stimulant was demonstrated to fit second-order, Ritger-Peppas, and first-order models. Notably, CS-TPGS-BN films could effectively inhibit the oxidation of soybean oil during 28 days of storage. Thus, CS-TPGS-BN films could be used as novel antioxidant packaging for fatty foods.

Synthesis, characterization, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate.

In this study, corn starch was functionalized with quercetin. Starch was first oxidized by sodium periodate to produce starch aldehyde, and then starch aldehyde was conjugated with quercetin through acid catalyzed condensation reaction. The structure, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate were evaluated. Thin layer chromatography confirmed the conjugate did not contain free quercetin. The UV-vis spectrum of the conjugate exhibited an absorption band at 320 nm. Fourier-transform infrared and proton nuclear magnetic resonance spectra of the conjugate confirmed the aldehyde groups of starch aldehyde were involved in the conjugation reaction. X-ray diffraction pattern revealed the conjugate was in the amorphous state. Scanning electron microscopy observation showed the conjugate had sheet-like, virgate and round shapes. The structure of starch aldehyde-quercetin conjugate was different from that of native starch and starch aldehyde. As compared with native starch and starch aldehyde, starch aldehyde-quercetin conjugate exhibited higher reducing power, free radical scavenging activity and antimicrobial activity against Escherichia coli, Staphylococcus aureus, Salmonella and Listeria monocytogenes. Our results suggested starch aldehyde-quercetin conjugate could be developed as an antioxidant and antimicrobial agent in food industry.

Acetyl-α-boswellic acid and Acetyl-ß-boswellic acid protects against caerulein-induced pancreatitis via down-regulating MAPKs in mice.

This study is to investigate the protective effect of Acetyl-α-boswellic acid and Acetyl-ß-boswellic mixture(α/ß-ABA), which is the active ingredients isolated from Frankincense, on actue pancreatitis and its mechanism. Our experimental results showed that 2 µM α/ß-ABA reduced production of NO, TNF-α, IL-6, IL-10 and IL-1ß in RAW264.7 cells that were stimulated with lipopolysaccharide (LPS) which indicates its anti-inflammatory role. In pancreatitis model induced by caerulein, intra-gastrical administration of 100 mg/kg α/ß-ABA relieved inflammatory cells infiltration significantly and attenuated the serum elevation of amylase TNF-α and IL-6 remarkably in mice. Furthermore, α/ß-ABA down-regulated mitogen-activated protein kinase (MAPK) family phosphorylated proteins in pancreas, including phosphorylated p38, ERK1/2 and JNK, to reduce the serum inflammatory factors. Finally, α/ß-ABA alleviated the pancreatic edema and inflammatory cell infiltration in pancreatitis mice model. This study suggests that α/ß-ABA may be targeted for drug development against pancreatitis via modulating MAPKs pathway.

Anti-inflammatory effects of Rhodiola rosea L.: A review.

Rhodiola rosea L., a worldwide botanical adaptogen, has been confirmed to possess protective effects of inflammatory injury for many diseases, including cardiovascular diseases, neurodegenerative diseases, diabetes, sepsis, and cancer. This paper is to review the recent clinical and experimental researches about the anti-inflammatory effects and the related mechanisms of Rhodiola rosea L. extracts, preparations, and the active compounds. From the collected information reviewed, this paper will provide the theoretical basis for its clinical application, and provide the evidences or guidance for future studies and medicinal exploitations of Rhodiola rosea L.

Preparation of pH-sensitive and antioxidant packaging films based on κ-carrageenan and mulberry polyphenolic extract.

In this study, antioxidant and pH-sensitive κ-carrageenan based films were developed by incorporating different amounts of mulberry polyphenolic extract (MPE). Due to abundant anthocyanin content, MPE showed pH-sensitive property with solution color changed from red to purple and final gray when pH value increased from 2 to 13. When MPE was incorporated into κ-carrageenan film, the composite films presented blue color. Notably, the incorporation of 2 and 4 wt% of MPE could significantly increase the thickness, tensile strength, thermal stability, antioxidant activity and pH-sensitive property of κ-carrageenan film. However, the moisture content, water vapor permeability, UV-vis light transmittance and elongation at break were greatly reduced when 2 and 4 wt% of MPE were incorporated. In addition, κ-carrageenan-MPE films exhibited heterogeneous and rougher surfaces as compared with κ-carrageenan film. The existence of intermolecular interactions between MPE and κ-carrageenan matrix was confirmed by infrared spectroscopy and X-ray diffraction. When applied to monitor the freshness of milk, κ-carrageenan-MPE films showed evident color changes as milk deteriorated after storage at 40 °C for 8 h. Our results suggested that κ-carrageenan-MPE films could be used as novel active and intelligent food packaging materials.

Antioxidant and pH-sensitive films developed by incorporating purple and black rice extracts into chitosan matrix.

Polyphenol-rich purple rice extract (PRE) or black rice extract (BRE) was incorporated into chitosan (CS) to develop antioxidant and pH-sensitive packaging films. Effect of extract content on the structural, physical and functional properties of CS-PRE and CS-BRE films was investigated. Results showed BRE had higher total phenol and anthocyanin contents than PRE. Scanning electron microscope showed that 1 wt% of PRE or BRE was compatible with film matrix, whereas 3 and 5 wt% of the extract significantly decreased the homogeneity of film matrix. Fourier transform infrared spectroscopy and X-ray diffraction further indicated that intermolecular hydrogen bonds formed between CS and the extract. Notably, the incorporation of PRE or BRE increased the thickness, light barrier property and antioxidant activity of CS film. Moreover, the water vapor barrier property and tensile strength of CS-PRE and CS-BRE films first increased and then decreased with the increase of extract content. Due to abundant anthocyanins in the extract, CS-PRE and CS-BRE films were pH-sensitive in different buffer solutions. When used to monitor pork spoilage, CS-PRE films showed more significant color changes than CS-BRE films. Our results suggested CS-PRE films could be used as antioxidant and intelligent packaging films in food industry.

Preparation and characterization of antioxidant and antimicrobial packaging films based on chitosan and proanthocyanidins.

The antioxidant and antimicrobial food packaging films were prepared by using chitosan (CS) and proanthocyanidins (PA). Effect of PA content (0, 5, 10, 15 and 20 wt% of PA on CS basis) on the physical, antioxidant and antimicrobial properties of CS-based films were determined. The prepared CS-PA films showed a brown color. PA incorporation remarkably increased the thickness, water solubility, water vapor permeability, opacity, tensile strength and thermal stability of CS film; whereas significantly reduced the moisture content, oxygen permeability, UV-vis light transmittance, elongation at break and crystallinity of CS film. Scanning electron microscopy showed PA was evenly distributed in the CS film matrix, making the films more compact. Some spontaneous agglomeration of PA was observed in the films when PA contents exceeded 5 wt%. Infrared spectra indicated the intermolecular interactions between PA and CS were through hydrogen bonds. Notably, CS-PA films exhibited improved antioxidant and antimicrobial activity in comparison with plain CS film. Our results suggested CS-PA films could be applied as active packaging materials in food industry.

Development and characterization of antioxidant active packaging and intelligent Al3+-sensing films based on carboxymethyl chitosan and quercetin.

Different amounts of quercetin were mixed with carboxymethyl chitosan (CMCS) to develop novel antioxidant active packaging and intelligent Al3+-sensing films. The physical properties, structure, antioxidant and Al3+-sensing abilities of CMCS-quercetin composite films were investigated. Results showed CMCS-quercetin composite films presented a dark yellowish color. When compared with CMCS film, CMCS-quercetin composite films containing 5 and 7.5 wt% of quercetin on CMCS basis exhibited higher thicknesses, opacity and thermal stability; however, presented lower moisture contents, UV-vis light transmittance and elongation at break. Besides, the incorporation of quercetin could not significantly change the water solubility and water vapor barrier property of CMCS film. Morphological observation showed the surface of CMCS-quercetin composite film became coarse when 7.5 wt% of quercetin was incorporated. Infrared spectra and X-ray diffraction patterns of CMCS-quercetin composite films further indicated quercetin was compatible with CMCS. Importantly, CMCS-quercetin composite films could sustainably release antioxidant ability into aqueous and fatty food stimulants. Moreover, CMCS-quercetin composite films were sensitive to Al3+. The color and UV-vis absorption patterns of CMCS-quercetin composite films were changed by the addition of Al3+. Results suggested that CMCS-quercetin composite films could be used as novel antioxidant and intelligent Al3+-sensing materials in food packaging.

Baicalein attenuates pancreatic inflammatory injury through regulating MAPK, STAT 3 and NF-κB activation.

Acute pancreatitis (AP) is a common acute abdominal disease with local or systemic inflammatory response, caused by abnormal activation of digestive enzymes. Baicalein has been shown to exert anti-inflammatory effects and to attenuate the pathological changes of AP. The aim of the research was to investigate the effects of baicalein on caerulein induced pancreatitis, and to elucidate the putative underlying mechanism. In this study, the therapeutic potential of baicalein and its mechanism were investigated in a caerulein-induced AP in vivo and in vitro model. The results indicate that baicalein treatment alleviates the caerulein-induced pathological damage in the pancreas. Baicalein decreased the expression level of pro-inflammatory cytokines and chemokines of the pancreas in caerulein treated mice and of isolated pancreatic acinar cells. Moreover, baicalein inhibited the expression of NF-κB p65 and the phosphorylation of p38 MAPK, ERK (extracellular signal-regulated kinase) as well as STAT 3, which indicates that baicalein exerts its anti-inflammatory effects via dampening the NF-κB, MAPK and STAT 3 signaling pathways. Together, this study provides experimental evidence for the clinical application of Scutellaria baicalensis Georgi or baicalein and indicates that baicalein may be a promising candidate for treatment of AP patients in the future.

Structural and physicochemical properties of chemically modified Chinese water chestnut [Eleocharis dulcis (Burm. f.) Trin. ex Hensch] starches.

Chinese water chestnut [Eleocharis dulcis (Burm.f.) Trin. ex Hensch] is a starch-rich aquatic plant widely consumed throughout the oriental countries. In this study, different chemically modified Chinese water chestnut starches including acetylated starch (AS), succinylated starch (SS) and carboxymethylated starch (CMS) were prepared. The structural and physicochemical properties of native starch and chemically modified Chinese water chestnut starches were compared for the first time. The degrees of substitution for AS, SS and CMS were 0.087, 0.575 and 0.972, respectively. Results of powder X-ray diffractometry, small-angle X-ray scattering and scanning electron microscopy indicated the crystalline regions and morphology of native starch were destroyed by chemical modification. Notably, carboxymethylation completely destroyed the original morphology of native starch and thus CMS exhibited an amorphous state. Besides, AS and SS showed significantly lower gelatinization properties than native starch. The thermal stability decreased in the order of CMS > AS > native starch > SS, whereas viscoelastic properties decreased in the order of SS > CMS > native starch > AS pastes. Notably, CMS exhibited the highest swelling power, solubility, paste clarity and resistant starch content, implying CMS might have wide applications in food industry.

Isolation, structural characterization and bioactivities of naturally occurring polysaccharide-polyphenolic conjugates from medicinal plants-A reivew.

In recent years, several medicinal plants have been demonstrated as valuable resources of naturally occurring polysaccharide-polyphenolic conjugates. For the first time, this article introduces recent advances of polysaccharide-polyphenolic conjugates isolated from different medicinal plants. The isolation, purification, structural characterization and biological activities of polysaccharide-polyphenolic conjugates are introduced in details. In general, polysaccharide-polyphenolic conjugates can be isolated by hot water or alkaline extraction followed by purification through anion exchange chromatography or gel filtration chromatography. The structures of conjugates are usually characterized by chemical composition analysis, UV-vis, Fourier-transform infrared and nuclear magnetic resonance spectroscopy. Moreover, polysaccharide-polyphenolic conjugates exhibit several biological activities including anticoagulant, antioxidant, radioprotective, anti-platelet, antitussive and bronchodilatory effects. Therefore, polysaccharide-polyphenolic conjugates isolated from medicinal plants are certain to have a bright prospect in the field of food and pharmaceutics.

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.