Isolation and structure characterization of a low methyl-esterified pectin from the tuber of Dioscorea opposita Thunb

Prospects of yam (Dioscorea) polysaccharides: Structural features, bioactivities and applications

Yam (Dioscorea) is a tuber crop cultivated for food security, revenue, and medicinal purposes. It has been used to treat diabetes, asthma, diarrhea, and other diseases. The main active ingredients in yam, polysaccharides, are regarded to be the important reason for its widespread applications. Now, a comprehensive review of research developments of yam polysaccharides (YPs) was presented to explore their prospects. We outlined the structural characteristics, biological activities, structure-activity relationships, and potential applications. Around 13 neutral components and 17 acidic components were separated. They exhibited various bioactivities, including immunomodulatory, hypoglycemic, hypolipidemic, antioxidant, gastrointestinal protective, anti-fatigue, and senile disease treatment activities, as well as prebiotic effect. Structure-activity relationships illustrated that unique structural properties, chemical modifications, and carried biopolymers could influence the bioactivities of YPs. The potential applications in medicine, food, and other fields have also been summarized.

Structural elucidation a complex galactosyl and glucosyl-rich pectin from the pericarp of immature fruits of Juglans mandshurica Maxim

A glucosyl-rich pectin, JMMP-3 (Mw, 2.572 × 104 g/mol, O-methyl % = 3.62%), was isolated and purified from the pericarp of the immature fruit of Juglans mandshurica Maxim. (QingLongYi). The structure of JMMP-3 was studied systematically by infrared spectroscopy, monosaccharide compositions, methylation analysis, partial acid hydrolysis, and 1/2D-NMR. The backbone of JMMP-3 possessed a smooth region (→ 4GalA1 →) and a hairy region (→ 4GalA1 → 2Rha1 →) with a molar ratio of 2: 5. The substitution of four characteristic side chains (R1-R4) occurs at C-4 of → 2,4)-α-Rhap-(1→, where R1 is composed of → 5)-α-Araf-(1→, R2 is composed of → 4)-β-Galp-(1 → and β-Galp-(1→, R3 is composed of α-Glcp-(1→, →4)-α-Glcp-(1 → and → 4,6)-α-Glcp-(1→, and R4 is composed of → 5)-α-Araf-(1→, β-Galp-(1→, → 4)-β-Galp-(1→, → 3,4)-β-Galp-(1→, → 4,6)-β-Galp-(1 → and → 2,4)-β-Galp-(1 → . In addition, the antitumor activity of JMMP-3 on HepG2 cells was preliminarily investigated.

Structural and functional characteristics of pectins from three cultivars of apple (Malus pumila Mill.) pomaces

This study aimed to investigate the chemical composition, structural properties, and biological properties of pectin polysaccharides (AP-FS, AP-QG, and AP-HG) isolated from different varieties of apple pomace. Based on the methylation and nuclear magnetic resonance analyses, the structure of AP-FS was determined to be composed of an α-1,4-linked homogalacturonan backbone that exhibited high levels of O-6 methylation. All pectins exhibit potent inhibitory activity against human colon cancer and human liver cancer cells, along with immunostimulatory effects. Among them, AP-FS exhibited the highest activity level. Finally, we further investigated the underlying mechanism behind the effect of AP-FS on RAW 264.7 cells using proteomics analysis. Our findings revealed that AP-FS triggers RAW 264.7 macrophage activation via NOD-like receptor (NLR), NF-κB, and mitogen-activated protein kinase (MAPK) signaling pathways. Therefore, our research contributes to a better understanding of the structure-function relationship among apple pectins, and AP-FS has the potential to be applied to dietary supplements targeting immunomodulation.

Structural characterization and prebiotic activity of rhamnogalacturonan-I rich pumpkin pectic polysaccharide extracted by alkaline solution

The present study aimed to investigate the structural and physicochemical characteristics of alkali-extracted pectic polysaccharide (AkPP) and to evaluate its prebiotic effects. AkPP was obtained from pumpkin pulp using an alkaline extraction method. AkPP, which had a molecular weight (Mw) of mainly 13.67 kDa and an esterification degree of 9.60%, was composed mainly of galacturonic acid (GalA), rhamnose (Rha), galactose, and arabinose. The ratio of the homogalacturonan (HG) region to the rhamnogalacturonan-I (RG-I) region in AkPP was 48.74:43.62. In the nuclear magnetic resonance spectrum, the signals indicating α-1,4-linked D-GalA, α-1,2-linked L-Rha, α-1,2,4-linked L-Rha residues were well resolved, demonstrating the presence of the HG and RG-I regions in its molecular structure. Collectively, AkPP was low methoxyl pectin rich in the RG-I region with short side chains and had a low Mw. Thermal analysis revealed that AkPP had good thermal stability. Compared to inulin, AkPP more effectively promoted the proliferation of Lactobacillus acidophilus, Lacticaseibacillus rhamnosus GG, Lacticaseibacillus casei, and Lacticaseibacillus paracasei and the production of lactic, acetic, and propionic acids. This study presents the unique structural features of AkPP and provides a scientific basis for further investigation of the potential of AkPP as a promising prebiotic.

Physicochemical Characterization, Antioxidant and Anticancer Activity Evaluation of an Acidic Polysaccharide from Alpinia officinarum Hance

AHP-3a, a triple-helix acidic polysaccharide isolated from Alpinia officinarum Hance, was evaluated for its anticancer and antioxidant activities. The physicochemical properties and structure of AHP-3a were investigated through gel permeation chromatography, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. The weight-average molecular weight of AHP-3a was 484 kDa, with the molar percentages of GalA, Gal, Ara, Xyl, Rha, Glc, GlcA, and Fuc being 35.4%, 21.4%, 16.9%, 11.8%, 8.9%, 3.1%, 2.0%, and 0.5%, respectively. Based on the results of the monosaccharide composition analysis, methylation analysis, and NMR spectroscopy, the main chain of AHP-3a was presumed to consist of (1→4)-α-D-GalpA and (1→2)-α-L-Rhap residues, which is a pectic polysaccharide with homogalacturonan (HG) and rhamnogalacturonan-I (RG-I) structural domains containing side chains. In addition, the results of the antioxidant activity assay revealed that the ability of AHP-3a to scavenge DPPH, ABTS, and OH free radicals increased with an increase in its concentration. Moreover, according to the results from the EdU, wound healing, and Transwell assays, AHP-3a can control the proliferation, migration, and invasion of HepG2 and Huh7 hepatocellular carcinoma cells without causing any damage to healthy cells. Thus, AHP-3a may be a natural antioxidant and anticancer component.

Structural and flow rheological properties of pumpkin pectic polysaccharide extracted by citric acid

The present study aimed to investigate the structural and physicochemical characteristics of acid-extracted pumpkin pectic polysaccharide (AcPP) and to evaluate their flow rheological properties. AcPP was extracted from pumpkin pulp using the citric acid extraction method. The physicochemical and structural properties were analyzed by chemical methods and instrumental analyses. The obtained results showed that AcPP consisted predominantly of GalA (85.99 %) and small amounts of Rha, Gal, and Ara, with the ratio of HG/RG-I being 81.39/16.75. In addition, AcPP had medium DE (45.34 %) and contained four macromolecular populations with different Mw of 106.03 (main), 10.15, 4.99, and 2.90 kDa. The NMR analysis further confirmed that AcPP contained a linear backbone consisting of α-1,4-linked GalA residues, some of which were partially methyl-esterified. Furthermore, AcPP was amorphous in nature and had favorable thermal stability. The effects of extrinsic factors on the flow rheological properties of AcPP were evaluated. In particular, the high concentrations of CaCl2 (8 mM) and MgCl2 (10 mM) were effective in enhancing the viscosity and non-Newtonian shear-thinning behavior of the AcPP solution. This study elucidates the unique molecular structure of AcPP and suggests the potential of AcPP as a rheology modifier in low-viscous and mineral-reinforced beverages.

Degradation of Angelica sinensis polysaccharide: Structures and protective activities against ethanol-induced acute liver injury

Angelica sinensis polysaccharide (ASP) possesses diverse bioactivities; however, its metabolic fate following oral administration remains poorly understood. To intuitively determine its intestinal digestion behavior after oral administration, ASP was labeled with fluorescein, and it was found to accumulate and be degraded in the cecum and colon. Therefore, we investigated the in vitro enzymatic degradation behavior and identified the products. The results showed that ASP could be degraded into fragments with molecular weights similar to those of the fragments observed in vivo. Structural characterization revealed that ASP is a highly branched acid heteropolysaccharide with AG type II domains, and its backbone is predominantly composed of 1,3-Galp, →3,6)-Galp-(1→6)-Galp-(1→, 1,4-Manp, 1,4-Rhap, 1,3-Glcp, 1,2,3,4-Galp, 1,3,4,6-Galp, 1,3,4-GalAp and 1,4-GlcAp, with branches of Araf, Glcp and Galp. In addition, the high molecular weight enzymatic degradation products (ASP H) maintained a backbone structure almost identical to that of ASP, but exhibited only partial branch changes. Then, the results of ethanol-induced acute liver injury experiments revealed that ASP and ASP H reduced the expression of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and malondialdehyde (MDA) and increased the superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) levels, thereby relieving ethanol-induced acute liver injury.

Research progress on the structure, derivatives, pharmacological activity, and drug carrier capacity of Chinese yam polysaccharides: A review

Chinese yam is a traditional Chinese medicine that has a long history of medicinal and edible usage in China and is widely utilised in food, medicine, animal husbandry, and other industries. Chinese yam polysaccharides (CYPs) are among the main active components of Chinese yam. In recent decades, CYPs have received considerable attention because of their remarkable biological activities, such as immunomodulatory, antitumour, hypoglycaemic, hypolipidaemic, antioxidative, anti-inflammatory, and bacteriostatic effects. The structure and chemical alterations of polysaccharides are the main factors affecting their biological activities. CYPs are potential drug carriers owing to their excellent biodegradability and biocompatibility. There is a considerable amount of research on CYPs; however, a systematic summary is lacking. This review summarises the structural characteristics, derivative synthesis, biological activities, and their usage as drug carriers, providing a basis for future research, development, and application of CYPs.

Mechanism of feed moisture levels in extrusion treatment to improve the instant properties of Chinese yam (Dioscorea opposita Thunb.) flour

Extruded yam flour was prepared at different feed moisture to improve its instant properties. The water solubility index (WSI) and water absorption index (WAI) were used to compare the instant properties of yam flour. Their chemical compositions, particle size distribution, crystalline structure, and microscopic forms were also analyzed to assess the effects of feed moisture on the instant properties of yam flour. We found that extrusion significantly improved the instant properties of yam flour, while the WSI value increased from 29.50% to 71.86% and the WAI value decreased from 387.88% to 228.06% with decreased feed moisture. Extrusion led to the degradation of total starch and amylopectin, and the contents of soluble substances increased markedly. Extrusion destroyed the granular and crystalline structures, which were reconstituted as amylose-lipid complexes with a significant decrease in relative crystallinity. Increasing the feed moisture was beneficial to the flow and color retention, while lower feed moisture was more favorable to enhance the instant properties.

Extraction of pectins from renewable grapefruit (Citrus paradisi) peels using deep eutectic solvents and analysis of their structural and physicochemical properties

This study presents an innovative attempt to extract high-quality pectins from grapefruit (Citrus paradisi) peels by using deep eutectic solvents (DESs) as extraction agents. The maximum yield of betaine-citric acid (BC)-extracted pectin (BC-P) reached 36.47 % under the optimum process conditions: an L/S ratio of 25 mL/g, a pH of 2.0, and a temperature of 85 °C for 120 min. The yield of BC-P was significantly higher than HCl-extracted pectin (HCl-P, 8.76 %) under a pH of 2.0. In addition, the structural, physicochemical, and emulsifying properties of the purified pectins (BC-P and HCl-P) and commercial pectin (CP) were comparatively analyzed. Results showed that BC-P exhibited higher RG-I value, more arabinan side-chains, bigger Mw and Mn value than HCl-P. Moreover, the viscosity, G' and G'' of BC-P were significantly higher than those of HCl-P and CP. More importantly, BC-P demonstrated better emulsifying activity and stability compared to HCl-P and CP. When the concentration of BC-P was increased to 1.50 %, a stable emulsion containing a 50 % soybean oil fraction could be obtained. Our results confirmed that DESs can be considered as high-effective agents for pectin extraction. Pectins extracted from grapefruit peels can be as a promising natural emulsifiers that can be used in the food industry.

Characterization, in vitro digestibility, antioxidant activity and intestinal peristalsis in zebrafish of Dioscorea opposita polysaccharides

The soluble crude polysaccharides from Dioscorea opposita (DOP1 and DOP2) were prepared and characterized. DOP1 and DOP2 obtained carbohydrate (65.71% and 70.18%, respectively), uronic acid (63.71% and 24.84%, respectively) and protein (8.09% and 9.51%, respectively) with molecular weight of 49.24 kDa and 21.62 kDa, respectively. DOP samples were mainly composed of mannose, glucose, galacturonic acid, galactose, and glucuronic acid. The digestibility in vitro, antioxidant activity and intestinal peristalsis effect were then investigated. DOP1 and DOP2 were degraded with decreased molecular weights (39.58 kDa and 18.56 kDa respectively), increased reducing sugar contents (from 16.95% to 19.27%; 12.45% to 15.50% respectively) and free monosaccharides (from 0.89% to 1.42%; 0.90% to 1.14% respectively) after gastric digestion. Both DOP1 and DOP2 were resistant to intestinal digestion, suggesting that DOP samples can be considered as a dietary fiber. Additionally, DOP1 and DOP2 exhibited antioxidant activities positively correlated with the concentration and remained the activities after gastrointestinal digestion in vitro. Furthermore, DOP reduced the fluorescence intensity significantly, indicating DOP can promote the intestinal peristalsis of zebrafish larvae (5 pdf) at 500 μg/mL. Therefore, DOP1 and DOP2 have a better functionality as dietary fibers, including antioxidant activity and intestinal peristalsis promotion, which can be developed as functional foods.

Structural characterization and anti-oxidation activity of pectic polysaccharides from Swertia mileensis

In this study, we isolated the pectic polysaccharide WSMP-A2b (37 kDa) from the stems and leaves of Swertia mileensis, and we investigated its compositional/structural features and antioxidant activity. FT-IR, NMR, monosaccharide composition, enzymatic hydrolysis and methylation analyses indicated that WSMP-A2b is composed of rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II) and homogalacturonan (HG) domains with mass ratios of 2.1:1.0:2.2. The RG-I domain is primarily substituted with α-L-1,5-arabinan and type II arabinogalactan (AG-II) side chains, as well as minor contributions of β-D-1,4-galactan and/or type I arabinogalactan (AG-I) side chains. The HG domain was released in the form of un-esterified and partly methyl-esterified and/or acetyl-esterified oligogalacturonides with a 1 to 7 degree of polymerization after endo-polygalacturonase degradation. WSMP-A2b showed stronger antioxidant activity in vitro, in part this might due to the presence of galacturonic acid (GalA). In addition, WSMP-A2b exerted a protective effect on tert-butyl hydroperoxide (tBHP)-induced oxidative stress in INS-1 cells by reducing reactive oxygen species (ROS) production and increasing the glutathione/oxidized glutathione (GSH/GSSG) ratio. Our results provide crucial structural information on this pectic polysaccharide from Swertia mileensis, thus prompting further investigation into its structure-activity relationship.

Impact of Sulfur Fumigation on the Chemistry of Dioscoreae Rhizoma (Chinese Yam)

Dioscoreae Rhizoma (Chinese yam; derived from the rhizome of Dioscorea opposita Thunb.) (DR), commonly consumed as a food or supplement, is often sulfur-fumigated during post-harvest handling, but it remains largely unknown if and how sulfur fumigation impacts the chemistry of DR. In this study, we report the impact of sulfur fumigation on the chemical profile of DR and then the molecular and cellular mechanisms potentially involved in the chemical variations induced by sulfur fumigation. The results show that sulfur fumigation significantly and specifically changed the small metabolites (molecular weight lower than 1000 Da) and polysaccharides of DR at both qualitative and quantitative levels. Multifaceted molecular and cellular mechanisms involving chemical transformations (e.g., acidic hydrolysis, sulfonation, and esterification) and histological damage were found to be responsible for the chemical variations in sulfur-fumigated DR (S-DR). The research outcomes provide a chemical basis for further comprehensive and in-depth safety and functional evaluations of sulfur-fumigated DR.

Comparison of structures and emulsifying properties between water-extracted pectins from Fructus aurantii

The structural characteristics of two water-extracted pectic polysaccharides from Fructus aurantii were investigated, and the impacts of their structures on the emulsifying stability were evaluated. FWP-60 (extracted by cold water and followed 60 % ethanol precipitation) and FHWP-50 (extracted by hot water and followed 50 % ethanol precipitation) were both high methyl-esterified pectins, which were composed of homogalacturonan (HG) and highly branched rhamnogalacturonan I (RG-I) regions. The weight-average molecular weight, methyl-esterification degree (DM) and HG/RG-I ratio of FWP-60 were 1200 kDa, 66.39 % and 4.45, respectively, which were 781 kDa, 79.10 % and 1.95 for FHWP-50. The methylation and NMR analysis of FWP-60 and FHWP-50 demonstrated that the main backbone consisted of different molar ratios of →4)-α-GalpA-(1 → and →4)-α-GalpA-6-O-methyl-(1→, and the side chains contained arabinan and galactan. Moreover, the emulsifying properties of FWP-60 and FHWP-50 were discussed. Compared with FHWP-50, FWP-60 had better emulsion stability. Overall, pectin had a linear HG domain and a small number of RG-I domain with short side chains to facilitate the stabilization of emulsions in Fructus aurantii. A comprehensive knowledge of the structure characteristic and emulsifying property would enable us to provide more information and theoretical guidance for the structure and emulsion preparation of Fructus aurantii pectic polysaccharides.

Preparation and physicochemical properties characterization of hesperetin-grafted pectin conjugate

Different ratios of hesperetin (HT) were successfully grafted onto pectin from basic water (PB) molecules via free radical-induced reaction. The structure of PB-HT conjugates was characterized by ultraviolet spectroscopy, infrared spectroscopy, X-ray diffraction and scanning electron microscopy. Results indicated that HT was successfully grafted onto pectin molecules, and PB-HT-0.5 showed the highest HT content (103.18 ± 2.76 mg/g). Thermogravimetric analysis indicated that HT crystals showed good thermal resistance and could improve the thermal stability of PB-HT conjugates. Additionally, PB-HT conjugates showed good cytocompatibility and blood compatibility. This study provides a novel and efficient method to synthesize hesperetin-grafted pectin conjugate, which showed potential application in the fields of functional foods in the future.

Structural characterization and anti-lipotoxicity effects of a pectin from okra (Abelmoschus esculentus (L.) Moench)

Okra (Abelmoschus esculentus (L.) Moench) is rich in various bioactive ingredients and used as a medicinal plant in traditional medicine. In the present study, to find the polysaccharide with anti-lipotoxicity effects from okra and clarify its structure, a pectin OP-1 was purified from okra, which had a backbone containing →4)-α-GalpA-(1 → residues, and 1,5-Ara linked the main chain through the O-3 of the residue →3,4)-α-GalpA-(1→, and the C-6 of residue 1, 4-α-GalpA replaced by methyl ester. In vitro experiments showed that OP-1 pretreatment alleviated oleic acid (OA)-induced lipid accumulation, ROS generation, apoptosis, transaminase leakage, and inflammatory cytokine secretion in HepG2 cells, resulting in reduced lipotoxicity. Further molecular results revealed that OP-1 increased Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) phosphorylation and affected the expression of AMPK downstream targets, including inhibit SREBP1c and FAS, as well as activate CPT-1A. Impressively, AMPK inhibitor dorsomorphin (Compound C) blocked the effects of OP-1 against lipotoxicity. The effects of OP-1 on lipid metabolism were also diminished by dorsomorphin. Our results demonstrated that OP-1 possesses a potent function in preventing lipotoxicity via regulating AMPK-mediated lipid metabolism and provide a novel insight into the future utilization of okra polysaccharide.

Naturally and chemically acetylated polysaccharides: Structural characteristics, synthesis, activities, and applications in the delivery system: A review

Acetylated polysaccharides refer to polysaccharides containing acetyl groups on sugar units. In the past, the acetylation modification of wall polysaccharides has been a hot research topic for scientists. However, in recent years, many studies have reported that acetylation-modified plant, animal, and microbial polysaccharide show great potential in delivery systems. From the latest perspective, this review systematically presents the different sources of naturally acetylated polysaccharides, the regularity of their modification, the chemical preparation of acetylation modifications, the biological activities and functions of acetylated polysaccharides, and the application in the delivery system. In nature, acetylated polysaccharides are extensively distributed in plants, microorganism, and animals. The level of acetylation modification, the distribution of chains, and the locations of acetylation modification sites differ between species. An increasing number of acetylated polysaccharides were prepared in the aqueous medium, which is safe, environment friendly, and low-cost. In addition to being necessary for plant growth and development, acetylated polysaccharides have immunomodulatory, antioxidant, and anticancer properties. The above-mentioned multiple sources, multifunctional and multi-active acetylated polysaccharides, make them an increasingly important part of delivery systems. We conclude by discussing the future directions for research and development and the potential uses for acetylated polysaccharides.

Comparative study on physicochemical characteristics, α-glucosidase inhibitory effect, and hypoglycemic activity of pectins from normal and Huanglongbing-infected navel orange peels

This study aimed at comparing the physicochemical characteristics, α-glucosidase inhibitory effect, and hypoglycemic activity of pectins (N-NOP and H-NOP) from peels of normal and Huanglongbing (HLB)-infected Navel oranges. Results indicated the pectins were high methoxy pectins mainly composed of homogalacturonan and rhamnogalacturonan-I. The pectins exhibited similar functional groups, surface morphology, and particle size, and had no triple-helical conformation in solution. They exerted fat and glucose absorption capacities and were mixed-type noncompetitive α-glucosidase inhibitors with IC₅₀ values of 1.182 and 2.524 mg/ml, respectively. Both N-NOP and H-NOP showed hypoglycemic activity in alloxan-induced diabetic mice. Administration of them could promote the synthesis of hepatic glycogen and/or serum insulin to lower blood glucose levels and enhance antioxidant status to alleviate oxidative stress injury in diabetic mice. Moreover, N-NOP had higher yield, molecular weight, ζ-potential, oil holding capacity, α-glucosidase inhibitory effect and in vivo hypoglycemic activity, whereas H-NOP possessed higher uronic acid, degree of esterification, thermal stability, water holding capacity, swelling capacity, and fat absorption capacity. It could be concluded that some similarities and differences existed between N-NOP and H-NOP in physicochemical characteristics, functional properties, α-glucosidase inhibitory effects, and hypoglycemic activity. This study provides references for the basic research and application of pectins from peels of normal and HLB-infected Navel oranges. PRACTICAL APPLICATIONS: Pectin has been widely used in the food and pharmaceutical industries for several decades due to its health benefit, gelling, thickening, and emulsification performances. Diabetes mellitus is a worldwide concern in recent years. Pectins (N-NOP and H-NOP) from peels of normal and Huanglongbing (HLB)-infected Navel oranges possessed in vitro and in vivo hypoglycemic activities, indicating they were potential anti-antidiabetic substitutes of chemical drugs. Moreover, comparative understanding on the physicochemical characteristic, α-glucosidase inhibitory effect and hypoglycemic activity of pectins from peels of normal and Huanglongbing-infected Navel oranges was conducive to the recycling and utilization of Navel orange peels. Recently, the biological activity of pectin from peels of normal Navel oranges has been rarely reported, and the information on pectin from peels of Huanglongbing-infected Navel orange is rare. This study provides references for the basic research and application of pectins from peels of normal and HLB-infected Navel oranges.

Chain conformations and steady-shear viscosity properties of pectic polysaccharides from apple and tomato

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Apple pectin was a high-ester polysaccharide, and tomato pectin was a low-ester one.

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The weight-average molecular weight (M_w) of AP was about 243 kDa, and that of TP was about 19 kDa.

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Two pectins presented semi-rigid chain conformation in aqueous solution.

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Elucidated the mechanism about shear thickening of two pectins.

In this study, apple pectin (AP) and tomato pectin (TP) were demonstrated to be a high-ester (74.8%) polysaccharide with the weight-average molecular weight (M_w) of ∼ 243 kDa and a low-ester (45.9%) polysaccharide with the M_w of ∼ 19 kDa, respectively. The semi-rigid chain conformations of pectic polysaccharides in NaNO₃ aqueous solution were deduced according to the Smidsrød “B values” of AP (0.025) and TP (0.029), while AP and TP exhibited higher stiffness in water due to the electric repulsion of carboxyl groups, which was visually observed by AFM images. Under steady shear, the shear-thickening behaviors of AP and TP in NaNO₃ aqueous solutions were observed in the shear rate range of < 1 s⁻¹, which were attributed to the disruption of the ordered arrangement induced by semi-rigid pectin chains into randomly entangled structure by weak shear force. AP exhibited stronger shear-thickening behavior due to the formation of more entanglements resulted from the higher M_w and longer side chains highly branched at rhamngalacturonan region. This study provides the scientific basis for the construction of the relationship of steady-shear property with chain conformation and molecular weight of pectin.

Structural Characterization of a Low Molecular Weight HG-Type Pectin From Gougunao Green Tea

Tea is a popular beverage with a long history of safe and healthy use. Tea polysaccharide is a bioactive component extracted from tea, which has attracted more and more attention in recent decades. In this article, an acidic polysaccharide Gougunao tea polysaccharide (GPS) was isolated from Gougunao green tea by hot water extraction and ethanol precipitation. After purification by a diethylaminoethyl (DEAE) Sepharose Fast Flow column and a Sephacryl S-400 column, several homogalacturonan (HG) and rhamnogalacturonan-I (RG-I) fractions were obtained. Fraction GPS2b with the highest yield was selected for structural characterization by methylation and nuclear magnetic resonance (NMR) analysis. GPS2b was found to be an HG-type pectic polysaccharide (degree of methyl esterification [DE], 51.6%) with low molecular weight (Mw, 36.8 kDa). It was mainly composed of →4)-α-GalpA- (1→ and →4)-α-GalpA-6-OMe-(1→. In addition, a minor highly branched RG-I domain was identified in this fraction. The investigation of structural features of tea polysaccharides can provide insights to understand their structure-bioactivity relationship.

Structural characteristics of three pectins isolated from white kidney bean

Three water-soluble pectic polysaccharides (WKBP-P2, P3 and P4) were isolated from white kidney bean by ion exchange combined with size-exclusion methods. The structural features were characterized by GC-MS, NMR spectroscopy and HPSEC-MALLS-RI. It was found that three pectic polysaccharides were the major water-extracted polysaccharides in white kidney bean. All the WKBP-P2, P3 and P4 were probably composed of various structural regions including homogalacturonan (HG), xylogalacturonan (XGA), rhamnogalacturonan I (RG-I) regions in backbone, and arabinan region mainly as side chain. However, these pectic polysaccharides were significantly different in molar ratios of these structural regions and molecular size. WKBP-P2 was HG-predominant pectin (partially methyl-esterified) with weight-average molecular weight (M_w) of 1.2 × 10⁴ g/mol, and contained minor RG-I, arabinan and probable XGA regions. WKBP-P3 (M_w of 4.0 × 10⁴ g/mol) primarily embraced XGA, HG, arabinan regions and minor RG-I region. WKBP-4 with highest M_w (4.5 × 10⁵ g/mol) had the most arabinan region (51.3%), which was probably the side chain linked to the backbone composed of RG-I, HG and slight XGA regions. These findings provided a structural basis for study on polysaccharides from white kidney bean, which was benefit for development of functional food.