What is dietary fiber?

Dietary fiber consists of the remnants of the edible plant cell, polysaccharides, lignin, and associated substances resistant to digestion (hydrolysis) by human alimentary enzymes. This physiological definition has been translated into a chemical method (AOAC Method 985.29), which has recently been shown to miss substances of 10, 11, and 12 degrees of polymerization. It also fails to precipitate some hydrolysis-resistant oligosaccharides which contain many physiological properties expected in dietary fiber, such as inulin and oligofructose, indigestible dextrin (Fibersol-2), galactooligosaccharides and the synthetic polymer polydextrose. The Executive Board of the American Association of Cereal Chemists has appointed a committee to explore the possibility of expanding the definition or chemical methodology for dietary fiber to accommodate components that are not hydrolyzed by human alimentary enzymes, yet have the physiological attributes normally associated with dietary fiber. However, the present review suggests that the current definition is sufficient, along with new methodology, to detect recently discovered components of the dietary fiber complex.     

膳食纤维降血脂作用及其机制的研究进展

综述了近年膳食纤维降脂作用及其机制的研究进展.膳食纤维能使血清中胆固醇、甘油三酯、低密度脂蛋白水平降低,高密度脂蛋白水平升高.其主要机制为通过减少膳食中胆固醇的吸收、影响机体中胆固醇的代谢、促进胆固醇的排泄等降低血浆中胆固醇水平;通过增加食物在肠道内的过渡时间、延缓胃排空、减缓或降低脂肪的吸收等机制降低血浆中甘油三酯水...     

Soluble Dietary Fiber,One of the Most Important Nutrients for the Gut Microbiota

Dietary fiber is a widely recognized nutrient for human health. Previous studies proved that dietary fiber has significant implications for gastrointestinal health by regulating the gut microbiota. Moreover, mechanistic research showed that the physiological functions of different dietary fibers depend to a great extent on their physicochemical characteristics, one of which is solubility. Compared with insoluble dietary fiber, soluble dietary fiber can be easily accessed and metabolized by fiber-degrading microorganisms in the intestine and produce a series of beneficial and functional metabolites. In this review, we outlined the structures, characteristics, and physiological functions of soluble dietary fibers as important nutrients. We particularly focused on the effects of soluble dietary fiber on human health via regulating the gut microbiota and reviewed their effects on dietary and clinical interventions.     

Inulin and oligofructose are part of the dietary fiber complex

Dietary fiber has been defined as the remnants of plant cells resistant to hydrolysis by human alimentary enzymes. Its main chemical constituents are hemicelluloses, celluloses, lignin, pectins, gums, and waxes. The U.S. Food and Drug Administration and the U.S. Department of Agriculture determine compliance with nutritional labeling regulations for dietary fiber by use of the existing AOAC INTERNATIONAL methods for total dietary fiber. The above compounds are readily detected by these methods. However, some oligo- and polysaccharides are resistant to human alimentary enzymes and do not precipitate in 78% ethanol, the usual reagent for precipitating dietary fiber in analytical procedures. Some of these saccharides, termed fructans, are inulin and oligofructose. They possess many physiological attributes normally associated with dietary fiber. Inulin is a mixture of oligo- and polysaccharides composed of fructose moieties joined by beta(2-->1) linkages in linear chains. Almost each chain ends with a glucose moiety. Oligofructose is a synonym for fructo-oligosaccharides, with fructose moieties joined by beta(2-->1) linkages, as in inulin. Not all molecules have a glucose unit, and the chain length is less than 10 units. A method for inulin and oligofructose was developed and approved official first action by AOAC INTERNATIONAL in early 1997. It involves extraction of sample and treatment of the extract with amyloglucosidase followed by fructozyme (Fructozyme Enzyme Process Division, Novo Nordisk, Novo Industry, Copenhagen, Denmark). The sugars released in each of the 3 steps are measured by anion-exchange chromatography. The concentration of fructans is calculated as the difference of sugars, glucose and fructose, after the enzymatic treatments and the initial sample. The repeatability standard deviations for inulin and oligofructose ranged from 2.9 to 5.8% and the reproducibility standard deviations ranged from 4.7 to 11.1%. The method was accepted by AOAC INTERNATIONAL.     

Determination of insoluble, soluble, and total dietary fiber (CODEX definition) by enzymatic-gravimetric method and liquid chromatography: collaborative study

A method for the determination of insoluble (IDF), soluble (SDF), and total dietary fiber (TDF), as defined by the CODEX Alimentarius, was validated in foods. Based upon the principles of AOAC Official Methods 985.29, 991.43, 2001.03, and 2002.02, the method quantitates water-insoluble and water-soluble dietary fiber. This method extends the capabilities of the previously adopted AOAC Official Method 2009.01, Total Dietary Fiber in Foods, Enzymatic-Gravimetric-Liquid Chromatographic Method, applicable to plant material, foods, and food ingredients consistent with CODEX Definition 2009, including naturally occurring, isolated, modified, and synthetic polymers meeting that definition. The method was evaluated through an AOAC/AACC collaborative study. Twenty-two laboratories participated, with 19 laboratories returning valid assay data for 16 test portions (eight blind duplicates) consisting of samples with a range of traditional dietary fiber, resistant starch, and nondigestible oligosaccharides. The dietary fiber content of the eight test pairs ranged from 10.45 to 29.90%. Digestion of samples under the conditions of AOAC 2002.02 followed by the isolation, fractionation, and gravimetric procedures of AOAC 985.29 (and its extensions 991.42 and 993.19) and 991.43 results in quantitation of IDF and soluble dietary fiber that precipitates (SDFP). The filtrate from the quantitation of water-alcohol-insoluble dietary fiber is concentrated, deionized, concentrated again, and analyzed by LC to determine the SDF that remains soluble (SDFS), i.e., all dietary fiber polymers of degree of polymerization = 3 and higher, consisting primarily, but not exclusively, of oligosaccharides. SDF is calculated as the sum of SDFP and SDFS. TDF is calculated as the sum of IDF and SDF. The within-laboratory variability, repeatability SD (Sr), for IDF ranged from 0.13 to 0.71, and the between-laboratory variability, reproducibility SD (SR), for IDF ranged from 0.42 to 2.24. The within-laboratory variability Sr for SDF ranged from 0.28 to 1.03, and the between-laboratory variability SR for SDF ranged from 0.85 to 1.66. The within-laboratory variability Sr for TDF ranged from 0.47 to 1.41, and the between-laboratory variability SR for TDF ranged from 0.95 to 3.14. This is comparable to other official and approved dietary fiber methods, and the method is recommended for adoption as Official First Action.     

11B solid-state NMR investigation of the rhamnogalacturonan II-borate complex in plant cell walls.

The boron in plant cell walls, which is water-insoluble and in the solid state, is solubilized by pectinase digestion to give a dimeric rhamnogalacturonan II-borate (dRG-II-B) complex. To clarify the nondestructive structure of boron present in plant cell walls (as represented by sugar beet fiber), we performed 192- and 96-MHz 11B solid state NMR measurements. The use of a high field magnet frequency of 192-MHz enabled us to observe 11B isotropic chemical shifts at -9.7 and -9.6 ppm for dRG-II-B and sugar beet fiber in the solid state, respectively, demonstrating that the boron in isolated dRG-II-B and in plant cell walls is present as a borate-diol ester (1:2). The observation of the magnetic field dependence of the chemical shift and lineshape for the borate-diol ester (1:2) by quadrupolar interaction suggested that the borate complex had a distorted tetrahedral boron structure.     

人类第七大营养素——膳食纤维

膳食纤维被称为人类第七大营养素,本文介绍了膳食纤维的有关化学问题,如其结构特点、理化性质、生理功能和检测方法,以及膳食纤维的应用与开发现状。     

Effect of Continuous and Discontinuous Microwave-Assisted Heating on Starch-Derived Dietary Fiber Production

Dietary fiber can be obtained by dextrinization, which occurs while heating starch in the presence of acids. During dextrinization, depolymerization, transglycosylation, and repolymerization occur, leading to structural changes responsible for increasing resistance to starch enzymatic digestion. The conventional dextrinization time can be decreased by using microwave-assisted heating. The main objective of this study was to obtain dietary fiber from acidified potato starch using continuous and discontinuous microwave-assisted heating and to investigate the structure and physicochemical properties of the resulting dextrins. Dextrins were characterized by water solubility, dextrose equivalent, and color parameters (L* a* b*). Total dietary fiber content was measured according to the AOAC 2009.01 method. Structural and morphological changes were determined by means of SEM, XRD, DSC, and GC-MS analyses. Microwave-assisted dextrinization of potato starch led to light yellow to brownish products with increased solubility in water and diminished crystallinity and gelatinization enthalpy. Dextrinization products contained glycosidic linkages and branched residues not present in native starch, indicative of its conversion into dietary fiber. Thus, microwave-assisted heating can induce structural changes in potato starch, originating products with a high level of dietary fiber content.     

Characterizing wood polymers in the primary cell wall of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> (L.) Karst.) using dynamic FT-IR spectroscopy

Dynamic Fourier Transform Infra-Red (FT-IR) spectroscopy was used to examine the interactions among cellulose, xyloglucan, pectin, protein and lignin in the outer fibre wall layers of spruce wood tracheids. Knowledge regarding these interactions is fundamental for understanding the fibre separation in a mechanical pulping process. Sheets made from an enriched primary cell wall material were used for studying the viscoelastic response of the polymers. The results indicated that strong interactions exist among lignin, protein, pectin, xyloglucan and cellulose in the primary cell wall. This signified a closely linked network structure of the components on the fibre surface. This ultrastructural arrangement in the primary cell wall and the relatively high content of lignin, pectin and protein in it, means that the primary cell wall is more submissive to selective chemical attacks, when compared to the secondary cell wall. A low ratio of cellulose Iα to cellulose Iβ in the primary cell wall was also found.     

Functional diversity of rhamnogalacturonans I

Rhamnogalacturonans I represent a group of plant cell wall polysaccharides having the most complex organization and variable structure. These polymers, combined in one group due to the presence of a backbone composed of alternating [→4)-α-d-GalpA-(1→2)-α-l-Rhap(1→] dimers, can occur in the cell wall both as parts of a pectin complex and by themselves. Types of rhamnogalacturonans I are unique not only for each plant but also for different tissues of the same plants and, in some cases, for different stages of development of the same tissue. Perception of the causes and consequences of this diversity is a sophisticated problem of plant glycobiology. The review summarizes the available information on the correlation of structure, physicochemical properties, and functions of rhamnogalacturonans I.     

Microfibrillated cellulose and new nanocomposite materials: a review

Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.     

Comparison of the properties of chemical cellulose pulps

The literature related to differences between chemical cellulose pulps produced by different pulping processes has been reviewed. Kraft pulps tend to be stronger, particularly in tear strength, while sulfite pulps hydrate and beat more readily. Organosolv pulps tend to mirror the properties of sulfite more than those of kraft pulps. A number of theories have been offered to explain the different properties of the chemical pulps; however, none has been universally accepted. It may be that acidic processes develop weak points in the fibers which are magnified in tear strength losses since, at a constant tensile strength, a 10% loss in fiber strength can lead to a 25–30% loss in tear strength. The effects of acidic pulping may also be magnified in greater fiber breakage and damage in the subsequent refining stages. However, strength improvements for inferior pulps can be realized through post-chemical treatments. Caustic treatments appear to give the greatest improvements, presumably due to increases in acidic group content which results in enhanced swelling properties, and possible subtle reorientation of cell wall polymers. The strength of hornified, recycled fibers can also be enhanced with such treatments, although simple beating will restore considerable strength, but at the expense of drainage rates. It is clear that the processes are complex and involve both the chemistry and physics of the fibers and how these attributes combine to affect the subsequent beating of the fibers for bonding and strength development.     

Architecture of intracellular networks in plant matrices

Pectin is an integral component of plant cell walls. It is believed to form an interconnected network structure independent of the cellulose–xyloglucan network structure. Pectin gels are often used as a model for the pectin network structure within the plant cell wall. The middle lamella pectin can be extracted with chelating agents and is believed to be associated through cooperative binding of calcium ions in the so-called egg-box junction zones. Although a great deal is known about the nature of the junction zones in pectin gels, less is known about the long-range structure within calcium-set gels. Two plausible alternative models for long-range order in these gels are a pseudo rubber-like structure and a fibrous network structure. Atomic force microscopy studies of calcium-induced gel precursors, and fragments released from gels, suggest that association leads to a branched fibrous structure within the gels. Enzymatic de-esterification of high methoxy pectin in the presence of calcium ions can induce gelation of the pectin. Thus pectin gel networks may provide a model for a self-assembled network structure within the middle lamella region of the plant cell wall.     

Cellulose-Nanocomposites: Towards High Performance Composite Materials

Summary: Strong cellulose fibres, e.g. flax and hemp, are increasingly used for composites. Despite substantial advantages, the tensile strength of these fibres is limited due to their complex structure and the unavoidable imperfections of the cell wall, inherent from growth or induced by processing. Essential improvements are possible by using highly crystalline cellulose fibrils (“whiskers”) which can be isolated from the cell wall, thus eliminating the influence of adhesion and defects. Instead of complete fibrillation, which demands special time consuming processing, a partly fibrillation has been achieved by adapted textile finishing procedures which have the potential for mass production. By combining chemical and mechanical/hydro-mechanical treatments it is possible to produce finest fibrils with diameters from below 1 µm down to the nanometer range. The problem of fibril agglomeration during drying has been avoided by forming homogenous fibrous sheets in a wet-laid non-woven process. These sheets can be impregnated with thermosetting resins. Alternatively thermoplastic polymers can be directly integrated to form hybrid materials ready for moulding. The resulting composites show greatly enhanced mechanical properties.     

Cell Wall Composition of Hemp Shiv Determined by Physical and Chemical Approaches

The use of agricultural by-products in the building engineering realm has led to an increase in insulation characteristics of biobased materials and a decrease in environmental impact. The understanding of cell wall structure is possible by the study of interactions of chemical compounds, themselves determined by common techniques like Van Soest (VS). In this study, a global method is investigated to characterise the cell wall of hemp shiv. The cell wall molecules were, at first, isolated by fractionation of biomass and then analysed by physical and chemical analysis (Thermal Gravimetric Analysis, Elementary Analysis, Dynamic Sorption Vapor and Infra-Red). This global method is an experimental way to characterise plant cell wall molecules of fractions by Thermal Gravimetric Analysis following by a mathematical method to have a detailed estimation of the cell wall composition and the interactions between plant macromolecules. The analyzed hemp shiv presents proportions of 2.5 ± 0.6% of water, 4.4 ± 0.2% of pectins, 42.6 ± 1.0% (Hemicellulose–Cellulose), 18.4 ± 1.6% (Cellulose–Hemicellulose), 29.0 ± 0.8% (Lignin–Cellulose) and 2.0 ± 0.4% of linked lignin.     

A Glycan Array-Based Assay for the Identification and Characterization of Plant Glycosyltransferases

Growing plants with modified cell wall compositions is a promising strategy to improve resistance to pathogens, increase biomass digestibility, and tune other important properties. In order to alter biomass architecture, a detailed knowledge of cell wall structure and biosynthesis is a prerequisite. We report here a glycan array-based assay for the high-throughput identification and characterization of plant cell wall biosynthetic glycosyltransferases (GTs). We demonstrate that different heterologously expressed galactosyl-, fucosyl-, and xylosyltransferases can transfer azido-functionalized sugar nucleotide donors to selected synthetic plant cell wall oligosaccharides on the array and that the transferred monosaccharides can be visualized “on chip” by a 1,3-dipolar cycloaddition reaction with an alkynyl-modified dye. The opportunity to simultaneously screen thousands of combinations of putative GTs, nucleotide sugar donors, and oligosaccharide acceptors will dramatically accelerate plant cell wall biosynthesis research.     

Stress induced plant resistance and enzyme activity varying in cucumber

When pathogens penetrate plant cells, some chemical secretions are elicited, and the mechanical signals in plant cell may be induced by the simultaneous physical pressure to change. Based on the previous cognitions, we investigated the plant resistance and the variation of anti-disease enzyme activity in cucumber leaves after mechanical stress loading. Results showed that the appropriate mechanical stimulation could significantly improve plant resistance and alter the activity of phenylalanine ammonial lyases (PAL) and POD, leading to synthesis of lignin. However, we found that the effects of the stress on these cellular fundamental events were eliminated when the adhesion between plasma membrane and cell wall was disrupted. We speculated that mechanical signal transduction in plants depend on the adhesion of plasma membrane–cell wall.     

The accumulation of phytoalexin in cucumber plant after stress

During the course of pathogens penetrating the plant cell, besides of chemical secretion, the pathogens may cause mechanical signal by the physical pressure on the plant cell. In the current study, we use the pressure as the stress signal to study the induction in plant resistance and the effect of accumulation of phytoalexin. We found that stress can induce the resistance in cucumber seeding significantly. Peptides contained RGD motif can specific block the adhesion between plant cell wall and plasma membrane. When breaking the plant cell wall and plasma membrane by using RGD peptides, the stress induction effect is almost absolutely eliminated. The results of assay with TLC and HPLC showed that stress stimulation could increase the accumulation of cucumber seeding phytoalexin. So, we can conclude that the accumulation of phytoalexin is one possible reason of improve the stress induced resistance. When block the adhesion between plant cell wall and plasma membrane by RGD, there are only part of accumulation of phytoalexin. The results suggest that stress induced resistance and accumulation of phytoalexin of plant is required for the adhesion of plant cell wall–plasma membrane.     

A Glycan Array‐Based Assay for the Identification and Characterization of Plant Glycosyltransferases

Growing plants with modified cell wall compositions is a promising strategy to improve resistance to pathogens, increase biomass digestibility, and tune other important properties. In order to alter biomass architecture, a detailed knowledge of cell wall structure and biosynthesis is a prerequisite. We report here a glycan array‐based assay for the high‐throughput identification and characterization of plant cell wall biosynthetic glycosyltransferases (GTs). We demonstrate that different heterologously expressed galactosyl‐, fucosyl‐, and xylosyltransferases can transfer azido‐functionalized sugar nucleotide donors to selected synthetic plant cell wall oligosaccharides on the array and that the transferred monosaccharides can be visualized “on chip” by a 1,3‐dipolar cycloaddition reaction with an alkynyl‐modified dye. The opportunity to simultaneously screen thousands of combinations of putative GTs, nucleotide sugar donors, and oligosaccharide acceptors will dramatically accelerate plant cell wall biosynthesis research.     

导电聚合物在纤维状能源器件中的应用进展

Conductive polymers implemented in fibrous energy devices have drawn considerable attention because of their economic importance, good environmental stability, and electrical conductivity. Conductive polymers demonstrate interesting mechanical, electronic, and optical properties, controllable chemical and electrochemical behavior, and facile processability. This review elaborates on the latest research in conductive polymers in fibrous energy devices, such as fibrous supercapacitors, fibrous solar cells, and fibrous integrated energy devices. The performance requirements of these fibrous energy devices, with specific reference to related materials, fabrication techniques, fiber structure, and electronic transport as well as mechanical functionality, are also reviewed in this paper.