Determination of polydextrose as dietary fiber in foods

Polydextrose (Litesse) provides physiological effects consistent with dietary fiber. However, AOAC methods for measuring total dietary fiber (TDF) in foods include an ethanol precipitation step in which polydextrose and similar carbohydrates are discarded and therefore not quantitated. This study describes a method developed to quantitate polydextrose in foods. The new method includes water extraction, centrifugal ultrafiltration, multienzyme hydrolysis, and anion exchange chromatography with electrochemical detection. Six foods were prepared with 4 levels of polydextrose to test the ruggedness of the method. Internal validation demonstrated the ruggedness of the method with recoveries ranging from 83 to 104% with an average of 95% (n = 24) and relative standard deviation of recoveries ranging from 0.7 to 13% with an average of 3.3% (n = 24). The value is added to that obtained for dietary fiber content of foods using the AOAC methods, to determine the TDF content of the food.     

Importance of enzyme purity and activity in the measurement of total dietary fiber and dietary fiber components

A study was made of the effect of the activity and purity of enzymes in the assay of total dietary fiber (AOAC Method 985.29) and specific dietary fiber components: resistant starch, fructan, and beta-glucan. In the measurement of total dietary fiber content of resistant starch samples, the concentration of alpha-amylase is critical; however, variations in the level of amyloglucosidase have little effect. Contamination of amyloglucosidase preparations with cellulase can result in significant underestimation of dietary fiber values for samples containing beta-glucan. Pure beta-glucan and cellulase purified from Aspergillus niger amyloglucosidase preparations were used to determine acceptable critical levels of contamination. Sucrose, which interferes with the measurement of inulin and fructooligosaccharides in plant materials and food products, must be removed by hydrolysis of the sucrose to glucose and fructose with a specific enzyme (sucrase) followed by borohydride reduction of the free sugars. Unlike invertase, sucrase has no action on low degree of polymerization (DP) fructooligosaccharides, such as kestose or kestotetraose. Fructan is hydrolyzed to fructose and glucose by the combined action of highly purified exo- and endo-inulinases, and these sugars are measured by the p-hydroxybenzoic acid hydrazide reducing sugar method. Specific measurement of beta-glucan in cereal flour and food extracts requires the use of highly purified endo-1,3:1,4 beta-glucanase and A. niger beta-glucosidase. Beta-glucosidase from almonds does not completely hydrolyze mixed linkage beta-glucooligosaccharides from barley or oat beta-glucan. Contamination of these enzymes with starch, maltosaccharide, or sucrose-hydrolyzing enzymes results in production of free glucose from a source other than beta-glucan, and thus an overestimation of beta-glucan content. The glucose oxidase and peroxidase used in the glucose determination reagent must be essentially devoid of catalase and alpha- and beta-glucosidase.     

Historical perspective as a guide for identifying and developing applicable methods for dietary fiber

A review is presented describing the nature and evolving definition of dietary fiber. The historical development of the current definition is discussed as are the efforts to develop analytical methods to support food labeling regulations. Also considered are the characterization and quantitation of resistance starch, a dietary starch that does not digest in the small intestine, behaves like dietary fiber and therefore may have potential as a health-related ingredient in foods. The current status of AOAC methodology is discussed along with the possibility of updating the definition of dietary fiber. The potential impacts of changing the dietary fiber definition on analytical issues and on food composition databases are also considered.     

Correlating detergent fiber analysis and dietary fiber analysis data for corn stover collected by NIRS

There exist large amounts of detergent fiber analysis data [neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL)] for many different potential cellulosic ethanol feedstocks, since these techniques are widely used for the analysis of forages. Researchers working in the area of cellulosic ethanol are interested in the structural carbohydrates in a feedstock (principally glucan and xylan), which are typically determined by acid hydrolysis of the structural fraction after multiple extractions of the biomass. These so-called dietary fiber analysis methods are significantly more involved than detergent fiber analysis methods. The purpose of this study was to determine whether it is feasible to correlate detergent fiber analysis values to glucan and xylan content determined by dietary fiber analysis methods for corn stover. In the detergent fiber analysis literature cellulose is often estimated as the difference between ADF and ADL, while hemicellulose is often estimated as the difference between NDF and ADF. Examination of a corn stover dataset containing both detergent fiber analysis data and dietary fiber analysis data predicted using near infrared spectroscopy shows that correlations between structural glucan measured using dietary fiber techniques and cellulose estimated using detergent techniques, and between structural xylan measured using dietary fiber techniques and hemicellulose estimated using detergent techniques are high, but are driven largely by the underlying correlation between total extractives measured by fiber analysis and NDF/ADF. That is, detergent analysis data is correlated to dietary fiber analysis data for structural carbohydrates, but only indirectly; the main correlation is between detergent analysis data and solvent extraction data produced during the dietary fiber analysis procedure.     

New method for determining total dietary fiber by liquid chromatography

The molecular weight limit of water-soluble dietary fiber (SDF) determined by the Prosky method was studied by liquid chromatography (LC). It was confirmed that only SDF with an average degree of polymerization of 12 or higher can be determined by the Prosky method. Total dietary fiber (TDF) was determined by 2 additional methods using LC. In the first method, the total quantity of insoluble dietary fiber (IDF) and high molecular weight SDF (HMSDF) was determined according to the modified Prosky method (MES-TRIS buffer-based). The quantitatively collected final filtrate was analyzed by LC for the quantity of low molecular weight SDF (LMSDF), and the 2 quantities were totaled to obtain TDF. TDF values thus determined for rice, polished or unpolished, soybean flour, and pressed barley were higher than those determined by the Prosky method by approximately 6, 3.5, and 3.5%, respectively. In the second method, direct determination by LC analysis was done on samples after enzymatic treatment according to the Prosky method. Results showed that the determination of LMSDF, in particular, was highly accurate and more effective. In both of these methods, the quantity of LMSDF was determined from its chromatographic peak area ratio to glucose as an internal standard, which was produced by hydrolysis.     

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.     

Synthetic oligosaccharides as tools to demonstrate cross-reactivity between polysaccharide antigens

Escherichia coli O148 is a nonencapsulated enterotoxigenic (ETEC) Gram negative bacterium that can cause diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans. The surface-exposed O-specific polysaccharide (O-SP) of the lipopolysaccharide of this bacterium is considered both a virulence factor and a protective antigen. It is built up of the linear tetrasaccharide repeating unit [3)-α-L-Rhap-(1→2)-α-D-Glcp-(1→3)-α-D-GlcNAcp-(1→3)-α-L-Rhap-(1→] differing from that of the O-SP of Shigella dysenteriae type 1 (SD) only in that the latter contains a D-Galp residue in place of the glucose moiety of the former. The close similarity of the O-SPs of these bacteria indicated a possible cross-reactivity. To answer this question we synthesized several oligosaccharide fragments of E. coli O148 O-SP, up to a dodecasaccharide, as well as their bovine serum albumin or recombinant diphtheria toxin conjugates. Immunization of mice with these conjugates induced anti-O-SP-specific serum IgG antibody responses. The antisera reacted equally well with the LPSs of both bacteria, indicating cross-reactivity between the SD and E. coli O148 O-SPs that was further supported by Western-blot and dot-blot analyses, as well as by inhibition of binding between the antisera and the O-SPs of both bacteria.     

Guarnt® bland,a reduced odor stabilizer and soluble dietary fiber

The odor and flavor of guar gum may emanate from the breakdown of lipid, protein and/or isoflavones. Guar gum is a galactomannan isolated from the annual plant, Cyamopsis tetragonolobus, Guar is widely used as a thickening agent but due to its characteristic off-flavor and odor, its usage level has been limited. GuarNT bland, subjected to a proprietary process to reduce its off-flavor and odor, offers the food formulator more options. GuarNT bland can be subjected to a prehydration process to improve its dispersion and increase hydration rate and avoid lumping problems during large-scale production. It is used as a thickening agent, suspending agent and a “natural” source of soluble dietary fiber (80% minimum, dry basis). Rheological data using a programmable Brookfield rheometer, hexanal levels (index of grassy flavor), PCA analyses (Aroma Scan, Foss NA) and sensory tests by trained panelists were obtained. Prototype formulations using GuarNT Bland are available and usage levels permitted by CFR are included.     

Synthesis of oligosaccharides by using levulinic ester as an hydroxyl protecting group

The fast, selective and mild removal of levulinyl groups with hydrazine from galactose, which also carries hydroxyl functions protected with acetyl groups, enables, under Koenigs-Knorr conditions, the synthesis of a trimer containing β-linked galactoses.     

Stereoselective assembly of complex oligosaccharides using anomeric sulfonium ions as glycosyl donors

The development of selectively protected monosaccharide building blocks that can reliably be glycosylated with a wide variety of acceptors is expected to make oligosaccharide synthesis a more routine operation. In particular, there is an urgent need for the development of modular building blocks that can readily be converted into glycosyl donors for glycosylations that give reliably high 1,2-cis-anomeric selectivity. We report here that 1,2-oxathiane ethers are stable under acidic, basic, and reductive conditions making it possible to conduct a wide range of protecting group manipulations and install selectively removable protecting groups such as levulinoyl (Lev) ester, fluorenylmethyloxy (Fmoc)- and allyloxy (Alloc)-carbonates, and 2-methyl naphthyl ethers (Nap). The 1,2-oxathiane ethers could easily be converted into bicyclic anomeric sulfonium ions by oxidization to sulfoxides and arylated with 1,3,5-trimethoxybenzene. The resulting sulfonium ions gave high 1,2-cis-anomeric selectivity when glycosylated with a wide variety of glycosyl acceptors including properly protected amino acids, primary and secondary sugar alcohols and partially protected thioglycosides. The selective protected 1,2-oxathianes were successfully employed in the preparation of a branched glucoside derived from a glycogen-like polysaccharide isolated form the fungus Pseudallescheria boydii , which is involved in fungal phagocytosis and activation of innate immune responses. The compound was assembled by a latent-active glycosylation strategy in which an oxathiane was employed as an acceptor in a glycosylation with a sulfoxide donor. The product of such a glycosylation was oxidized to a sulfoxide for a subsequent glycosylation. The use of Nap and Fmoc as temporary protecting groups made it possible to install branching points.     

铜藻膳食纤维可食用膜的制备及风味分析

以铜藻膳食纤维为原料制备可食用膜,促进对利用程度不高的铜藻膳食纤维的精深加工.研究了料液比、甘油含量、增稠剂含量对铜藻膳食纤维可食用膜透明度的影响,通过单因素试验确定最佳制备条件为:料液比1:30、甘油含量为2％,增稠剂羟甲基纤维素钠添加量为1％,在此条件下可食用膜的透明度最高为15.87％.对铜藻膳食可食用膜的风味成...     

Using collagen fiber as a template to synthesize hierarchical mesoporous alumina fiber

Hierarchical mesoporous alumina fiber was synthesized by using collagen fiber as the template, and characterized by means of scanning electron microscopy, transmission electron microscopy, N2 adsorption techniques, X-ray photoelectron spectroscopy, and X-ray diffraction. The alumina fiber obtained is approximately 1-4 microm in outer diameter and 0.5-1 mm in length. The pore size distribution of the alumina fiber is narrow (2-20 nm), and its pore size is controllable by varying preparation methods. This study indicates that collagen fiber, which has hierarchical supermolecular structure, could be used as an ideal template to prepare well-defined porous metal oxide fibers.     

Solubilization of oligosaccharides into chloroform by their incorporation into polystyrene as pendant groups

Solubilization of hydrophilic saccharide chains into organic solvents has been attempted by incorporating saccharide-substituted styrene unit into polystyrene main chain. Lactose-, maltopentaose, and amylose-substituted styrene monomers were copolymerized with styrene. Resulting chloroform-soluble copolymers were characterized, and structural formation was investigated. Copolymers of lactose-substituted styrene and maltopentaose-substituted styrene with styrene were dissolved into chloroform. The chloroform-soluble polymers contained about 12 disaccharide lactose chains or 1.7 maltopentaose chains as the pendant groups in one polystyrene molecule. Chloroform-insoluble methyl orange was dissolved into chloroform with the help of chloroform-soluble polystyrene having some saccharide chains. On the other hand, when an amylose-substituted styrene unit was inserted in a polystyrene chain, the resulting polymer became insoluble into chloroform. Amylose polysaccharide of DP_n = ∼24 was not dissolved into chloroform by this method.     

3-Mercaptopropanol as a traceless linker for chemical and enzymatic synthesis of oligosaccharides

The reducing end of protected carbohydrates can be equipped with a series of aglycones via the photochemical installation of a 3-mercaptoethanol linker. This linker is stable during chemical and enzymatic glycosylation reactions but can be activated readily and efficiently to couple oligosaccharides with different nucleophiles. This approach provides straightforward access to a range of molecules that serve as probes for carbohydrate modifying enzymes. [reaction: see text].     

An integrated procedure for the measurement of total dietary fibre (including resistant starch), non-digestible oligosaccharides and available carbohydrates

A method is described for the measurement of dietary fibre, including resistant starch (RS), non-digestible oligosaccharides (NDO) and available carbohydrates. Basically, the sample is incubated with pancreatic α-amylase and amyloglucosidase under conditions very similar to those described in AOAC Official Method 2002.02 (RS). Reaction is terminated and high molecular weight resistant polysaccharides are precipitated from solution with alcohol and recovered by filtration. Recovery of RS (for most RS sources) is in line with published data from ileostomy studies. The aqueous ethanol extract is concentrated, desalted and analysed for NDO by high-performance liquid chromatography by a method similar to that described by Okuma (AOAC Method 2001.03), except that for logistical reasons, d-sorbitol is used as the internal standard in place of glycerol. Available carbohydrates, defined as d-glucose, d-fructose, sucrose, the d-glucose component of lactose, maltodextrins and non-resistant starch, are measured as d-glucose plus d-fructose in the sample after hydrolysis of oligosaccharides with a mixture of sucrase/maltase plus β-galactosidase.     

Polyamide 11 as a hard elastic fiber

Fibers of nylon-11 annealed in contact with formic acid (90%) have the same unit cell as solution grown crystals; the basal planes of the lamellar crystals are parallel to (ool) crystallographic planes. The melting curves and the stress-strain curves of such annealed fibers are presently reported. The temperature corresponding to the maximum of the melting peak increases with the annealing temperature: an increase of 10°C is observed although the long spacings keep the constant value of 12 nm. Lower elastic modulus but higher strains are obtained with increasing annealing temperatures. Such annealed samples can undergo large extension without occurrence of necking and plastic flow.