Dietary fibre fractions in cereal and cereal-containing products in Britain

The values for dietary fibre in the current UK food tables were obtained using a fractionation method which involved digestion of starch with a takadiastase preparation. For the revision of the food tables new values for the dietary fibre in cereal and cereal-containing meat products were obtained by an improved fractionation method which used a mixture of amyloglucosidase and α-amylase to digest starch. The full details of this analytical method are given, along with the fibre components which were found in 138 cereal-containing foods. This method produced higher values than the previous method in most processed cereal products. Also the levels of pentoses in the non-cellulosic polysaccharide fraction and of lignin residues are greater. The study considerably extends the range of cereal-containing foods for which the amount of dietary fibre and its components has been determined.     

Sources of error in dietary fibre analysis

The following error sources in the present dietary fibre (DF) analytical methods were investigated: (1) the omission of the protease treatment of samples may modify the results by increasing the Klason lignin fraction and altering the content and/or distribution of polysaccharides; (2) some soluble dietary fibre (SDF) constituents can be retained in the insoluble dietary fibre (IDF) matrix affecting the insoluble and soluble fraction distribution; (3) protein, ash and blank corrections in gravimetric analysis involve a lack of precision, over- or undervaluing the actual DF contents; (4) the Klason lignin fractions obtained by acid hydrolysis of DF residues are made up of different components and artifacts besides lignin.

These studies included both new observations and additional quantitative evidence on error sources previously mentioned in the literature. In some cases the published methods were modified to emphasize the methodological errors.     

Studies on dietary fibre. A method for the analysis and chemical characterisation of total dietary fibre

A procedure for the analysis of total dietary fibre (including non-starchy polysaccharides and Klason lignin) is described. The method consists of extraction of homogenised and/or milled foodstuffs with 80% ethanol and chloroform, and analysis of acidic and neutral polysaccharide constituents, starch and Klason lignin in the residue. Uronic acid constituents were determined by a decarboxylation method, neutral sugar constituents as alditol acetates by a gas-liquid chromatographic method, starch by an enzymic method, and Klason lignin gravimetrically. The sum of anhydrosugars, anhydrouronic acids and Klason lignin from which the starch content is subtracted provides a measure of the total dietary fibre. The method described is reproducible, fairly rapid and gives informative quantitative characterisation of the fibre constituents.     

The isolation and analysis of cell wall material from the alcohol-insoluble residue of cabbage (Brassica oleracea var. capitata)

Cell wall material (CWM) was isolated from the wet ball-milled alcohol-insoluble residue of cabbage by treatment with Pronase, phenol-acetic acid-water and 90% aqueous dimethyl sulphoxide to remove precipitated proteins, starch and other intracellular compounds. Some solubilisation (mainly of pectic material) occurred during the purification stages. Methylation analysis of the cold water-soluble polysaccharides showed that the main neutral glycosidic linkages in descending order of concentration, were: non-reducing terminal arabinose groups, 5-linked arabinose and 4-linked galactose. The CWM contained a high level of arabinose-containing pectic polysaccharides. The main linkages present in the non-cellulosic polysaccharides were 4-linked galacturonic acid, non-reducing terminal arabinose groups and 5-linked arabinose; doubly branched arabinose residues were also present. Sequential extraction of the CWM by aqueous inorganic solvents yielded further information on the types of polysaccharides present. The general structural features of the CWM are discussed in the light of these results.     

Loss of selected water-insoluble polysaccharides and component neutral sugars from swede (Brassica napus (cv. danestone)) and cereal bran measured during digestion in the pig caecum

Sources of dietary fibre with a high pentose sugar content have been shown to have the greatest effect in promoting faecal bulking, though no underlying reason for this has been found. Pentose-containing polysaccharides in dietary fibre are, in isolation, as degradable as other polysaccharides, though their known association with lignin could be important in helping to maintain the structural integrity and hence the bulking ability of a fibre source. Using a modified nylon bag technique, the potential digestibility of fibre prepared from a source rich in pentose sugars (cereal bran) and a source poor in pentose sugars (Swede; Brassica napus, cv. Danestone) was estimated in the pig caecum. Swede fibre was effectively completely degraded (within 18 h) but in bran 100% digestion was not achieved even with extended incubation. Rates of fibre component loss, estimated from material recovered from the nylon bags, showed that different fibre components were degraded at different rates and that the rate of degradation was not always linear. In swede xylose was less readily lost than other fibre components and the rate was non-linear whilst in bran xylose was preferentially lost and at a linear rate. In bran arabinose was less readily lost. The results showed that the bulking effects of fibre sources with a high pentose sugar content were unlikely to be due solely to pentose content. Differences in rates of digestion suggested that different linkage groups contained within a component may be able to modify the degree of fibre digestion, most probably by the linkage of specific pentosans to lignin.     

Analysis of carbohydrates in seven edible fruits of Bangladesh

Dry matter, ash, lignin, starch and soluble and insoluble dietary fibre contents of the edible parts of seven fruits of Bangladesh were determined. Analysis of the low molecular weight carbohydrates showed that all the fiuits, except lukluki and hogplum, contained substantial amounts of these materials of which glucose and fiuctose were the main components. The main constituent of the polysaccharides in all the fruits was glucose. The dietary fibre contents of the dry fruits ranged from 29% to 79%. Lukluki has by far the best combination of low fiee sugars and high dietary fibre, and pineapple the worst.     

Composition of Dietary Fiber: Neutral and Acidic Sugar Composition of the Alcohol Insoluble Residue from Human Foods

The alcohol insoluble residue (AIR) isolated from 12 foods was acid hydrolyzed and analyzed for neutral and acidic sugars. Aliquots taken at 1 hr were reduced, acetylated and analyzed for neutral sugar content with GLC. Glucose from cellulose, starch and non-cellulosic polysaccharides was analyzed with colorimetric methods. The predominant sugars present in the dietary fiber were arabinose, xylose, galactose, glucose and uronic acids. Pectin and hemicellulose together comprised the majority of cell wall polysaccharides. Samples high in starch generally contained the greatest amounts of dietary fiber and the least amount of water on a fresh plant basis.     

Effects of simulated digestion in vitro on cell wall polysaccharides from kiwifruit (Actinidia spp.)

Cell wall polysaccharides are resistant to digestion and absorption in the human small intestine and are considered to be delivered to the colon in a chemically unaltered state. In this paper, pulp from green and gold kiwifruit was subjected to in vitro upper-intestinal tract digestion and the chemical and physical changes to cell wall polysaccharides (dietary fibre) were investigated. Yields of insoluble fibre decreased slightly with simulated digestion while soluble fibre yields increased. Constituent sugar and glycosyl linkage analysis of the soluble and insoluble fibre fractions revealed that the chemical composition and structure of the non-starch polysaccharides remained largely unchanged. However, the degree of methylesterification of galacturonic acid residues present in the pectin-rich soluble fibre fractions of both fruit decreased with treatment; size-exclusion chromatography detected changes in the molecular weight profiles of these fractions. These changes may affect the physicochemical properties and fermentability of kiwifruit dietary fibre in the large intestine.     

莲藕渣中多糖的提取及性质初步研究

本实验综合利用提取淀粉后的莲藕渣提取水溶性多糖和不溶性膳食纤维,并对水溶性多糖的结构及不溶性膳食纤维的特性进行了初步研究。通过水提醇沉、Sevag法去蛋白得到粗多糖NPh,得率为2.50%。离子交换柱层析法分离纯化出莲藕多糖NPh1和NPh2,凝胶过滤柱色谱及高效液相色谱仪检测多糖纯度,证明NPh2为纯品,其相对分子量>2000kD,是一种酸性杂多糖,单糖组成为半乳糖,阿拉伯糖、鼠李糖、葡萄糖、岩藻糖和木糖,摩尔比依次为:26.74;16.17:5.69:5.49:2.31:1。利用碱化学法提取不溶性膳食纤维NDFh,得率为26.97%。用2.0%H2O2进行了脱色。NDFh的持水性和溶胀性分别为7.58g/g和9.0ml/g。     

New potato fibre for improvement of texture and colour of wheat bread

The aim of this project was to compare the functional properties of five fibre fractions by baking of wheat bread by substitution 0, 4, 8 and 12 w/w% of wheat flour using dry potato pulp (Fibre 1), a commercial potato fibre (Fibre 2), two fibre prepared from potato pulp by enzymatic hydrolysis (Fibre 3 and 4), and one solubilised fibre (Fibre 5). The effect of chemical composition of fibre on texture, colour, specific weight and volume of wheat bread was studied using objective methods for measurement of texture characteristics, colour (L, a, b) and sensory analysis. Dry potato pulp, Potex (Fibre 2) and two enzymatically prepared fibre powders (Fibre 3 and 4) with a high concentration of lignin and insoluble non-starch polysaccharides (INCP) had a detrimental effect on bread quality by substitution of more than 8% of the wheat flour by fibre. The detrimental effect was mainly due to increased hardness, deformation energy, modulus and gumminess. Multiple linear regression analysis with forward selection was used for determination of the relationship between quality characteristics and of soluble non-starch polysaccharides (SNSP), insoluble non-starch polysaccharides (INCP), cellulose and lignin. The enzymatic solubilised fibre (Fibre 5) with a high concentration of soluble fibre and a low concentration of cellulose and lignin could be used for substitution of at least 12% wheat flour for baking of bread with an attractive colour, delicious texture and flavour.     

Dietary fibre in Hungarian foods measured by the Englyst NSP procedure and the AOAC Prosky procedure: a comparison study

Seventeen individual Hungarian foods and ten duplicate meals were analysed for dietary fibre by two current methods; the Englyst procedure (an enzymic-chemical method) for measuring dietary fibre as plant cell-wall non-starch polysaccharides (NSP) and the Prosky procedure (an enzymic-gravimetric method). The results obtained by these two methods are compared. The values obtained by the Prosky method are higher than those obtained by the Englyst method for 16 of the 17 individual foods and for all of the meal samples. National dietary guidelines recommend an increased intake of dietary fibre in the form of fruits, vegetables and whole grains. NSP values for unfortified plant foods provide a reliable marker for the cell-wall material present in the recommended, largely unrefined, plant foods. The Prosky values can represent the measurement of a range of materials formed during food processing and thus do not serve as a reliable guide to the composition of food products or the recommended, naturally occurring high-fibre diet.     

Cereal non-cellulosic polysaccharides: structure and function relationship - an overview

The non-cellulosic polysaccharides present in cereals (2-8%) are mostly arabinoxylans, (1 --> 3),(1 --> 4)-beta -glucans, pectins and arabinogalactans. Of these, the arabinoxylans are known to absorb large amounts of water and influence significantly the water balance, rheological properties of dough, and the retrogradation of starch and bread quality. (1 --> 3),(1 --> 4)-beta -glucans are known as biological response modifiers (BMS) as they are believed to modulate the immune response. Cereal Pectins and arabinogalactans form a very small amount and do not contribute substantially to the functionality of noncellulosic polysaccharides. Detailed structural investigations on cereal hetero xylans using modern techniques were initiated in the 1990s and still pose a challenge to carbohydrate chemists because of their structural complexity. Nutritionally, they are classified under "unavailable carbohydrates" (dietary fiber) along with lignin and cellulose and are known to have beneficial effects in alleviating disease symptoms such as diabetes, atherosclerosis, and colon cancer. In this review isolation, purification, characterization, structural elucidation, functional, and nutritional attributes of cereal heteroxylans are covered with particular emphasis on recently characterized finger millet arabinoxylans.     

Dietary fibre concentrates produced from papaya by-products for agroindustrial waste valorisation

In this work, papaya agroindustrial wastes were treated with ethanol and subsequently dehydrated to produce pulp or peel dietary fibre concentrates (DFCs). Hot air convection (CV) and microwave (MW) assisted dehydration were studied. The DFCs produced were mainly composed by cell wall polymers such as cellulose, lignin, proteins and non-cellulosic carbohydrates. It was found that convective drying produced DFCs with lower uronic acid content than microwave drying. Besides, pulp DFCs dehydrated by MW presented higher values for hydration properties, compared to those reported in literature. Peel DFCs presented better antioxidant properties than those from the pulp. Use of peel tissue, as well as CV produced DFCs with higher values of glass transition temperature. The characteristics found in the DFCs allow concluding that these products may be added in a diverse range of food products, granting benefits that would normally be obtained using several additives.     

Fiber and lignin analysis in concentrate, forage, and feces: detergent versus enzymatic-chemical method

Hemicelluloses, cellulose, and lignin contents of contrasting feeds, with emphasis on concentrate ingredients and complete concentrates, were analyzed using the Van Soest detergent procedure (analyzing neutral detergent fiber, acid detergent fiber, and acid detergent lignin) and the enzymatic-chemical procedure (analyzing cellulose, soluble and insoluble noncellulosic polysaccharides, and Klason lignin). Also, feces from cows fed concentrates differing in carbohydrate composition were analyzed by the 2 procedures. The correlation between acid detergent lignin and Klason lignin was significant, but not as close as the one between individual structural polysaccharides measured with the 2 procedures. The correlation between the results of the 2 procedures was highly significant for apparent cellulose digestibility, as were the correlations between digestibilities of hemicelluloses with total as well as with insoluble noncellulosic polysaccharides. The relationship between dietary lignin content and fiber digestibility was weak. The exclusion of a group of cows fed a concentrate with apple pulp, however, improved the respective correlations. Klason lignin correlated more closely with the measured fiber digestibility than acid detergent lignin. The study showed that results of the detergent method were comparable to those of the enzymatic-chemical method with cellulose, hemicelluloses, and their digestibilities. However, acid detergent lignin was much lower than Klason lignin. When the carbohydrate composition of concentrate varied widely, lignin was not suitable for the prediction of fiber digestibility.     

Effect of heat treatment on the dietary fibre contents of potato and tomato

The effects of autoclaving at 100, 120 and 130°C, baking in an oven, and microwave heating on the dietary fibre (DF) content and composition of potato and tomato were studied at normal pH and after acidification. The fibres were fractionated by sequential hydrolysis, and the sugar compositions were determined by gas chromatography (a modification of Englyst's method). All heat treatments appeared to increase the total DF content of the potato; the fraction analysing as 'cellulose' showed the major change, which was probably due to the retrogradation of starch. Autoclaving, especially at 130°C, reduced the total DF of tomato, while baking increased it. Excessive autoclaving may have hydrolysed some of the water soluble non-cellulosic polysaccharides (w.s. NCP), and solubilized a part of the water insoluble (w.i.s.) NCP. Baking increased the w.i.s. NCP and cellulose fractions, in particular. Slight acidification caused only minor additional changes in the fibre fractions.     

Liver paté enriched with dietary fibre extracted from potato fibre as fat substitutes

This experiment included studies of the functionality of three new enzymatically extracted fibres as ingredients in pig liver paté prepared using reduced amounts of pig fat with dry potato pulp and a commercial potato fibre (Potex) as references. The measured quality characteristics included colour, flavour, and texture profile analysis. Dry potato pulp, Potex and two of the new enzymically extracted fibre 1 and 2 with high contents of cellulose and lignin resulted in very hard patties with a high level of deformation energy, gumminess, and modulus that had a detrimental effect on paté texture and flavour. The enzymatically extracted fibre 3 with a low content of cellulose and lignin and a high content of soluble non-starch polysaccharides (SNSP) resulted in patties with a very delicious texture and flavour and values of the measured texture characteristics determined by texture profile analysis. The colour of the patties processed using the enzymatically extracted fibre 3 were darker, more red and less yellow compared to patties processed using Potex, dry potato pulp and new fibre 1 and 2. Baking loss that varied from 9.2 to 11.3 g/100 g was the lowest for patties processed using the new extracted fibre 3. The content of total dietary plant fibre in liver patties varied from 4.0 to 6.2 g/100 g paté.     

Kinetic analysis of bile salt passage across a dialysis membrane in the presence of cereal soluble dietary fibre polymers

The kinetics of passage of a model bile salt and complete porcine bile across a dialysis membrane, in the presence and absence of two cereal-derived soluble dietary fibre polysaccharides, were studied as a model for passage across the unstirred water layer that lines the small intestine. A first-order kinetic analysis allowed rate coefficients to be derived which quantified the effectiveness of barley mixed linkage β-glucan and wheat arabinoxylan in retarding the transport of bile. For both, a model bile salt and complete porcine bile, rate coefficients decreased with both concentration and viscosity. A combination of viscosity and molecular interaction effects is suggested to control the effect of the two polysaccharides on the transport of bile.     

Laminarin in the dietary fibre concept

Dietary fibres consist of edible plant polysaccharides that are resistant to digestion and absorption in the human small intestine but undergo complete or partial fermentation in the colon. Seaweeds, notably Laminaria spp, are particularly rich in polysaccharides resistant to hydrolysis in the upper gastrointestinal tract and are, in consequence, considered as dietary fibres. Most of the carbohydrates from Laminaria spp are thought to be indigestible by humans. The main storage polysaccharide of these algae is laminarin, a β‐polymer of glucose. The aims of this work were, on the one hand, to compare various methods of extraction of laminarin by partial characterisation of the product obtained and, on the other hand, to study the fate of this polysaccharide and its effects in the gastrointestinal tract in order to determine its potential as a dietary fibre in human nutrition. Among four methods tested to extract laminarin, the best appeared to be a hot HCl‐based method. Human digestive enzymes did not hydrolyse laminarin, so this polysaccharide can be considered as a dietary fibre. After ingestion by rats, this polysaccharide was not found in faeces of these animals. It did not increase the intestinal transit and stool output in vivo, but it increased the contractile response of the stomach to acetylcholine in vitro. Copyright © 2004 Society of Chemical Industry     

An investigation of lignin extraction from dietary fibre using acetyl bromide

Acetyl bromide is a suitable reagent for the extraction of lignins from woody material and grasses but lignins present in vegetables do not give the expected absorbance spectrum. Treatment of the vegetable fibre with either organic solvents or dilute acid or the removal of protein and hemicellulose does not alter the absorbance spectrum of lignins present in vegetables. All methods used for lignin extraction are quantitatively consistent and show only a trace of lignin to be present in vegetable fibre.     

A rapid method for determining the carbohydrate component of dietary fibre

A simplified procedure for the determination of the non-starch polysaccharides in foods is described. Starch is removed by treatment with heat-stable α-amylase and resistant starch by treating with dimethyl sulphoxide (DMSO) and amyloglucosidase. Total neutral sugars and uronic acids are then measured colorimetrically in the acid hydrolysates of the starch-free material.The method is more rapid than the complex fractionation procedures (Southgate, 1969; Selvendran et al., 1979; Englyst, 1981) but does not provide a detailed composition. The time per sample compares favourably with the gravimetric assay of Asp et al. (1983) and a direct measure of the carbohydrate content of the dietary fibre fraction is obtained. The results compare favourably with those obtained by the complex method of Englyst et al. (1982). The method is applicable to a range of foods, both raw and cooked, and should have application in the routine analysis of dietary fibre since it is comparatively rapid and does not require complex or expensive equipment.