EVALUATION OF DIETARY FIBER IN POTATO CRISPS: INFLUENCE OF THE ANALYTICAL METHOD USED

Dietary fiber in ready salted potato crisps was determined by two methods, i.e., the official AOAC method, and the modified method of Englyst, recommended in the U. K. The ultimate aim was to compare the results and to evaluate the advantages and limitations of each method for the analysis of this food in order to obtain a figure to be included on the package. The AOAC method is an enzymatic-gravimetric procedure to determine the total dietary fiber (TDF). The Englyst method consists of an enzymatic-chemical extraction and fractionation of the nonstarch polysaccharides (NSP) and their subsequent determination as neutral sugars by GLC. We modified the original chromatographic method. The AOAC method gave a value of 5.39 g/100g (dry matter) for TDF, and the Englyst method of a value of 1.70 g/100g (dry matter) for NSP. It is assumed that the gravimetric method gives a higher fiber value than the Englyst method due to a contribution from retrograded starch. For this particular food, the AOAC method is faster and much easier to carry out and does not overestimate dietary fiber, if the resistant starch is regarded as part of it.     

Starch and non-starch polysaccharides in some cereal foods

The polysaccharide content of some cereal foods is reported, measured by a recently described technique. This method allows accurate determination of plant cell wall and other plant polysaccharides and identification and measurement of starch made resistant to digestion by α-amylase and pullulanase during food processing (resistant starch). The results reported are at variance with values for dietary fibre measured by other published methods by a factor of up to 10 in some foods. This is due partly to the failure of some methods to identify resistant starch separately from NSP and partly to other details of methodology. Implied in these findings is the need to critically assess methods used for the chemical determination of non-starch polysaccharides and the need to be cautious in interpreting dietary-fibre-intake data especially in population studies.     

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.     

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.     

Determination of total dietary fibre and available carbohydrates: A rapid integrated procedure that simulates in vivo digestion

The new definition of dietary fibre introduced by Codex Alimentarius in 2008 includes resistant starch and the option to include non‐digestible oligosaccharides. Implementation of this definition required new methodology. An integrated total dietary fibre method was evaluated and accepted by AOAC International and AACC International (AOAC Methods 2009.01 and 2011.25; AACC Method 32–45.01 and 32–50.01, and recently adopted by Codex Alimentarius as a Type I Method. However, in application of the method to a diverse range of food samples and particularly food ingredients, some limitations have been identified. One of the ongoing criticisms of this method was that the time of incubation with pancreatic α‐amylase/amyloglucosidase mixture was 16 h, whereas the time for food to transit through the human small intestine was likely to be approximately 4 h. In the current work, we use an incubation time of 4 h, and have evaluated incubation conditions that yield resistant starch and dietary values in line with ileostomy results within this time frame. Problems associated with production, hydrolysis and chromatography of various oligosaccharides have been addressed resulting in a more rapid procedure that is directly applicable to all foods and food ingredients currently available.

     

Effects of alkaline treatment on the structure of phosphorylated wheat starch and its digestibility

Phosphorylated wheat starch (PWS) was prepared with sodium trimetaphosphate and sodium tripolyphosphate (99/1, w/w), and the modified starch gave 88.8% total dietary fibre by the Prosky method and 68.7% resistant starch (RS) by the Englyst method. The stability of the phosphate esters in aqueous sodium hydroxide was investigated and related to total dietary fibre and RS contents. The phosphorylated starch was slurried (40%, w/w) at 40 °C for 4 h at pH 9.0, 10.0, 11.0, and 12.0. The phosphorus content of the PWS decreased from 0.37% to 0.29% after treatment at pH 12.0, whereas only a slight decrease in phosphorus content occurred after treatments at pH 9.0–11.0. Despite the 22% decrease in total phosphorus content, total dietary fibre content and RS content of the alkali-treated PWS changed only slightly. ³¹P nuclear magnetic resonance spectroscopy showed that after the alkali treatment at pH 12.0, cyclic monostarch monophosphate and monostarch diphosphate were not detectable and that the level of total monostarch monophosphate decreased from 0.077% to 0.067%. Conversely, distarch monophosphate increased from 0.17% to 0.20%, of ≈18%. The increase in distarch monophosphate (cross-linking) content after alkali treatment at pH 12.0 probably explained the retention of total dietary fibre and RS contents in the alkali-treated PWS.     

Dietary interview. I. Comparison between dietary history versus repeated daily recalls]

In the course of 12 months, 43 men and 53 women aged 30-40 years were subjected to 14 24-hours recalls and one dietary history concerned with their individual dietary habits. The mean values yielded by the first and the second method for energy, 4 nutrient groups and 8 food groups were statistically evaluated and compared with each other, from which the following conclusions can be drawn as to the reliability and the precision of the dietary history: 1. The dietary history permits the quantitative estimate of the energy and nutrient intake in groups of about 50 subjects with an error of less than 10%. Underestimation of the actual food intake is more likely than overestimation. 2. The same holds true for the quantitative estimate of the consumption of foods from great food groups. The method is considerably less precise in case of single food or irregularly consumed foods. The differences between the results from the two methods ranged from 0 to 25%. 3. The precision of the individual results obtained for energy and nutrient intake from the dietary history was +/- 20% with a probability of 80-90%. In 75% of the cases, the differences in the consumption of food groups as determined by the two methods were smaller than 20%. As to single foods, however, individual misestimations ranging from 30 to 50% are to be expected.     

Soybean seeds and its by-product okara as sources of dietary fibre. Measurement by AOAC and Englyst methods

The composition of soybean seeds and its by-product okara has been studied in this work. Dietary fibre was analysed by Englyst et al. method, by enzymatic–gravimetric methods of AOAC and by the quantification of the monomers obtained from the AOAC residues after acid hydrolysis (AOAC plus hydrolysis). Total dietary fibre by the enzymatic–gravimetric methods of AOAC in okara (55.48 g/100 g dry matter) is more than twice that of soybean seeds (24.37 g/100 g dry matter). The proportion IF/SF is 11 in okara and 6 in soybean seeds. Dietary fibre results from enzymatic–gravimetric AOAC methods are higher in okara and soybean seed samples than those from the Englyst method (okara: 41.14 g/100 g dry matter; soybean seeds: 15.05 g/100 g dry matter), and AOAC plus hydrolysis (okara: 44.91 g/100 g dry matter; soybean seeds: 16.38 g/100 g dry matter). In the case of the insoluble fibre from both samples, AOAC plus hydrolysis gives significantly (p < 0.001) higher values than the Englyst method, whilst for soluble fibre the opposite occurs (p < 0.001). The main monomers in soybean seeds and okara fibre are glucose, galactose, uronic acids, arabinose and xylose. The proportion of each monomer is similar in soybean seeds and okara, so the healthy properties of soybean seeds fibre are also claimed for okara.     

Evaluation of methods of analysis for dietary fibre using real foods and model foods

Rationale and objectives

There are several rational and empirical methods for the measurement of dietary fibre and its components. A selection of these methods were evaluated by investigation of a range of real foods and model foods with added resistant starch (RS), non-starch polysaccharides (NSP) and resistant oligosaccharide (RO) ingredients.

Methods

A range of rational methods were applied in determining specific carbohydrate constituents: RS, NSP and RO, including fructans. For comparison, empirical methods AOAC 991.43 (2001.03) and AOAC 2009.01 were applied, based on determination of gravimetric residues for high molecular weight and size-exclusion HPLC analysis of the ethanol filtrate for low molecular weight components.

Results

In general there was agreement between different rational methods for the analysis of RS and fructans, though there were notable exceptions for some product types. Comparison of methods for total RS and those that only measure the RS3 fraction, from retrograded starch, indicated that RS3 was the only type present for most processed products. This also explains the similar results obtained by AOAC 991.43 (2001.03) and AOAC 2009.01, though the latter is intended to recover other RS types as well. For many products there was agreement between results obtained by rational and empirical methods, though there were exceptions and the reasons for these are discussed.

Conclusion

Rational and empirical methods can both be used to determine dietary fibre in most situations. The information provided by rational methods is useful in identifying the specific carbohydrate constituents present in foods and can assist in determining whether added extracted and synthesised ingredients are ones that conform to the Codex and EU dietary fibre definition.     

The analysis of dietary fibre—the choices for the analyst

The analysis of dietary fibre (which is defined as the sum of lignin and the polysaccharides not digested by the endogenous secretions of the human digestive tract) presents several problems to the analyst. Dietary fibre is a mixture of substances derived from the structural materials of the plant cell wall and a range of polysaccharides of a non-structural nature either present naturally in foods or derived from food additives. The complete analysis of such a complex mixture would be difficult and time consuming and a number of practical alternatives have been used. These include methods based on the enzymatic removal of protein and starch to give an ?indigestible residue’? and procedures based on extraction with neutral detergent solutions. These procedures in their present form do not measure water-soluble components and therefore underestimate dietary fibre. More detailed methods in which the water-soluble and water-insoluble non-cellulosic polysaccharides, cellulose and lignin were measured separately are described. In these the non-cellulosic fraction was characterised in terms of its component sugars. It is suggested that methods of this type are necessary to characterise dietary fibre analytically in order to account for the properties of dietary fibre.     

Cauliflower (Brassica oleracea L), globe artichoke (Cynara scolymus) and chicory witloof (Cichorium intybus) processing by-products as sources of dietary fibre

By-products arising from vegetable processing activities have been assessed in relation to their potential application as sources of dietary fibre supplements in refined foods. Sources used were fresh cauliflower, globe artichoke and chicory witloof. Non-starch polysaccharide (NSP) content and composition of selected parts of each plant source have been measured from alcohol insoluble residues (AIR) and by fibre analysis, complemented by methylation analysis to characterise structural features of component polysaccharides. Results indicate that cauliflower upper stem NSP was similar to the floret (∽25 g kg⁻¹ fresh weight) and each was rich in pectic polysaccharides. Cauliflower lower stem was enriched in NSP (∽66 g kg⁻¹) due mainly to cellulose and xylan deposition, which resulted in a proportionate decrease in pectic polysaccharides. Artichoke stem (∽38 g NSP kg⁻¹) was similar to the receptacle (∽34 g NSP kg⁻¹) but bracts were heavily lignified. Chicory root and leaf bud were each rich in pectic polysaccharides but NSP content was much higher in the root (∽46 g kg⁻¹) than the leaf (∽8 g kg⁻¹). Results indicate that processing by-products, eg cauliflower upper stem, artichoke stem and chicory root, could prove useful as sources of pectic polysaccharide-rich supplements. However, polysaccharide composition and glycosidic linkage pattern also identified important structural differences between sources. The importance of ‘fibre type’ when considering development of food supplements is discussed. © 1998 SCI.     

A Rapid Method for the Determination of Soluble and Insoluble Dietary Fiber: Comparison with AOAC Total Dietary Fiber Procedure and Englyst's Method

Total dietary fiber (TDF) was measured in 16 foods by three methods: a rapid enzyme-NDF (neutral detergent fiber) procedure supplemented with a separate procedure for soluble (SOL) fiber, the AOAC TDF method and the comprehensive Englyst's procedure. The NDF+SOL method needed less operator time than the AOAC method and its TDF values were in agreement with the AOAC method (y = 0.98 -0.39; r = 0.997) and with the Englyst's method (y = 1.17 -0.19; r = 0.996). The constituent sugars of polysaccharides in NDF+SOL residues were similar to those by the Englyst's method, indicating an adequate estimation of dietary fiber in foods and food products.     

Dietary carbohydrates: classification by chemistry and physiology

Food carbohydrates consist of mono-, di-, oligo- and polysaccharides, the latter composed of starch and non-starch polysaccharides (NSP). The glycaemic response to both sugars and starches is dependent on the types of sugars present and the form of the starches, and ‘complex carbohydrates’ do not necessarily produce slower or lower glycaemic responses than the sugars. Carbohydrates not absorbed in the small intestine are fermented more or less extensively by the large intestinal microflora. There is a fundamental difference nutritionally between digestible and undigestible (‘unavailable’) carbohydrates. NSP, resistant starch (RS) and oligosaccharides are the main forms of undigestible carbohydrates. Dietary fibre is generally conceived as more or less synonymous with ‘unavailable’ carbohydrates. The nutritional effects of dietary fibre are related to its undigestibility in the small intestine, and to the physical and chemical properties of its constituent polysaccharides. Food structures built of dietary fibre as plant cell-walls, and also of other food components, are increasingly recognized as nutritionally important. Food databases should include as much specific and detailed information as possible on food carbohydrates. For food labelling, carbohydrates have to be divided into a number of nutritionally meaningful classes. A first classification should then aim at differentiating the digestible and undigestible carbohydrates, i.e. dietary fibre.     

The metabolisable energy value of foods

Methods for calculating the Metabolisable Energy (ME) of foods and diets are reviewed in the light of the current interest in diets high in dietary fibre. A new equation is proposed for the calculation of ME, taking into account the dietary fibre content of foods and its effects on the digestibility of proximate sources of energy. The equation has been tested against values for the ME of various diets determined by balance studies in human subjects, and gives results which agree within 3%. This agreement is much closer than that obtained with the other available methods for calculating ME, including those currently in use.     

Determination of carbohydrates in foods. II. Unavailable carbohydrates

A fractionation and analytical procedure is described for the measurement of the unavailable carbohydrates in foods. The scheme provides values for water-soluble polysaccharides, hemicellulose, cellulose and lignin. Tests used to investigate the reliability of the methods are reported and the results obtained with a range of foodstuffs are presented. From the results obtained it is possible to derive values for the composition of the cell-wall material of these foods. The results are in agreement with more detailed studies of the composition of the cell walls of plants.     

Fruit‐based functional foods I: production of food‐grade apple fibre ingredients

With the increased consumer interest in fibre‐enriched functional foods, industrial‐scale methods for functional fibre production are demanded. The development of a food‐grade fibre preparation method at lab scale that is feasible for industrial scale‐up is a pre‐requisite. This paper describes two lab‐scale fibre preparation methods that have potential to be scaled up to industrial setting for the production of fruit fibres containing desired bioactives and functionality. The two methods, one aqueous and the other ethanolic, were used to isolate fibres from Granny Smith apples (Malus domestica Borkh cv. ‘Granny Smith’). In the aqueous method, ground apple tissues were suspended in HEPES buffer (20 mM, pH 6.5), and then mechanically ruptured using an Ultra‐Turrax and ring grinder. Between steps, the cell‐wall materials were washed with the HEPES buffer. In the ethanolic method, ground apple tissues were stirred in 72% ethanol at 4 °C, filtered, re‐suspended in 72% ethanol and then washed. Microscopic examination and chemical analysis were performed on the resultant fibres. The aqueous method produced natural and uniform dietary fibres in the form of plant cell walls containing 0.282 g uronic acid per g dried fibre. By comparisons, the ethanolic method produced crude fibres containing only 0.182 g uronic acid per g dried fibre, the lower uronic acid content indicating the presence of impurities. Thus, the aqueous method appeared to be advantageous in terms of the retained pectic polysaccharide content and cost‐effectness for industrial scale‐up. Further characterisation using Folin‐Ciocalteu assay and high performance liquid chromatography indicates that the fibres obtained by the aqueous method contained significant amounts of phenolic compounds (2.6 mg catechin equivalent per g dried fibre). These results suggest that fibres obtained by the aqueous method may be more suitable for functional food applications where fibres with high pectic polysaccharide and beneficial phenolic antioxidants are preferred.     

Broad bean and pea by‐products as sources of fibre‐rich ingredients: potential antioxidant activity measured in vitro

BACKGROUND By‐products generated during the processing of plant food can be considered a promising source of dietary fibre as a functional compound. The dietary fibre composition, soluble sugars and antioxidant activity of the extractable polyphenols of pea and broad bean by‐products have been analysed in this study. RESULTS: Total dietary fibre using AOAC methods plus hydrolysis (broad bean pod: 337.3 g kg^?1; pea pod: 472.6 g kg^?1) is higher (P < 0.05) in both by‐products than with the Englyst method (broad bean pod: 309.7 g kg^?1; pea pod: 434.6 g kg^?1). The main monomers are uronic acids, glucose, arabinose and galactose in broad bean pods. However, pea pods are very rich in glucose and xylose. The soluble sugars analysed by high‐performance liquid chromatography in both by‐products have glucose as the most important component, followed by sucrose and fructose. The ferric reducing antioxidant power (broad bean pod: 406.4 µmol Trolox equivalents g^?1; pea pod: 25.9 µmol Trolox equivalents g^?1) and scavenging effect on 2,2‐diphenyl‐1‐picrylhydrazyl radical (EC₅₀ of broad bean pod: 0.4 mg mL^?1; EC₅₀ of pea pod: 16.0 mg mL^?1) were also measured. CONCLUSIONS: Broad bean and pea by‐products are very rich in dietary fibre, particularly insoluble dietary fibre and their extractable polyphenols demonstrate antioxidant activity. Therefore they might be regarded as functional ingredients. Copyright © 2011 Society of Chemical Industry     

The significance of physico chemical properties of plant cell wall materials for the development of innovative food products

Cell wall materials (CWM) are natural constituents of fruits and vegetables. They are added in a growing extent to foods as health ingredients to create innovative products (functional food). CWM or dietary fibres, respectively, have both physiological and technological functional properties, which are considerably modified during the dietary fibre preparation, during the incorporation of the dietary fibre ingredients into foods and generally during processing. Process-dependent external stress and the influence of internal conditions induce changes of the physico-chemical properties of the food constituents (such as particle size and shape, porosity, water binding and structure-forming as well as texturization properties). These changes affect or determine the technological functional, the material and the physiological properties. To evaluate the alterations of structure and properties of plant cell walls during processing without disturbing influences CWM-water-model suspensions and cell wall preparations, carefully dried after a water-ethanol-exchange, can be used. Such model studies and investigations for the improved manufacture of dietary fibre preparations as well as dried fruit and vegetable products show that both the pre-drying treatments (addition of salt, sugar, polysaccharides and surfactants) and the drying step itself considerably influence the extent of shrinkage, cell wall stiffening as well as cell collapse and glass transition. In pre-drying treatments variations of the degree of methoxylation of the pectin component and/or cation charging can be made which cause a pre-formation of structures and/or states of matter that determine essentially the drying process. The ability of rehydration plays an important role for the application and utilization of dried CWM and dietary fibre preparations as well as of dried fruit and vegetable products. The rehydration process is achieved by the plasticizing effect of water, the temperature influence and the external stress, e.g. by stirring, and is supposed to reverse the state transitions, resulting from drying. By application in foods the rehydration of the CWM and dietary fibre preparations can contribute to the formation of texture (texturization). The texturization caused by CWM depends not only on processing and internal conditions but also essentially on the concentration, size, shape, stiffness and deformability of the particles as well as their water binding properties (amount and strength). The investigations show that improved technologies for the production of cell wall and dietary fibre preparations as well as innovative foods with selectively adjusted functional properties require a fundamental understanding of the changes in structure and properties, caused by processing. Furthermore, a well coordinated cooperation of different scientific disciplines using information technology is necessary for a successful development of innovative dietary fibre enriched products.     

Methods for Calculating Dietary Energy Density in a Nationally Representative Sample

There has been a growing interest in examining dietary energy density (ED, kcal/g) as it relates to various health outcomes. Consuming a diet low in ED has been recommended in the 2010 Dietary Guidelines, as well as by other agencies, as a dietary approach for disease prevention. Translating this recommendation into practice; however, is difficult. Currently there is no standardized method for calculating dietary ED; as dietary ED can be calculated with foods alone, or with a combination of foods and beverages. Certain items may be defined as either a food or a beverage (e.g., meal replacement shakes) and require special attention. National survey data are an excellent resource for evaluating factors that are important to dietary ED calculation. The National Health and Nutrition Examination Survey (NHANES) nutrient and food database does not include an ED variable, thus researchers must independently calculate ED. The objective of this study was to provide information that will inform the selection of a standardized ED calculation method by comparing and contrasting methods for ED calculation. The present study evaluates all consumed items and defines foods and beverages based on both USDA food codes and how the item was consumed. Results are presented as mean EDs for the different calculation methods stratified by population demographics (e.g. age, sex). Using United State Department of Agriculture (USDA) food codes in the 2005-2008 NHANES, a standardized method for calculating dietary ED can be derived. This method can then be adapted by other researchers for consistency across studies.     

Colorimetric method for routine measurement of dietary fibre as non-starch polysaccharides. A comparison with gas-liquid chromatography

A method is described for the measurement of dietary fibre as the non-starch polysaccharides in plant material. The basic fractionation procedure from a previously validated gas-liquid chromatographic method has been combined with colorimetric measurement of constituent sugars. The method is shown to produce accurate quantitative data by comparison with the previous gas-liquid chromatographic procedure. Although detailed qualitative information is not obtained, the method described offers the opportunity to measure soluble and insoluble dietary fibre, without the need for expensive gas-liquid chromatography equipment.