Dietary fibre fractions in cereal foods measured by a new integrated AOAC method

The reliable determination of soluble, insoluble and total dietary fibre in baked goods and cereal flours is an important issue for research, nutritional labelling and marketing. We compared total dietary fibre (TDF) contents of selected cereal based foods determined by AOAC Method 991.43 and the new AOAC Method 2009.01. Fifteen bread and bakery products were included in the study. Our results showed that TDF values of cereal products determined by AOAC Method 2009.01 were always significantly higher than those determined by AOAC Method 991.43. This was explained by the inclusion of low molecular weight soluble fibre fractions and resistant starch fractions in the TDF measurement by AOAC 2009.01. This documents that nutritional labelling of cereal products poses the challenge how to update TDF data in nutrient databases in a reasonable time with an acceptable expenditure.     

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.     

In vitro Digestibility of Hydroxypropylated and Cross-linked Waxy and Non-waxy Rice Starches

In vitro digestibility of hydroxypropylated and cross-linked waxy and non-waxy rice starches was investigated to find the proper resistant starch (RS) assaying method for chemically modified starches. RS and total dietary fiber (TDF) content of hydroxypropylated and cross-linked waxy and non-waxy rice starches were measured using the approved AOAC RS assay procedure (AOAC method 2002.02) and the AOAC TDF assay procedure (AOAC method 985.29). Hydroxypropylation did not alter the RS content of waxy and non-waxy rice starches (less than 1% of RS). Cross-linking also did not change the RS content of waxy and non-waxy rice starches (less than 1% of RS). It is interesting to note that non-RS content decreased with increasing hydroxypropylation (97-80%) and cross-linking (99-95%) in both waxy and non-waxy rice starches. This indicates that some fraction of RS in hydroxypropylated and cross-linked waxy and non-waxy rice starches cannot be measured using approved AOAC RS and TDF assay procedures. Therefore, the RS and TDF assay procedures performed in this study are not appropriate to determine the RS content of chemically modified starch. Further investigation is needed to develop a method to determine the RS content of chemically modified starch.     

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.

     

Iron absorption from meat and meat products: Part 2-Iron absorption from high-roughage meat products

The main reasons for the inhibiting effect of dietary fibre on meat iron absorption in the intestine are examined. A model experiment estimates binding of iron by the dietary fibre (DF) of wheat bran. A radioactive tracer method was applied to volunteers to detect the availability of iron from fibrous meat foods. The evidence suggests that incorporating up to 2% of dietary fibre into meat products reduces iron absorption factors by no more than 1-2%. Adding ascorbic acid in the presence of DF lowers them only by 0·1-0·5%, i.e. it does not damage iron absorption processes.     

Chemical composition of olive by-product and modifications through enzymatic treatments

The purpose of the present work was to study the dietary fibre (DF) fraction of olive cake and modify the fibre structure through enzymatic treatments in order to improve the sensory quality of this by-product for its incorporation into a baked product. Two different commercial enzyme preparations were used for enzymatic modifications: Viscozyme L, a hemecellulase/cellulase multi-enzyme complex, and Olivex which contains different pectolitic main activities as well as various side activities, hemicellulases and cellulases. DF consists of 800 g total dietary fibre per kg dry matter. More than 91% of the DF are insoluble and the monosaccharide composition of this fraction indicates the presence of mainly cellulose and xyloglucans or xylans. Approximately 75% of the uronic acids found in olive cake are associated to the insoluble DF (IDF). Arabinans and uronic acids polysaccharides are the major fibre components in the soluble DF (SDF) fraction. Enzymatic treatments with commercial preparations caused changes in the DF content and in the IDF:SDF ratio depending on enzyme concentrations and incubation time. Baking experiments showed that a substitution of 10% of wheat flour by enzymatically modified olive cake led to an improved texture compared to products containing untreated cake.     

Modification of physiochemical properties of copra meal by dilute acid hydrolysis

Coconut residue or copra meal (CM), a by‐product after pressing cream and oil out of the coconut meat, is a good source of dietary fibre (DF), but high water‐holding capacity (WHC) of CM limits the quantity of fibre incorporated into food products. This study focused on the modification of CM physiochemical properties using acid hydrolysis to improve its potential utilisation as source of food fibres or low‐calories bulk ingredients in food applications. Acid hydrolysis using 0.5% HCl significantly reduced swelling capacity (SC) and water retention capacity, whereas bulk density (BD) and soluble DF content of the modified CM significantly increased. Monosaccharide composition profile, gel penetration profile and FT‐IR spectra indicated the destruction of CM matrix structure. This destruction increased compactness of the structure and lessened the ability of CM to hold water. Substituting the modified CM for wheat flour in bread and cookies significantly improved bread and cookies qualities compared with the use of the untreated CM. Response surface methodology showed that HCl concentration, hydrolysis temperature and time influenced properties of the modified CM. The models predicting their relationships were also generated.     

Characterisation of dietary fibre components in rye products

In this study, dietary fibre (DF) was characterised in rye products from a local supermarket. Soft breads generally had lower DF contents (8–18%) than had crisp breads (13–20%) due to high inclusion of wheat flour. For some products, the labelled DF values contained fructan, but others did not. However, for most products, the DF values analysed exceeded those declared. Arabinoxylan (AX) and fructan were generally the main DF components in the products, followed by cellulose and resistant starch, β-glucan, Klason lignin and arabinogalactan. In the soft breads, cellulose and resistant starch concentrations were relatively high, due to significant formation of resistant starch. During bread manufacturing, the molecular weight of β-glucan was highly degraded, while that of AX was more resistant. Extruded products had the highest β-glucan extractability and the extracted β-glucan retained its molecular weight most, which may be of nutritional significance. In rye milling fractions, about 50% of the fructan content analysed had a degree of polymerisation below 10, i.e. it comprised oligosaccharides. The crisp breads produced without yeast had the highest DF and fructan contents and the highest proportion of low-molecular weight fructan. These results indicate that, during bread-making, the low-molecular weight fraction of fructan was most available for degradation by yeast or by endogenous enzymes present in the ingredients.     

Development of high-fruit-dietary-fibre muffins

 Following medical recommendations, consumers now demand fibre-fortified food products. The aim of this study was to develop muffins in which peach dietary fibre (DF) was added at 2, 3, 4, 5 or 10% levels, substituting up to 32% flour. The products were compared to a control muffin (100% flour). It was observed that the moisture of the muffins increased with the DF content because of the high water-holding capacity of peach DF. Weight (30±2 g), height (4.5±0.4 cm), springiness (0.88±0.07 cm) and cohesiveness (0.46±0.04) were not affected by DF content, but the rest of the textural parameters (hardness, chewiness and gumminess) increased with DF content. The incorporation of this ingredient produced slightly darker products. Muffins with 2, 3, 4 and 5% peach DF levels were considered to be as acceptable as the control, based on hedonic-scale ratings given by consumer panellists. Received: 10 February 1999 / Revised version: 6 April 1999     

水溶性膳食纤维聚葡萄糖含量检测方法的进展

新型水溶性膳食纤维聚葡萄糖不能被测定总膳食纤维(TDF)的AOAC方法985.29定量测定,从而影响了其推广应用。本文简要介绍了聚葡萄糖的结构特点,详细讨论了聚葡萄糖含量检测方法的沿革,并详细介绍了FCC方法和最新的能够把聚葡萄糖作为纤维测定的AOAC方法2000.11。     

Heat-moisture treatment of high-amylose corn starch increases dietary fiber content and lowers plasma cholesterol in ovariectomized rats

ABSTRACT:  The effect of dietary high-amylose corn starch (HACS) of varying dietary fiber (DF) content on plasma cholesterol was examined in ovariectomized (OVX) rats. Gelatinized normal corn starch (G-CS) was used as a reference. OVX rats were fed a fiber-free purified diet containing G-CS, HACS, gelatinized high-amylose corn starch (G-HACS), or heat-moisture treated HACS (HM-HACS) at 400 g starch/kg diet for 21 d. The DF content of G-CS, HACS, G-HACS, and HM-HACS measured by the AOAC method was 0.1, 19.3, 2.4, and 64.5 g/100 g, respectively. The dry weight of cecal contents, cecal wall weight, the amount of short chain fatty acids in cecal contents, the amount of bile acids in small intestinal contents, and fecal excretion of neutral sterols increased logarithmically with increasing DF, while total plasma cholesterol concentration decreased. On the other hand, hepatic CYP7A1 activity, fecal dry weight, and fecal excretion of bile acids increased linearly with increasing DF, while body weight gain decreased. The hypocholesterolemic effect of HACS in OVX-rats appeared to be more effective by heat-moisture treatment.     

Application of common wheat bran for the industrial production of high‐fibre pasta

The study was conducted on the effect of the addition of common wheat bran on the chemical composition, physical properties, cooking quality and sensory traits of durum wheat pasta. The pasta was produced on an industrial scale, applying an addition of common wheat bran at doses ranging from 20 to 40%. The products obtained were compared to the pasta from whole‐grain durum wheat flour, produced under identical conditions and with commercially available whole‐grain durum wheat pasta. The increase in the content of wheat bran in the pasta caused a significant increase (Duncan test, P ≤ 0.05) of the content of protein, lipids, ash and total dietary fibre (TDF). The application of 25–30% addition of common wheat bran allowed obtaining the products which are as rich in dietary fibre as the pasta prepared at the same technological parameters from whole‐grain durum flour. The pasta containing up to 30% of bran was characterised with lower losses of dry mass and higher resistance to overcooking, in comparison with the pasta made of whole‐grain durum. Simultaneously, the products had very good sensory quality.     

Nutritional and functional added value of oat, Kamut, spelt, rye and buckwheat versus common wheat in breadmaking

BACKGROUND: Multicereal/pseudocereal blends based on major and minor seeds with high nutritional profile appear as a promising strategy, hardly explored, to obtain enhanced value grain‐based foods such as bread. RESULTS: In a preliminary stage the suitability of minor/ancient cereals (rye, oat, Kamut^® wheat, spelt wheat) and pseudocereals (buckwheat) was assessed in single (100% of wheat flour replacement) and multigrain (from 20 to 44% of wheat flour replacement) matrices. The research allowed identification of the qualitative (oat, rye, buckwheat) and quantitative (up to 75% of wheat flour replacement) grains in the mixed matrices providing enhancement of nutritional quality (higher protein content, higher mineral content, lower digestible starch, higher viscous fibre content, higher resistant starch content, source of antioxidants) and minimisation of techno‐functional impairment and sensory depreciation of the resulting breads. CONCLUSION: The quality profile of associated mixtures of oat, rye, buckwheat and common wheat flours (20:20:20:40 w/w/w/w) endorsed the proposed grain blend as suitable to make highly nutritious, modern and innovative baked goods meeting functional and sensory standards in terms of nutritional added value (improved dietary fibre fractions, minerals and antioxidant activity, slower starch hydrolysis), palatability (high sensory scores), convenience (extended keepability during storage) and easy handling during processing. Copyright © 2011 Society of Chemical Industry     

Effect of Condensed Tannins in the Analysis of Dietary Fiber in Carob Pods

Insoluble and soluble dietary fiber (IDF and SDF) determined gravimetrically from ripe carob pods after enzymatic treatments, were 32.6% and 6.8%, on dry matter basis. About 50% of the weight of the DF residues corresponded to tannins and protein, because of protease inhibition, and protein-tannin complexes prevented the removal of these constituents in carobs. Nonstarch polysaccharides (14.7% dry weight) and composition were determined by GLC analysis in acid hydroly-sates of samples. The results were discussed showing that the content of DF obtained by enzymatic procedures, including the suggested AOAC method, may be overestimated because of the presence of condensed tannins.     

Pasting properties of starch and protein in selected cereals and quality of their food products

In an attempt to improve intake of dietary fibre and antioxidants and quality of whole grain products, whole grain meals from barley, millet, rye and sorghum were evaluated individually and in blends with wheat flour in terms of starch pasting properties and protein heat damage, during cycles of heating and cooling in RVA tests. The whole grain meals were blended with either hard or soft wheat flour and processed into bread, cake, cookie or snack products. The products were then evaluated with regard to physical properties and acceptability. Significant differences were observed between cereals in starch peak, breakdown and setback viscosities as well as in protein peak viscosity. The results showed that RVA could be used to help formulate cereal blends with certain pasting properties. Substitution of wheat flour, with 15% of barley, rye, millet or sorghum whole grain, did not have significant detrimental effects on physical properties or acceptability of pita bread. Additionally, replacement of wheat flour with up to 30% of barley, rye, millet or sorghum whole grain meal had no significant effects on quality of cakes or cookies. A multigrain snack-like food was also developed as a healthy product and was highly acceptable in a sensory test. The developed product would help enhance consumption of whole grain foods, resulting in improved intake of fibre and health-enhancing components.     

Dietary Fibre Content and Composition of Some Edible Fungi Determined by Two Methods of Analysis

Six common edible fungi from four orders of Basidiomycetes, namely Agaricus bisporus (Agaricales), Auricularia auricula and Auricularia polytricha (Auriculariales), Tremella fuciformis (Tremellates), Ganoderma lucidum and Poria cocos (Aphyllophorales), were analysed for their total dietary fibre (TDF) content using the Association of Official Analytical Chemists (AOAC) method and for dietary fibre content and composition using the Uppsala method. The non-protein nitrogen contributed from fungal chitin was corrected in the fibre residue obtained by the AOAC method. The TDF content measured by the AOAC method was always greater than that of the Uppsala method. The TDF content determined by the AOAC and Uppsala methods ranged from 182 and 132 g kg^-1 (dry matter) in A bisporus to 735 and 711 g kg^-1 (dry matter) in P cocos, respectively. Neutral and amino sugars were the dominant sugars in all the fungi. Sugar composition of the TDF reflected that the major cell wall polysaccharides in most fungi were hemicelluloses, such as β-glucan and glucuronoxylomannan, pectic substances and chitin. Judging from their high fibre content and unique fibre composition, edible fungi have considerable value as sources of dietary fibre in human nutrition. © 1997 SCI.     

Technologies for enhancement of bioactive components and potential health benefits of cereal and cereal-based foods: Research advances and application challenges

Cereal grains are a major source of human food and their production has steadily been increased during the last several decades to meet the demand of our increasing world population. The modernized society and the expansion of the cereal food industry created a need for highly efficient processing technologies, especially flour production. Earlier scientific research efforts have led to the invention of the modern steel roller mill, and the refined flour of wheat has become a basic component in most of cereal-based foods such as breads and pastries because of the unique functionality of wheat protein. On the other hand, epidemiological studies have found that consumption of whole cereal grains was health beneficial. The health benefit of whole cereal grain is attributed to the combined effects of micronutrients, phytochemicals, and dietary fibre, which are mainly located in the outer bran layer and the germ. However, the removal of bran and germ from cereal grains during polishing and milling results in refined flour and food products with lower bioactive compounds and dietary fibre contents than those from whole grain. Also, the level of bioactive compounds in cereal food is influenced by other food preparation procedures such as baking, cooking, extrusion, and puffing. Therefore, food scientists and nutritionists are searching for strategies and processing technologies to enhance the content and bioavailability of nutrients, bioactive compounds, and dietary fibre of cereal foods. The objective of this article was to review the research advances on technologies for the enhancement of bioactive compounds and dietary fibre contents of cereal and cereal-based foods. Bioactivities or biological effects of enhanced cereal and cereal-based foods are presented. Challenges facing the application of the proposed technologies in the food industry are also discussed.     

Simplified methods for the preparation and analysis of dietary fibre

A critical study was made of the various factors which affect the quantitative removal of starch, by enzymic methods, from starch-rich products; the products examined include potatoes, potato powder, oats and rye biscuit. Disruption of product by ball-milling in aqueous ethanol, followed by gelatinisation, are essential to give maximum enzyme accessibility as shown by light microscopy and analytical studies. The enzyme preparations were checked for the presence of contaminating β-glucanase activity using suitable substrates. The recommended method for the removal of starch involves treatment with either a mixture of human salivary α-amylase and pullulanase or amyloglucosidase; the first method was found to be slightly better. Based on these studies simplified methods for the preparation of dietary fibre (DF) have been formulated. The neutral sugars released from the DF on 1m H₂SO₄- or Saeman-hydrolysis were estimated by the alditol acetate procedure, and a modified carbazole method has been used for the estimation of total uronic acid in the fibre. A set of determinations which gives an estimate of the main types of DF polymers, including the enzymically non-degradable starch of processed products, is given. Although the method is not suitable for preparing gram-quantities of relatively pure DF, it can be used for screening a range of products. Some of the problems associated with the use of Van Soest neutral detergent fibre for estimating DF content of food products are also described.     

Characterisation of peach dietary fibre concentrate as a food ingredient

Insoluble and soluble dietary fibre (DF) fractions of peach DF concentrate, obtained by an enzymatic-chemical method, were analysed for neutral sugars, uronic acids and Klason lignin. Proximate composition, energy value, colour and water- and oil-holding capacities were also determined. Total DF constituted 31–36% dry matter (DM) of the concentrate and insoluble DF was its major fraction (20–24% DM). The high proportion of soluble fraction (11–12% DM) in the peach DF concentrate, in comparison with cereal brans, was noticeable. Insoluble and total dietary fibre contents significantly decreased throughout the harvest time of the original fresh fruit. Results suggested that peach DF concentrate may be not only an excellent DF source but an ingredient in the food industry because it showed a high affinity for water (9.12–12.09 g water/g fibre) and low energy (3.723–3.494 kcal/g). However, the use of this material could affect the colour and pH of the final product.     

Rye bread reduces plasma cholesterol levels in hypercholesterolaemic pigs when compared to wheat at similar dietary fibre level

BACKGROUND: Rye is a whole‐grain cereal with the potential of contributing to a healthy diet, but research on rye in relation to chronic diseases is scarce compared to wheat and oats. In this study, a total of 17 hypercholesterolaemic pigs were fed high‐fat high‐cholesterol rye (n = 9) or wheat‐based buns (n = 8) with similar dietary fibre (DF) content for 9–10 weeks to study the effect on cardiovascular risk factors. RESULTS: Ingestion of rye bread resulted in a 40% lower plasma total and LDL cholesterol compared to the wheat group, whereas HDL cholesterol, insulin and glucose concentrations were not affected by dietary treatments. Intestinal viscosity was 7.2 times higher, and organic matter and fat digestibility significantly reduced in the pigs fed rye buns. The hepatic expression of the cholesterol 7α‐hydroxylase gene (CYP7A1) was lower in rye‐fed pigs, whereas four other key genes involved in cholesterol metabolism were not affected. Plasma cholesterol correlated inversely with intestinal viscosity and organic matter digestibility. CONCLUSION: The ability of DF from rye to interfere with digestion and absorption is more important for whole‐body cholesterol homeostasis than regulation in the liver at gene level. Copyright © 2008 Society of Chemical Industry