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Division of Nutritional Sciences and Department of Animal Sciences, University of Illinois, Urbana, IL 61801
1 To whom correspondence should be addressed. E-mail: gcfahey{at}uiuc.edu.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • viscosity • dietary fiber • gastric • small intestine • digesta
Dietary fibers possess unique chemical and physical characteristics responsible for eliciting an array of physiological responses. Currently, 2 general classifications of fiber exist, soluble (e.g., gums, pectins) and insoluble (e.g., cellulose, wheat bran, soy hulls) (1). One physicochemical property of fiber, viscosity, is recognized as affecting physiological responses (2). Viscous dietary fibers thicken when mixed with fluids; they include polysaccharides such as gums, pectins, and ß-glucans. The degree of thickening when exposed to fluids depends on the chemical composition and concentration of the polysaccharide (2). Viscous fibers have been associated with alterations in blood glucose and cholesterol concentrations, prolonged gastric emptying, and slower transit time through the small intestine (3).
Because of the large variation in physical, chemical, and physiological characteristics of fiber sources, it was suggested that viscosity could serve as an alternative way of classifying soluble fiber (4). Although research has been conducted to address the effects of viscous fibers on physiological responses, few data exist on viscous characteristics of individual fiber sources in relation to one another. For viscosity to serve as a proxy for soluble fiber, it is essential to have an understanding of individual fiber viscosity characteristics.
The objectives of this study were to quantify the viscosities of select dietary fibers (soluble and insoluble) at various concentrations in solution and to determine the effects of altering shear rate on the viscosity of these solutions. A second objective was to determine the effects of fiber source, incubation time, and shear rate on the viscosity of solutions in a two-stage in vitro digestion simulation model.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Experiment 1. All fibrous substrates were analyzed for dry matter (DM),2 organic matter (OM), and crude protein (CP) (5). Total dietary fiber (TDF) and insoluble dietary fiber (IDF) were analyzed according to AOAC methodology (5). Soluble dietary fiber (SDF) was calculated as TDF minus IDF (1,6). All chemical analyses were conducted in duplicate, and values were required to be within 5% of each other; otherwise, the analysis was repeated.
The viscosity of solutions was measured at room temperature (23°C). Before measurement, samples were gently mixed for 30 s before removal of a 2-mL aliquot. Viscosity was measured using a Brookfield digital viscometer (LV-DV-II+) with a Wells/Brookfield cone and plate extension. Solutions containing corn bran, both methylcelluloses, oat bran, both rice brans, soy hulls, wheat bran, and wood cellulose were assayed using a CP-41 cone and plate. A Brookfield LV spindle set (LV-2; LV-3) was used for gel-forming substrates (psyllium, guar gum, and xanthan gum). In this case, solutions were placed in 100-mL glass beakers with a 5-cm diameter. Two viscometer geometries were utilized due to differences in solution consistency. Solutions containing soluble gel-forming substrates were too viscous to pipette and utilize the cone and plate extension. Because these substrates were soluble and dissolved into a gel, cylindrical spindles could be immersed into the gels. On the other hand, insoluble fibers fall out of solution, making measurement with spindles difficult and reducing the accuracy of the viscosity measurement. Although 2 viscometer geometries were used, both were assayed using the same rotational viscometer, calibrated for both geometries. The cone and plate geometry assays a viscosity range of 0.6 to 11,000 cP, whereas spindle geometry assays viscosity ranging from 50 to 400,000 cP. Because the solutions were expected to be non-Newtonian and demonstrate shear-thinning behavior, each solution was assayed across a range of shear rates to obtain a minimum of 3 viscosity values for each solution. Viscosity values were assayed in triplicate.
Experiment 2. For the in vitro digestion simulation, cellulose, guar gum, oat bran, psyllium, rice bran, and wheat bran were used. Substrates were weighed (0.5 g) in duplicate in 50-mL plastic centrifuge tubes. Gastric simulation began with the addition of 5 mL of 0.2 mol/L HCl, 0.5 mL of 10% pepsin:HCl (wt:v), and 12.5 mL of 0.1 mol/L phosphate buffer (pH 6). Solutions were adjusted to pH 2 with 0.2 mol/L HCl or 0.6 mol/L NaOH. The tubes were closed with stoppers and incubated for 6 h at 39°C (7,8). One set of substrates was removed from incubation and frozen at –20°C at 0, 2, 4, and 6 h. After the initial 6 h of incubation, small intestinal simulation began in the remaining tubes with the addition of 2.5 mL of 0.6 mol/L NaOH, 5 mL of 0.2 mol/L phosphate buffer (pH 6.8), and 0.5 mL of 5% pancreatin solution (wt:v), with adjustment to pH 6.8 with HCl or NaOH (7,8). Tubes were incubated at 39°C for an additional 18 h. Substrates were removed from incubation and frozen at –20°C at 0, 3, 6, 9, 12, 15, and 18 h from initiation of small intestinal digestion simulation.
During the in vitro digestion simulation, the viscosities of all solutions were measured as in Expt. 1, with the CP-41 geometry, and across speeds of 0.3, 0.6, 1, 1.5, 2, and 3 rpm (shear rates = 0.6, 1, 2, 3, 4, and 6 s–1). Viscosity values across all time points were assayed in triplicate.
Statistical analysis. Viscosity data were analyzed using GraphPad® software (San Diego, CA) and NLREG® software. Area under the curve (AUC) values were calculated using GraphPad software. NLREG was used to develop a working model of the viscosity flow curve data. Pseudoplastic fluids can be adequately represented by the power law equation (y = a·xb) and termed power law fluids (9–12). In the equation, shear stress (y) is a function of the consistency index or constant (a), shear rate (x), and a dimensionless exponent (b) that indicates closeness to Newtonian flow. The exponent will equal 1 for Newtonian fluids and will be <1 for shear-thinning fluids. The constant is a parameter proportional to the viscosity of power law fluids and is represented in units of centipoise (cP). Model development allowed for the estimation of the constant and exponent parameters in the above equation.
In vitro data (Expt. 2) did not meet the criteria of normality tested by the univariate procedure of SAS® (SAS Institute); therefore, data were log-transformed before statistical analysis. Data were analyzed using the Mixed models procedure of SAS. The experimental design was a factorial randomized complete block design with fiber substrate serving as block. The statistical model included the fixed effect of substrate and the random effect of replicate. Treatment least-squares means were compared using the Bonferroni method to control for the probability of any type I error. A probability of P < 0.05 was accepted as significant.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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14% more viscous than the gum xanthan solution. Viscosity AUC values at 2% concentration for psyllium were 60-fold that of the 0.5% concentration, with the greatest increase occurring between 1 and 1.5%.
Solutions containing corn bran were 2-fold greater at 1% concentrations compared with 0.5%; however, there was little change in viscosity AUC among 1, 1.5, and 2% for corn bran solutions. Viscosity AUC for solutions containing wheat bran at 1% concentration were 63-fold that of 0.5% concentrations. Similar to the pattern noted for corn bran, viscosity AUC for solutions containing oat bran at 1% were 3-fold that of solutions at 0.5% concentration. However, similar to the pattern noted for wheat bran, the viscosity of oat bran solutions did not differ at 1.5 and 2%. Viscosity AUC for solutions containing stabilized rice bran at 2% were 8.5-fold that at 0.5%. Solutions containing defatted rice bran at 2% were 134-fold that of the 0.5% concentrations. Similar increases in viscosity AUC between 0.5 and 2% concentrations were evident with soy hulls and cellulose solutions.
Viscosity of simulated gastric digesta. Overall, during gastric digestion simulation, all substrates differed from one another (P < 0.05), with the exception of cellulose and wheat bran, which had similar values for NLREG (P = 0.74) and AUC (P = 0.60) (Tables 4 and 5). Nonlinear regression indicated that at all 4 time points, viscosity was dependent on shear rate, indicated by negative exponent values. Nonsignificant model fit occurred for solutions containing rice bran at 0 and 6 h (Table 4).
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According to nonlinear regression, viscosity constants for solutions containing psyllium were lower at 0 h (P < 0.05) than at the other 3 time points (Table 4). The only difference (P < 0.05) was detected between 0 and 6 h of gastric simulation for AUC values of solutions containing psyllium (Table 5).
Statistics conducted on nonlinear regression viscosity constants for solutions containing cellulose indicated a lower (P < 0.05) constant at 6 than at 4 h (Table 4). The AUC did not differ at any time point during gastric digestion simulation for solutions containing cellulose (Table 5).
Similar to wheat bran, statistical differences were detected with nonlinear regression analysis for solutions containing rice bran (Table 4). At 0 and 6 h, nonlinear regression analysis indicated a nonsignificant model fit; therefore, exponent values were 1. Viscosity AUC increased (P < 0.05) after 2 and 4 h of gastric simulation, respectively. Upon completion of gastric simulation (6 h), the viscosity AUC for rice bran solutions fell drastically (P < 0.05) compared with all other time points (Table 5).
Guar gum solutions had the highest overall nonlinear regression viscosity constant and AUC values, regardless of time point. Analysis of nonlinear regression data detected an increase (P < 0.05) in viscosity between 2 and 4 h of simulation (Table 4). As gastric simulation continued, viscosity AUC for guar gum solutions continued to increase (P < 0.05) at 4 and 6 h, respectively.
Viscosity of simulated small intestinal digesta. Overall, during small intestinal digestion simulation, all substrates were different from one another (P < 0.05), with the exception of cellulose and wheat bran where values were similar for NLREG (P = 0.27) and AUC (P = 0.87) (Table 6 and 7).
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During small intestinal digestion simulation, the viscosity AUC at 9 h was 2.8-fold that of 0 h (P < 0.05) for solutions containing wheat bran (Table 7). A 52% reduction in viscosity AUC occurred between 9 and 12 h; however, this reduction was not significant (P = 0.17). On the other hand, the reduction was detected (P < 0.05) when nonlinear regression constants were analyzed (Table 6).
A single difference was detected between 3 and 6 h (P < 0.05) when small intestinal simulation viscosity AUC values were analyzed for solutions containing psyllium (Table 7).
Cellulose did not affect viscosity of simulated small intestinal solutions at any time point using either method of analysis.
Nonlinear regression detected a nonsignificant model fit for solutions containing rice bran at 9, 15, and 18 h (Table 6). Viscosity AUC fell (P < 0.05) 69, 71, and 82% at 3, 6, and 9 h, respectively, compared with 0 h (Table 7). During the final hours of simulation (15 and 18 h), viscosity AUC was lower (P < 0.05) than at other time points.
During small intestinal digestion simulation of solutions containing guar gum, both nonlinear regression and AUC data analysis detected similar differences. Compared with the 9-h peak, viscosity AUC for guar gum solutions was lowest (P < 0.05) at the conclusion of small intestinal digestion.
With the exception of wheat bran, all fiber substrates had lower viscosity values (nonlinear regression constants and AUC) at the conclusion of small intestinal digestion than at the initiation of digestion. The largest reduction in viscosity AUC (83%) occurred with solutions containing rice bran. Solutions containing guar gum, oat bran, cellulose, and psyllium were reduced 36, 22, 16, and 15%, respectively, between the initiation and conclusion of digestion.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Pseudoplastic fluids can be described using the power law equation to calculate a consistency index or constant that is proportional to viscosity. Nonlinear regression analysis indicated that all solutions evaluated were non-Newtonian and exhibited shear-thinning behavior as indicated by the negative exponents. This dependency on shear rate was expected and is typical of non-Newtonian fluids exhibiting shear-thinning (pseudoplastic) behavior, or a reduction in viscosity with increasing shear rate (or) rpm (10–12).
Calculation of AUC and nonlinear regression analysis allowed not only for the interpretation of entire flow profiles or flow curve characteristics of the solutions but also for simplified single-number presentations of data and statistical comparisons of data using both methods. Although both methods tended to detect similar statistical differences, nonlinear regression analysis was slightly more sensitive. In addition, AUC accounts only for the area below the established curve, whereas nonlinear regression analysis provides information about the characteristics of the curve itself based on the exponent values calculated. As the exponent value approaches 1, the solutions become less dependent on shear rate and exhibit a more Newtonian characteristic. The larger negative numbers indicate a significant dependence on shear rate, as noted for the majority of solutions in the current study.
At a constant temperature, there is typically a nonlinear increase in viscosity as the concentration of polysaccharide in solution increases; therefore, it was expected that viscosity of all substrate solutions would increase with increasing concentration. Ellis et al. (13) fed growing pigs semipurified diets containing 0, 20, or 40 g guar gum/kg diet and observed an increase in jejunal digesta viscosity, strongly dependent on guar gum concentration in the diet. Compared with controls, the pigs fed 20 and 40 g guar gum/kg diet had 28- and 93-fold increases (P < 0.05), respectively, in viscosity of digesta 60 min after feeding. In addition, Danielson et al. (14) fed rats barley milled fraction shorts (barley tempered to 10% moisture for 12 h followed by milling in an 8-roller dry mill) containing 8.4% ß-glucan at concentrations of 0 (control), 30, 60, or 90% of the diet for 21 d. Digesta viscosity increased (P < 0.05) from 0.2 (control) to 1.9 cP (90% shorts), and was associated with a reduction (P < 0.05) in liver cholesterol (from 12.4 to 3.8 mol/g for control and 90% shorts treatments, respectively). The viscosity of polysaccharides in aqueous solutions will develop as a result of interpenetration of individual chains or coils to form entangled networks. The extent of entanglement and resultant viscosity is determined by the concentration of polysaccharide in solution or the number of chains or coils present (15).
The largest increase in viscosity AUC occurred with Ticacel-43, a high-molecular-weight methylcellulose containing a very high concentration of SDF (92%). It was expected that this substrate would hydrate rapidly and form a gel. Although Ticacel-42 also contained high concentrations of SDF (92.5%), a lower viscosity was attained in a 2% solution. These 2 substrates are low-viscosity (Ticacel-42) and high-viscosity (Ticacel-43) methylcelluloses used as additives in food preparations to control viscosity of products during processing stages. Molecular weight differences likely contributed to the variation in viscosity AUC between Ticacel-42 and Ticacel-43.
An increase in the consumption of dietary fiber will likely contribute to an increase in the viscosity of gastrointestinal contents. Although substrates containing high concentrations of SDF (methylcellulose, guar gum, and gum xanthan) resulted in very high viscosities, other fibers such as psyllium, oat bran, and soy hulls also were effective in achieving higher viscosity values in 2% solutions. It is unclear, however, whether physiological responses such as reduced blood glucose and blood lipids associated with ingestion of viscous fibers are dependent on dietary concentration of viscous fiber.
The initial increase in viscosity during simulated gastric digestion may have been a response to hydration of the fibrous substrates and their interaction with the acidic medium that could release bound nonstarch polysaccharides (NSP). The reductions in simulated gastric viscosity may have resulted from the breakdown of polysaccharide structure with prolonged exposure to acidic conditions. Nonstarch polysaccharide fractions of fiber sources may be released and broken down upon acidification. There may be an optimal pH, dependent on the chemical composition of the fiber source, at which NSP are released, resulting in increased viscosity. Beyond that pH, viscosity may be lost due to the breakdown of NSP (16). The reduction in viscosity was not expected for solutions containing guar gum. Guar gum is a neutral ß 1–4 linked linear polymer of mannose with single D-galactopyranosyl units attached to alternate D-mannopyranosyl units by 
1–6 linkages. This chemical composition is responsible for the neutral characteristic of guar gum and its lack of interaction with the acidic medium (17).
During simulated small intestinal digestion, viscosity increased and peaked between 3 and 12 h, and then dropped by 18 h. During simulated small intestinal digestion, substrates were exposed to solutions that digest proteins and digestible carbohydrates, including starch. The interaction with digestive solutions likely would contribute to structural interactions with fluid that would result in increased viscosity as noted during the early and middle stages of digestion. As digestion proceeded, polysaccharide structural interactions may have been modified, resulting in lower viscosity values observed at the end of simulated small intestinal digestion.
It was expected that fibrous substrates containing high concentrations of IDF would exhibit the lowest viscosity values during simulated gastric and small intestinal digestion and would not affect viscosity over time. Insoluble dietary fibers typically have lower water-holding capacity than SDF; however, many fibers such as wheat bran contain water-soluble arabinoxylans that contribute to water-holding capacity and increased viscosity in solutions (18). Maziya-Dixon and Klopfenstein (19) measured the viscosity of diet slurries containing oat bran, wheat brans (2), wheat flours (4), and cellulose. Diet slurry viscosity was highest for oat bran (240 cP) followed by the 2 wheat brans (120 cP) and wheat flours (70–100 cP). Diet slurries containing cellulose had the lowest viscosity (60 cP). In the current study, oat bran also resulted in higher solution viscosity compared with wheat bran or cellulose. Oat bran has been studied extensively because of its effects on physiological responses such as the attenuation of blood glucose. The major component that contributes to the viscosity characteristics of oat bran solutions is the concentration of ß-glucan. This highly viscous polysaccharide is present in rolled oats but reaches a concentration of 15% in oat bran (20).
Although psyllium contains a very high concentration of IDF (82.6%), viscosity values for gastric and small intestinal solutions were very high during digestion simulations. Even with a high concentration of IDF present, psyllium has an extraordinary gel-forming characteristic that results in a very viscous solution upon hydration. Psyllium has been studied extensively for its physiological responses such as blood lipid profile attenuation and laxation. Three fiber fractions are associated with the unique properties of psyllium. According to Marlett and Fischer (21), fraction A is alkali insoluble and not fermented by microbiota in the colon, whereas fraction B, constituting 55% of the psyllium, is poorly fermented and is associated with increased stool moisture and fecal bile acid excretion. Fraction C is highly viscous and rapidly fermented by colonic microbiota. The gel-forming polysaccharide in psyllium is a highly branched arabinoxylan consisting of a xylose backbone and arabinose- and xylose-containing side chains. The arabinoxylans in psyllium are not fermented as they are in many cereal grains (21).
Viscosity values for solutions containing guar gum were very high during gastric digestion simulation. Guar gum is a very soluble galactomannan derived from the Indian cluster bean. Once guar gum is fully hydrated, thick solutions and gels are formed rapidly. Guar gum is a neutral polysaccharide; therefore, no differences were expected due to exposure to acidic conditions during gastric simulation (17). The viscosity of solutions containing guar gum has been studied extensively, particularly for physiological responses. Jarjis et al. (22) indicated a dependence of concentration on viscosity of guar gum inclusion at 2.5 and 14.5 g, added to a 50-g glucose solution consumed by healthy adult humans. In addition, Gallaher and Schaubert (23) fed rats diets containing 8% guar gum. After diet acclimation, rats were injected with streptozotocin (40 mg/kg body weight) to induce a diabetic response. The rats were killed after 28 d of treatment. The viscosity of the small intestinal contents increased from 2 to 1147 cP in rats fed control (cellulose) and guar gum diets, respectively. The percentage of glycated hemoglobin was reduced (P < 0.05) from 19.5 (basal) to 16% in rats fed guar gum diets. Consumption of viscous gums such as guar gum and gum xanthan may elicit beneficial physiological responses (attenuation of post-prandial blood glucose, reduction in plasma cholesterol).
The drawback to in vitro investigations is the inability to account for absorption of digested molecules and water, or secretion of fluid/mucous in the stomach and small intestine. A large proportion of water absorption occurs in the small intestine, as does the majority of macronutrient absorption (24). It is unclear how the removal of digested nutrients and water would affect the resultant viscosity of fluid within the gastrointestinal tract. Further research is warranted to elucidate the effect these processes might have on in vivo viscosity to compare in vitro data with that obtained using in vivo animal models.
In summary, because of the dependence of viscosity on shear rate, it is necessary to assay non-Newtonian solutions at multiple shear rates to establish the entire viscosity profile of such solutions. In the current study, the presentation of viscosity data as AUC values or as parameters calculated through nonlinear regression analysis resulted in similar representations of the viscous characteristics of the solutions. Although similarities in the 2 methods were noted, presentation of parameters from nonlinear regression analysis provides additional information regarding flow properties of solutions that had previously been overlooked in studies presenting only 1 viscosity value.
Cellulose, rice bran, and wheat bran did not increase the viscosity of simulated stomach and small intestinal contents. These insoluble dietary fibers do not appear to play a significant role in the production of viscosity in the gastrointestinal tract. Therefore, their inclusion in diets may be most beneficial for laxation, rather than physiological responses associated with viscosity such as blood glucose attenuation. On the other hand, solutions containing guar gum and psyllium were very viscous during gastric and small intestinal simulations. Oat bran was intermediate in viscosity characteristics. Consumption of oat bran, psyllium, and guar gum may affect physiological responses such as postprandial blood glucose and blood lipid concentrations.
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FOOTNOTES |
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Manuscript received 25 September 2005. Initial review completed 1 November 2005. Revision accepted 25 January 2006.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Prosky L, Asp NG, Schweizer TG. DrVries JW, Furday I. Determination of insoluble and soluble fiber in food and food products: collaborative study. J Assoc Off Anal Chem. 1992;75:360–6.
2. Schneeman BO. Dietary fiber and gastrointestinal function. In: McCleary BV, Prosky L, editors. Advanced dietary fiber technology. Ames (IA): Blackwell Sciences; 2001.p. 168–76.
3. Mälkki A. Physical properties of dietary fiber as keys to physiological functions. Cereal Foods World. 2001;46:196–9.
4. Institute of Medicine. Dietary reference intakes: proposed definition of dietary fiber. Washington (DC): National Academy Press; 2001.
5. Association of Official Analytical Chemists. Official methods of analysis. 17th ed. Washington (DC): AOAC; 2002.
6. Prosky L, Asp NG, Furda I, DeVries JW, Schweizer TG, Harland BF. Determination of total dietary fiber in foods and food products: Collaborative study. J Assoc Off Anal Chem. 1984;67:1044–52.
7. Boisen S. A model for feed evaluation based on in vitro digestible dry matter and protein. In: Fuller MF, editor. In vitro digestion for pigs and poultry. New York (NY): Commonwealth Agriculture Bureau International (CABI) Publishing; 1991.
8. Boisen S, Eggum BO. Critical evaluation of in vitro methods for estimating digestibility in simple-stomach animals. Nutr Res Rev. 1991;4:141–62.
9. Fox RW, McDonald AT, Pritchard PJ. Fundamental concepts. In: Fox RW, McDonald AT, Pritchard PJ, editors. Introduction to fluid mechanics. 6th ed. Hoboken (NJ): Wiley & Sons; 2004. p. 26–43.
10. Takahashi T, Sakata T. Large particles increase viscosity and yield stress of pig cecal contents without changing basic viscoelastic properties. J Nutr. 2002;132:1026–30.
11. Bourne M., editor. Food texture and viscosity: concept and measurement. 2nd ed. San Diego (CA): Academic Press; 2002.
12. Reppas C, Meyer JH, Sirois PJ, Dressman JB. Effect of hydroxypropylmethylcellulose on gastrointestinal transit and luminal viscosity in dogs. Gastroenterology 1991;100:1217–23.[Medline]
13. Ellis PR, Roberts FG, Low AG, Morgan LM. The effect of high-molecular weight guar gum on net apparent glucose absorption and net apparent insulin and gastric inhibitory polypeptide production in the growing pig: Relationship to rheological changes in jejunal digesta. Br J Nutr. 1995;74:539–56.[Medline]
14. Danielson AD, Newman RK, Newman CW, Berardinelli JG. Lipid levels and digesta viscosity of rats fed a high-fiber barley milling fraction. Nutr Res. 1997;17:515–22.
15. Ellis PR, Dawoud FM. Blood glucose, plasma insulin and sensory responses to guar-containing wheat breads: effects of molecular weight and particle size of guar gum. Br J Nutr. 1991;66:363–79.[Medline]
16. George J, McCracken KJ. Effects of acid and alkali concentration on in vitro measurement of wheat viscosity. Anim Feed Sci Technol. 2002;98:237–44.
17. Hoad CL, Rayment P, Spiller RC, Marciani L, Celis Alonso B, Traynor C, Mela DJ, Peters HPF, Gowland PA. In vivo imaging of intragastric gelation and its effect on satiety in humans. J Nutr. 2004;134:2293–300.
18. Saulnier L, Peneau N, Thibault JF. Variability in grain extract viscosity and water-soluble arabinoxylan content in wheat. J Cereal Sci. 1995;22:259–64.
19. Maziya-Dixon BB, Klopfenstein CF. Nutritional properties of hard white and hard red winter wheats and oatmeal. I: Effects on cholesterol levels and fecal fat, neutral sterols, and bile acids in cholesterol-fed rats. Cereal Chem. 1994;71:539–43.
20. Wood PJ, Braaten JT, Scott FW, Riedel D, Poste LM. Comparisons of viscous properties of oat and guar gum and the effects of these and oat bran on glycemic index. J Agric Food Chem. 1990;38:753–7.
21. Marlett JA, Fischer MH. The active fraction of psyllium seed husk. Proc Nutr Soc. 2003;62:207–9.[Medline]
22. Jarjis HA, Blackburn NA, Redfern JS, Read NW. The effect of ispaghula husk (Fybogel® and Metamucil®) and guar gum on glucose tolerance in man. Br J Nutr. 1984;51:371–8.[Medline]
23. Gallaher DD, Schaubert DR. The effect of dietary fiber type on glycated hemoglobin and renal hypertrophy in the adult diabetic rat. Nutr Res. 1990;10:1311–23.
24. Groff JL, Gropper SS. The digestive system: mechanism for nourishing the body. In: Groff JL, Gropper SS, editors. Advanced nutrition and human metabolism. 3rd ed. Belmont (CA): Wadsworth Thomson Learning; 2000. p. 24–52.
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