24

5

Research ArticleReceived: 5 April 2007 Revised: 15 July 2008 Accepted: 8 September 2008 Published online in Wiley Interscience: 31 October 2008

(www.interscience.com) DOI 10.1002/jsfa.3433

Water-holding capacity of insoluble fibredecreases free water and elevates digestaviscosity in the ratToru Takahashi,a∗ Yukio Furuichi,b Takafumi Mizuno,b Masako Kato,a

Aya Tabara,a Yuka Kawada,a Yoshiyuki Hirano,c Kin-ya Kubo,d

Minoru Onozukac and Osamu Kuritae

Abstract

BACKGROUND: The relationships between possible physiological properties of insoluble fibre and the viscosity of digestaare poorly understood. The aim of this study was to investigate the effect of insoluble fibres with different water-holdingcapacity, swelling, oil-holding capacity and cation exchange capacity on gastric, small intestinal and caecal contents in rats feda semi-purified diet containing either no fibre (control), 50 g kg−1 tossa jute fibre or 50 g kg−1 shiitake fibre.

RESULTS: The water-holding capacity, swelling, oil-holding capacity and cation exchange capacity of insoluble fibres of tossajute were higher than those of shiitake (P < 0.001). The order of the viscosities of digesta was control group < shiitake fibregroup < tossa jute fibre group in gastric, small intestinal and caecal contents (P < 0.05). The digesta viscosity at a shear rate of40 s−1 was strongly correlated with the free water content of digesta (r = −0.89; P < 0.01). The free water content of digestadepended on the water-holding capacity of insoluble fibres represented as a linear function with negative slope (P < 0.001).

CONCLUSION: The viscosity of digesta depends on the free water content, and this is reduced by fibre that holds water and canswell.c© 2008 Society of Chemical Industry

Keywords: insoluble fibres; viscosity; water-holding capacity; free water; digesta; rat

INTRODUCTIONInsoluble fibres such as crystalline cellulose increase the viscosityof digesta by supplying solid particles,1 – 3 which in turn makeit more difficult for nutrients to move in the lumen to reachthe absorptive surface4 and reduce postprandial blood glucoseincrements.5 Thus digesta viscosity is an important factor fordigestion6 and absorption of nutrients.4 While particle size andlevel of insoluble fibres are correlated positively with digestaviscosity,1 the effects of other physicochemical properties ofinsoluble fibres on digesta viscosity remain unclear. The purpose ofthis study was to determine whether physicochemical propertiessuch as water-holding capacity, swelling, oil-holding capacity andcation exchange capacity of insoluble fibres could affect digestaviscosity. Insoluble fibres were prepared using alkali- and acid-insoluble fractionation with or without phosphorylation.7 Thephysiological role of insoluble fibres with high water-holdingcapacity and swelling is also discussed.

METHODSInsoluble fibre sourcesInsoluble fibres were extracted from tossa jute (Corchorus olitorius)and shiitake (Lentinus edodes). Tossa jute is a vegetable whoseleaves and tender shoots are commonly eaten in Egypt, India

and Japan. Shiitake is a type of mushroom used in Chinese andJapanese dishes. Insoluble fibres of tossa jute and shiitake consistmainly of cellulose and chitin respectively.

Dry powdered leaves of tossa jute were purchased fromMoroheiya Production’s Cooperative Association of Iga (Mie,Japan). Dry powders of shiitake were provided by Yumekouboof Suzuka Sanroku (Mie, Japan).

∗ Correspondence to: Toru Takahashi, Graduate School of Human Life Science,Mimasaka University, 50 Kitazono, Tsuyama, Okayama 708-8511, Japan.E-mail: takahashitoru71@nifty.com

a Faculty of Human Life Science, Mimasaka University, 50 Kitazono, Tsuyama,Okayama 708 8511, Japan

b FacultyofBioresources,MieUniversity,1577Kurimamachiya,Tsu,Mie514-8507,Japan

c Department of Physiology and Neuroscience, Kanagawa Dental College,Yokosuka 238-8580, Japan

d Division of Oral Structure, Function and Development, Asahi University Schoolof Dentistry, 1851 Hozumi, Mizuho, Gifu 501-0296, Japan

e Industrial Research Division, Mie Prefectural Science and Technology PromotionCentre, 5-5-45 Takajaya, Tsu, Mie 514-0819, Japan

J Sci Food Agric 2009; 89: 245–250 www.soci.org c© 2008 Society of Chemical Industry

24

6

www.soci.org T Takahashi et al.

Preparation of insoluble fibresDifferent preparation methods were employed for tossa jutefibre (TF) and shiitake fibre (SF) in order to match the chemicalcomposition of TF with that of SF and give it a different water-holding capacity. TF was prepared by alkali- and acid-insolublefractionation with phosphorylation.7 SF was prepared as anenzymatically fibre-rich fraction7 without phosphorylation. In aprevious study, X-ray diffraction and chemical analysis confirmedthat phosphorylation did not chemically modify the fibres butremoves protein and increases the purity of insoluble fibres in TF.7

Phosphorylation also imparts a high water-holding capacity bycreating elongated conformations of insoluble fibres.7

The enzymatically fibre-rich fractions of SF were prepared asfollows.7 Samples (1 kg dry matter) were digested in 10 L of0.05 mol L−1 HCl (Wako, Osaka, Japan) containing 100 g of pepsinfrom porcine stomach mucosa (Wako). This solution was keptat 37 ◦C for 3 h and then neutralised with NaOH (Wako). Thesolution was subsequently heated for 10 min in a boiling waterbath and incubated in 400 mL of 1 mol L−1 phosphate buffer(pH 7) and 100 g of pancreatin (Wako) with approximately 1 gof thymol crystals (Wako) at 37 ◦C overnight with occasionalstirring. Three volumes of ethanol were added to precipitate thepolysaccharides. The precipitates were collected by centrifugation(7000 × g, 15 min), washed twice with 2 L of distilled water andthen freeze-dried to constant weight.

The alkali- and acid-insoluble fractions (with phosphorylation)of TF were prepared as follows.7 Samples (100 g dry matter)were incubated in 1.5 L of 0.25 mol L−1 NaOH containing 10 g ofsodium metaphosphate, 0.2 g of sodium polyphosphate and 10 gof sodium sulfate at 50 ◦C for 2 h. The precipitates of insolublefractions were washed once with 1 L of 0.25 mol L−1 NaOH bycentrifugation (7000 × g, 15 min). The precipitates were thenincubated in 1 L of 0.5 mol L−1 HCl at 50 ◦C for 2 h. The insolublefractions were washed once with 1 L of 0.25 mol L−1 HCl andneutralised with NaOH. The precipitates were washed twice with1.5 L of distilled water and freeze-dried.

Phosphorus concentration was determined as follows. Aliquotsof TF and SF (0.5 g dry matter) were decomposed in a 1 : 1 (v/v)mixture of 900 g L−1 nitric acid and 600 g L−1 perchloric acid(Wako). The solution was diluted to 50 mL with 20 g L−1 nitric acidin a measuring flask. The phosphorus concentration of each samplesolution was determined using a sequential plasma spectrometer(ICPS-7500, Shimadzu, Kyoto, Japan).

The total dietary fibre (991.43), insoluble fibre (991.43), water-soluble fibre (991.43), moisture (2001.12), crude protein (977.02)and ash contents of TF and SF were determined by AOAC methods(923.03).8

The particle size distributions of TF and SF were determined inair using sieves of 1700, 850, 600, 300 and 75 µm mesh (Marui &Co. Ltd, Osaka, Japan).

Physicochemical analysis of insoluble fibresThe water-holding capacity,7 swelling,9 oil-holding capacity10 andcation exchange capacity11 of TF and SF were determined by acentrifugation method (2000×g, 10 min), a bed volume technique,a centrifugation method (5000 × g, 30 min) and measurement ofcation in ashed solution of fibre respectively.

Animals and dietsTwelve 6-week-old male Wistar rats (body weight (mean ±standard error of mean) 257 ± 1.8 g, range 251–267 g) were

Table 1. Composition of study diets12

Component (g kg−1) Control Shiitake groupTossa jute

group

Dietary fibre – 50 50

Sucrose 550 500 500

Casein 200 200 200

DL-Methionine 3 3 3

Cornstarch (12.5% moisture) 150 150 150

Corn oil 50 50 50

AIN mineral mixture12 35 35 35

AIN vitamin mixture12 10 10 10

Choline bitartrate 2 2 2

Moisture 50 49 47

purchased from Japan SLC, Inc. (Shizuoka, Japan) and housedindividually in cages for 3 days prior to the start of the study. Theywere maintained at a room temperature of 24 ◦C and 60% relativehumidity in an animal room under a 12/12 h light/dark cycle. Therats were randomly divided into three groups of four animalseach using a random number table and dice. There were nodifferences in body weight among the three groups (P = 0.9). Therats were fed a semi-purified diet12 containing no fibre (control),50 g kg−1 TF or 50 g kg−1 SF ad libitum for 4 days (Table 1). It isknown that more than 99.9% of the gastrointestinal contents ofrats fed a commercial diet are displaced in 4 days.13 The rats weremaintained in accordance with the guidelines of Mie University forthe care of laboratory animals.

Viscosity of gastrointestinal tract contentsAll animals were slaughtered between 19 : 00 and 02 : 00, whichis the time of day when rodents eat and excrete actively,14

under diethyl ether anaesthesia by transection of the jugularvein. The gastric, small intestinal and caecal contents werecollected. The intestinal contents were maintained for 40 minat a room temperature of 3–10 ◦C at midnight in Decemberbefore measurement of their viscosity. It was confirmed thatdigesta viscosity did not change in 40 min. The coefficientof viscosity of whole digesta containing solid particles wasmeasured using an RVDV-I digital viscometer with a CPE-52 cone spindle (Brookfield Engineering, Middleborro, MA) at37 ◦C within 45 min of slaughter. The viscometer can measureparticles smaller than 1 mm. The digesta were kept on ice untilanalysis.

The free, bound and total water contents of digesta weredetermined using a centrifugation method15 to examine theirrelationship with digesta viscosity. The weights of digesta andtissue in the stomach, small intestine, caecum, proximal colon andmiddle plus distal colon were measured.

The aqueous fraction of digesta correlates with digestaviscosity.1,6 The correlations between free, bound and total watercontents of digesta and digesta viscosity were calculated toestimate the contribution of water content to digesta viscosity.The viscosity of digesta was calculated using the power equationof the viscosity and shear rate of digesta. The shear rate is thegradient of velocity in a flowing material.16 As the shear rate oforiginal digesta in the small intestinal lumen during peristalsisranges from approximately 24 to 49 s−1,4 the viscosities of thegastric, small intestinal and caecal contents in the control, TFand SF groups were calculated at a shear rate of 40 s−1. The

www.interscience.wiley.com/jsfa c© 2008 Society of Chemical Industry J Sci Food Agric 2009; 89: 245–250

24

7

Insoluble fibres and digesta viscosity www.soci.org

Table 2. Composition of dietary fibre fractions from shiitake andtossa jute8

Component (g kg−1) Shiitake fibres Tossa jute fibres

Yield 830 255

Moisture 35 34

Protein 90 104

Ash 38 84

Total dietary fibre 757 750

Soluble fibre 5 7

Insoluble fibre 752 743

Phosphate (mg kg−1) 20.5 42.5

Figure 1. Particle size distribution of insoluble fibres of tossa jute andshiitake.

Table 3. Physicochemical properties of dietary fibre fractions fromshiitake and tossa jutea,b

Shiitake fibres Tossa jute fibres

Component Mean SEM Mean SEM

Swelling (mL g−1) 14.7 0.1 33.3∗∗ 0.3

Water-holding capacity (mL g−1) 10.2 0.3 20.7∗∗ 0.4

Oil-holding capacity (mL g−1) 5.4 0.06 8.2∗∗ 0.09

Cation exchange capacity (meq g−1) 72 2.0 722.0∗∗ 6.5

a Fibre fractions were determined on a dry basis.b Values are given as mean and standard error of mean (SEM); n = 3.∗∗ Significantly different from shiitake fibres by ANOVA (P < 0.001).

correlation coefficients between digesta viscosity and free, boundand total water contents of digesta (n = 9, i.e. 3 dietary groups ×3 intestinal segments of digesta) were calculated after logarithmicconversion, which enabled the comparison of data of differentdimension (log xa = a log x).

Statistical analysisResults are expressed as mean and standard error of mean.Differences in body, tissue and digesta weights and intakeof rats among the control, TF and SF groups were analysedusing one-way analysis of variance (ANOVA) followed by Turkeymultiple comparison.17 Differences in digesta viscosity among thecontrol, TF and SF groups, the intestinal segments (gastric smallintestinal and caecal contents) and the shear rates (1–200 s−1)were analysed using three-way ANOVA followed by Turkeymultiple comparison.17 The relationships between the water-holding capacity of fibres (independent factor) and free, boundand total water contents (dependent factor) were analysed usinggeneral linear models.17 Differences were considered significantat P < 0.05. All statistical analyses were performed using JMPVersion 5 software (SAS Institute Japan, Tokyo, Japan).

RESULTS AND DISCUSSIONThe composition of TF was quite similar to that of SF (Table 2),i.e. both TF and SF had high insoluble fibre (743 and 752 g kg−1),

Figure 2. Effect of insoluble fibres of shiitake (SF) and tossa jute (TF) onviscosity of gastric, small intestinal and caecal contents in rats. Values areexpressed as mean with standard error for four rats. All linear regressionlines were statistically significant (P < 0.02). Coefficients of viscosity ofdigesta were in the order control < SF < TF in all intestinal segments,i.e. gastric, small intestinal and caecal contents (P < 0.05, Tukey multiplecomparison; Fig. 1). In the control group the viscosity of digesta was lowestin the stomach (P < 0.05, Tukey multiple comparison) and highest in thecaecum (P < 0.05, Tukey multiple comparison).

J Sci Food Agric 2009; 89: 245–250 c© 2008 Society of Chemical Industry www.interscience.wiley.com/jsfa

24

8

www.soci.org T Takahashi et al.

low soluble fibre (7 and 5 g kg−1), low moisture (34 and 35 gkg−1) and low protein (104 and 90 g kg−1) contents. Although theparticle size of insoluble fibres also affects digesta viscosity,1 theparticle size distribution did not appear to differ between the TFand SF groups (Fig. 1). A similar particle size distribution in digestashould show a similar effect on digesta viscosity.16 Thereforethe chemical composition and particle size distribution wereexcluded from our evaluation of the effects of physicochemicalproperties of insoluble fibres on digesta viscosity. Differencesbetween TF and SF were evident in phosphate content (Table 1),water-holding capacity, swelling, oil-holding capacity and cationexchange capacity (Table 3).

Insoluble fibres of tossa jute and shiitake consist mainly ofcellulose (β-1,4-glucan) and chitin (β-1,4-N-acetylglucosaminepolymer) respectively. The main difference between glucose andN-acetylglucosamine consist of the acetylated amino group at theC2 position of the sugar ring in the latter.

TF was a cellulose with phosphorylation. The effect of TF ondigesta viscosity was greater than that of cellulose in the rat (seebelow). Phosphorylation of TF should elevate digesta viscosity.

Body, tissue and digesta weights of ratsThe body weights of rats were not significantly different (P = 0.2)among the control (253 ± 2 g), TF (279 ± 21 g) and SF (266 ± 17 g)groups. The weight gains over 4 days were also not significantlydifferent (P = 0.9) among the control (2 ± 6 g), TF (24 ± 21 g) andSF (10 ± 18 g) groups. The daily food intakes were similar (P = 0.3)among the control (22±2 g), TF (23±2 g) and SF (25±2 g) groups.

There were no significant differences in tissue and digestaweights among groups, except for some specific differences in theweight of the caecal contents and the tissue weight of the Stomachand proximal colon (Table 4). The weights of the caecal contentsin both the TF (3.6 ± 1.3 g) and SF (3.4 ± 0.9 g) groups werehigher than that in the control group (1.4 ± 0.5 g; P < 0.02, Tukeymultiple comparison). The tissue weight of the proximal colon inthe TF group (0.4 + 0.0) was higher than that in the control group(0.3 + 0.0 g; P < 0.03, Tukey multiple comparison). Rubbing ofmucosa in the intestine by such insoluble fibres has been found to

stimulate hyperplasia of mucosa in the colon.2 Physical stimuli ofTF might be greater than those of SF.

Effects of insoluble fibres on digesta viscosityAlthough the three-way interaction among dietary groups,intestinal segments and shear rates on digesta viscosity was notsignificant (P = 1.0), the two-way interaction between dietarygroups and intestinal segments was significant (P < 0.001),suggesting that effects of fibres may vary among intestinalsegments. Therefore multiple comparison among groups wasperformed for each intestinal segment. The coefficients ofviscosity of digesta were in the order control < SF < TF in allintestinal segments, i.e. gastric, small intestinal and caecal contents(P < 0.05, Tukey multiple comparison; Fig. 2), indicating that theingestion of insoluble fibres from shitake and tossa jute increasedthe viscosity of gastric, small intestinal and caecal contents.Although crystalline cellulose also elevates digesta viscosity,2 theviscosities of the gastric, small intestinal and caecal contents in theTF group (Fig. 2) should be nine, three and one times (a shear rateof 40 s−1) those of rats fed a diet including crystalline cellulose2

respectively.In the control group the viscosity of digesta was lowest in the

stomach (P < 0.05, Tukey multiple comparison) and highest inthe caecum (P < 0.05, Tukey multiple comparison). In the TF andSF groups the viscosity of digesta was higher in the small intestinethan in the caecum (P < 0.05, Tukey multiple comparison).

Relationship between water content in digesta and water-holding capacityLines in the panels of Fig. 3 indicate the water content in digestadepending on the water-holding capacity. The total and freewater levels in the gastric and small intestinal contents decreasedas the water-holding capacity of insoluble fibres (see Table 3)increased (P < 0.003, linear effect in the general linear model;Fig. 3), while the bound water levels in the gastric and smallintestinal contents increased as the water-holding capacity offibres increased (P < 0.001, linear effect in the general linearmodel; Fig. 3). In the caecal contents the total water contentincreased slightly (P < 0.003, linear effect in the general linear

Table 4. Effect of dietary fibre fractions from shiitake and tossa jute on tissue and digesta weighta,b

Control Shiitake fibres Tossa jute fibres

Component Mean SEM Mean SEM Mean SEM

Contents

Stomach 8.1 3.0 15.5 6.2 11.4 7.3

Small intestine 1.0 0.1 1.7 1.0 2.2 1.3

Caecum 1.4A 0.5 3.4A 0.9 3.6B 1.3

Proximal colon 0.0 0.0 0.1 0.2 1.1 0.1

Middle plus distal colon 0.2 0.2 0.7 0.8 0.8 0.3

Tissue

Stomach 1.3A 0.1 1.4AB 0.1 1.5B 0.0

Small intestine 5.7 0.6 6.4 1.3 6.7 0.7

Caecum 0.9 0.1 1.2 0.2 1.1 0.1

Proximal colon 0.3A 0.0 0.4AB 0.1 0.4B 0.0

Middle plus distal colon 0.7 0.2 0.7 0.1 0.7 0.0

a Fibre fractions were determined on a dry basis.b Values are given as mean and standard error of mean (SEM); n = 4. Different letters in the same row indicate significant differences (P < 0.05).

www.interscience.wiley.com/jsfa c© 2008 Society of Chemical Industry J Sci Food Agric 2009; 89: 245–250

24

9

Insoluble fibres and digesta viscosity www.soci.org

Figure 3. Free, bound and total water contents plotted against water-holding capacity of insoluble fibres of control (none), shiitake and tossajute. Free, bound and total water contents were analysed by general linearmodels (Y = linear effect + quadratic effect of water-holding capacityof insoluble fibres). All linear regression lines represent significant lineareffects of the water-holding capacity of fibres (DF = 2, P < 0.003, DF oferror = 9). There was no quadratic effect of the water-holding capacity offibres in all relationships in the panels (DF = 1, P > 0.1, DF of error = 9).Symbols in the panels represent mean with standard error of mean; n = 4.Vertical bars represent standard error.

model) while the free water content decreased slightly as thewater-holding capacity of fibres increased (P < 0.001, linear effectof the water-holding capacity; Fig. 3). The bound water contentin the caecal contents was independent of the water-holdingcapacity of fibres (P = 0.1; Fig. 3). There was no quadratic effectof the water-holding capacity of fibres in all relationships in thepanels of Fig. 3 (P > 0.1).

Figure 4 shows that the free water content of digesta is stronglycorrelated with digesta viscosity (r = −0.89; n = 9; P < 0.01),suggesting that the free water content should be a direct factorfor elevating digesta viscosity as in a coal–water mixture.16

Water content in digesta and water-holding capacity ofinsoluble fibresThe free water content in digesta depended on the water-holdingcapacity of insoluble fibres in the gastric, small intestinal andcaecal contents represented as a linear function with negativeslope (Fig. 3), indicating that water-holding capacity should bea main factor for reducing the free water content in digesta asin previous studies.18,19 The free water content of fibres shoulddetermine the viscosity of a suspension of fibres.16 The water-holding capacity of insoluble fibres in experimental diets should

Figure 4. Viscosity at shear rate of 40 s−1 plotted against free, boundand total water contents of digesta. Viscosities were calculated using thepower equation of viscosity and shear rate of digesta in Fig. 1. Correlationcoefficients (r) between digesta viscosity and free, bound and total watercontents of digesta were calculated.

elevate digesta viscosity by decreasing the free water content indigesta.

Effects of swelling and cation exchange capacity of fibres onviscosityGenerally, both the water-holding capacity and swelling ofinsoluble fibres can affect their free water content18,19 andphysiological properties.20,21 Water-holding capacity is oftenrelated to swelling.18 The effect of water-holding capacity couldnot be distinguished from that of swelling in the present study.

The cation exchange capacity of fibres should create negativecharge on their surface.22 Negative charge on the surface of fibresshould affect digesta viscosity.16 The very high cation exchangecapacity of TF (Table 3) might also affect digesta viscosity. Themechanism of the effect of negative charge on the surface offibres on digesta viscosity is still unknown.16

Significance of insoluble fibres with high water-holdingcapacity and swellingOur previous study using a mathematical model suggests thatincreased digesta viscosity can diminish nutrient absorption,because self-diffusion of nutrients in digesta in the lumen, whichis correlated negatively with digesta viscosity,6 is a rate-limitingfactor in absorption.4 Indeed, the increase in digesta viscositydue to the addition of crystalline cellulose lowers the associatedblood glucose increment without the effects of gastric emptying,adsorption and dilution.5 Therefore the high digesta viscosity ofrats fed a diet including insoluble fibres with high water-holdingcapacity and/or swelling is likely to affect absorption.

The results of the present and previous studies1,23,24 suggestthat both soluble and insoluble fibres are responsible for digestaviscosity. Digesta viscosity should depend on water-holdingcapacity (see above), particle size1,16,19 and level of insolublefibres.1,16,19 This should be taken into account when addinginsoluble fibres, as well as soluble fibres, in our diets.

It has been shown that soluble fibres elevate the viscosity of thesupernatant of digesta.25The viscosity of whole digesta including

J Sci Food Agric 2009; 89: 245–250 c© 2008 Society of Chemical Industry www.interscience.wiley.com/jsfa

25

0

www.soci.org T Takahashi et al.

solid particles may also be increased by a diet with insoluble fibres.However, most studies employing soluble fibres did not determinethe viscosity of whole digesta including solid particles.3 Althoughthe effect of soluble fibres on blood glucose might be greater thanthat of insoluble fibres,26 it is difficult to compare the viscosities ofsoluble and insoluble fibres.

CONCLUSIONThe present study confirms the findings of previous studies1 – 4,27

and suggests that insoluble fibres can be responsible for increasingdigesta viscosity. The water-holding capacity and/or swelling ofinsoluble fibres can elevate digesta viscosity by decreasing thefree water content in digesta.

ACKNOWLEDGEMENTSThis study was partly supported by a Grant Aid for ScientificResearch (19.580154) and a Yazuya Research Grant 2008.

REFERENCES1 Takahashi T and Sakata T, Large particles increase viscosity and yield

stress of pig cecal contents without changing basic viscoelasticproperties. J Nutr 132:1026–1030 (2002).

2 Takahashi T, Yamanaka N, Sakata T and Ogawa N, Influence of solidparticles on the viscous properties of intestinal contents andintestinal tissue weight in rats. J Jpn Soc Nutr Food Sci 56:199–205(2003).

3 Takahashi T and Sakata T, Viscous properties of pig cecal contents andthe contribution of solid particles to viscosity. Nutrition 20:377–382(2004).

4 Takahashi T and Sakata T, Insoluble dietary fibers: the major modulatorfor the viscosity and flow behavior of digesta. Foods Food Ingred JJpn 210:944–953 (2005).

5 Takahashi T, Karita S, Ogawa N and Goto M, Crystalline cellulosedecreases blood glucose increment and stimulates waterabsorption associated with digesta viscosity in the rat. J Nutr135:2405–2410 (2005).

6 Antoon CB and Kirsch JF, Investigation of diffusion-limited ratesof chymotrypsin reactions by viscosity variation. Biochemistry21:1302–1307 (1982).

7 Yamazaki E, Murakami K and Kurita O, Easy preparation of dietary fiberwith the high water-holding capacity from food sources. Plant FoodsHum Nutr 60:17–23 (2005).

8 AOAC, Official Methods of Analysis (16th edn). Association of OfficialAnalytical Chemists, Arlington, VA (1995).

9 Ralet MC, Della Valle G and Thibault JF, Raw and extruded fibre frompea hulls. Part I. Composition and physico-chemical properties.Carbohydr Polym 20:17–23 (1993).

10 Adebowale KO and Lawal OS, Effect of annealing and heat moistureconditioning on the physicochemical characteristics of Bambarragroundnut (Volandzeia subterranean) starch. Nahrung 46:311–316(2002).

11 Chau CF and Huang YL, Comparison of the chemical andphysicochemical properties of different fibers prepared fromthe peel of Citrus sinensis L. cv Liucheng. J Agric Food Chem51:2615–2618 (2003).

12 Report of the American Institute of Nutrition Ad Hoc Committee onStandards for Nutritional Studies. J Nutr 107:1340–1348 (1977).

13 Sakaguchi E, Itoh H, Uchida S and Horigome T, Comparison of fibredigestion and digesta retention time between rabbits, guinea-pigs,rats and hamsters. Br J Nutr 58:149–158 (1987).

14 Takahashi T and Sakaguchi E, Behavior and nutritional importance ofcoprophagy in captive adult and young nutrias (Myocastor coypus).J Comp Physiol B 168:281–288 (1998).

15 Sakata T, Short-chain fatty acids and water in the hindgut contentsand feces of rats after hindgut bypass surgery. Scand J Gastroenterol22:961–968 (1987).

16 Borghesani AF, Non-Newtonian flow behavior of coal–fuel oilsuspensions, in Encyclopedia of Fluid Mechanics, Vol. 7, Rheologyand Non-Newtonian Flows, ed by Cheremisinoff NP. Gulf Publishing,Houston, TX, pp. 89–134 (1988).

17 Zar JH, Biostatistical Analysis (4th edn). Prentice-Hall, Englewood Cliffs,NJ (1999).

18 Takeda H and Kiriyama S, Correlation between the physical propertiesof dietary fibers and their protective activity against amaranthtoxicity in rats. J Nutr 109:388–396 (1979).

19 Darby R, Laminar flow and turbulent pipe flows of non-Newtonianfluids, in Encyclopedia of Fluid Mechanics, Vol. 7, Rheology andNon-Newtonian Flows, ed. by Cheremisinoff NP. Gulf Publishing,Houston, TX, pp. 19–54 (1988).

20 Takahashi R, Hirasawa Y and Nishinari K, Cellulose and its derivatives.Foods Food Ingred J Jpn 208:824–834 (2003).

21 Prakongpan T, Nitithamyaong A and Luangprtuksa P, Extraction andapplication of dietary fiber and cellulose from pineapple core. JFood Sci 67:1308–1313 (2002).

22 Ma C and Eggleton RA, Cation exchange capacity of kaoline. Clays ClayMiner 47:174–180 (1999).

23 Topping DL, Oakenfull D, Trimble RP and Illman RJ, A viscous fibre(methylcellulose) lowers blood glucose and plasma triacylglycerolsand increases liver glycogen independently of volatile fatty acidproduction in the rat. Br J Nutr 59:21–30 (1988).

24 Yamanaka N, Ogawa N, Takahashi T, Maki Y and Sakata T, Effects of theviscous exudate of Mekabu (sporophyll of Undaria pinnatifida) onglucose absorption in rats. Food Sci Technol Res 6:306–309 (2000).

25 Gallaher DD, Hassel CA and Lee KJ, Relationships between viscosity ofhydroxypropyl methylcellulose and plasma cholesterol in hamsters.J Nutr 123:1732–1738 (1993).

26 Takahashi T, Cellulose, in Handbook of Fiber Ingredients, ed. by Cho SS.CRC Press, Boca Raton, FL, pp. 263–282 (2008).

27 Takahashi T, Goto M and Sakata T, Viscoelastic properties of the smallintestinal and caecal contents of the chicken. Br J Nutr 91:867–872(2004).

www.interscience.wiley.com/jsfa c© 2008 Society of Chemical Industry J Sci Food Agric 2009; 89: 245–250