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Flow properties of rye bran arabinoxylan dispersions
Food Hydrocolloids VoI.6 no.f pp.437-442. 1992
Flow properties of rye bran arabinoxylan dispersions A.Ebringerova and Z.Hromadkova Institute of Chemistry, Slovak Academy of Sciences, 842 38 Bratislava, CSFR Abstract. Two rye bran arabinoxylan fractions differing in sugar composition, structural features and solubility in water have been compared for the flow properties of their aqueous dispersions. The apparent viscosity of both fractions was strongly concentration- and temperature-dependent. The flow curves indicated pseudoplastic behaviour and a distinct thixotropy was evident for the watersoluble xylan.
Introduction
In view of the assumed correlation between physiological effects of bran and its polysaccharide components, the hemicelluloses of wheat (1,2), oats (3) and rice (4) have been studied in detail, The hemicelluloses of rye bran have received little attention, despite their high occurrence (5-8) in this important dietary fiber. Systematic investigations of the isolation and the molecular structure of selected arabinoxylan fractions from rye bran have been carried out in our laboratory (6,9,10). Two main arabinoxylan types, water-insoluble (WISX) and water-soluble (WSX), accounted together for >60% of cell wall polysaccharides. The rheological properties of these polysaccharides may be very important. They influence the processing of the whole kernel or bran-rich flours (5,11). Very positive effects on the baking properties of flours have also been observed by adding isolated xylans to low-quality flours (12,13). As dietary fibers they could influence many physiological activities (7,14). In spite of the low content of acidic sugars in bran (6) and of the low interactions of isolated rye bran xylan fractions with cations (15), a significant binding of minerals by bran in vivo (16) was observed. It is proposed that not only the chemical structure but also the physical properties of the xylans may help to clarify these effects as well as the biological function in plant cells. The object of this report is to investigate the flow properties of aqueous dispersions of both WSX and WISX rye bran fractions whose structure had been previously characterized (9,10). Materials and methods
Materials
Industrial rye bran (var. Breno, CSFR) ground to pass through a 0.2 mm mesh sieve was the starting material for the extraction of the arabinoxylan. Preparation of samples
Fractional extraction and isolation from rye bran has already been described in more detail (6). After the removal of fat, starch and pectin lignin were removed from the resulting material with a conventional acidic sodium chlorite treatment. 437
A.Ebringerova and Z.Hromadkova
A subsequent extraction with 1% NH 40H of the holocellulose obtained in this way produced the water-soluble arabinoxylan (WSX) which was isolated from the extract by precipitation with ethanol (1:2, v/v). The water-insoluble arabinoxylan (WISX) was obtained in the subsequent extraction step using 4.5% NaOH. The polysaccharide was precipitated from the extract by acidification to pH 5.5. Both precipitates were separated by centrifugation at 5000 g for 20 min, then suspended in distilled water and extensively dialyzed against distilled water. Freeze-drying of the non-dialyzable portion diluted to -1 mg em -3 yielded fine fluffy materials.
Analytical methods The procedures for chemical and physico-chemical analysis used for the analytical characterization of the arabinoxylans have been described in detail in previous papers (6,9,10). The monosaccharide composition was determined by gas-liquid chromatography of the alditol trifluoroacetate derivatives (17). Uronic acid content was alkalimetrically estimated by potenciometric titration (15). Nitrogen was determined by elemental analysis assayed on the PerkinElmer Elemental Analyzer Model 240. The number average molecular weight (Mn) was measured in DMSO on 'the Zweischicht-Membrane Knauer Osmometer using membrane type Schleicher-Schull RC 50. The optical rotation was measured at 21°C on a Perkin-Elmer Polarimeter Model 141 at concentration of 0.1 % in 2% NaOH (w/v). Relative viscosities were measured at 21°C in DMSO using a diluting Ubbelohde viscometer and the intrinsic viscosities [11] were obtained by extrapolation to infinite dilution.
Rheological properties Arabinoxylan dispersions were prepared on a w/w basis by preswelling WSX and WISX in distilled water for 1 h at ambient temperature and subsequent dispersion by thorough stirring for 1 h. Then the obtained dispersions were left to stand at IO'C for 24 h. In one experiment the dispersion was heated at 60°C for 20 min and then maintained at l O''C for 24 h at rest. All measurements were made at 20 ± 5°C on the Rheotest 2- Typ RV 2 (2-50 Hz; VEB MLW Prufgerate-Werk , Medingen, Germany) over the shear rate range of 1.51312 S-I. The shear rate (D) was changed stepwise and the samples were sheared until a constant shear stress (T) was reached. The apparent viscosities (11a, 11max) measured at shear rates 145 S-I and 1312 s-t, respectively, were calculated from values of the descending branch of the flow curves according to the equation 11a = TID. Analysis of the rheograms for general flow behaviour (non-Newtonian behaviour, thixotropy) was made by adjusting the curves mathematically to the Ostwald exponential function T = K. D", where K is the coefficient of consistency and n is the non-Newtonian flow index. Thixotropy was expressed by the area of the hysteresis loop (H) which was obtained as the difference of area integrals below both branches of the curves. Details are given in a previous paper (18). 438
Flow properties of rye bran fraction s
Results and discussion WSX a nd W ISX which were isola te d fro m the delignified ce ll-wall materials of de-lipid at ed , de-starched , and de-pectinated rye bran by a multi-step fractiona l extrac tion p rocedure (6) exhibit a high chemical puri ty with different pro porti ons of th e con stituting suga rs (Ta ble I) and with diffe re nt structura l pr operties. WISX (9) rep resented (1----,) 4)-f3 -D-xylan cha ins with a very low degree of substitution with single (1----,)3) -linked a-L-arabinofura nosy l side chai ns. Its water-so luble highly subs titute d structura l ana logue was isolated from rye flour (19-21). WSX (10) had only ~4 1 % of the D-xylan backb on e unsu bst ituted , -33% of the xylosyl un its wer e 2- or 3-subs tituted and the res t was disu bstituted. Residu es of arabinose, xylose and galacto se te rminated the side cha ins . a -L-Arabinof ura nosy l re sidues were attached to the xylan core as single units and onl y small proportions of them wer e 2-, 3-, or 5-linked . Althou gh WSX and WISX had similar number-aver age mol wts (M,,) (Table I) , the re was a significant differ enc e in the intrinsic viscosities of both fractions. This indicates that the polysacch arides adopt a differ ent mol ecular shape in DMSO solution due to their differ ent structural features. Am on g the various water-soluble ar abinoxylan fracti on s isolated from rye bran (Table I) , WSX had the highest [1"]] value , which was simi lar to that of other re porte d arabinoxy lans (80-310 crrr' g- l) (22-24) . H owever , it was conside rably lower th an the [1"]] of th e water-solub le whea t flour ara bino xylan (Ta ble I) which had a high asym me try of the chain (25) . From this aspe ct, the higher [1"]] of the low a nd irr egularly substitute d WISX in comparison to th at of WSX was unexpected as they exhibit more flexible chains. Th ey have th e tenden cy to form highly ordered macro structures through strong intermolecul ar hydrogen bonds (26) and to aggre gate in DMSO (27) . Het erogeneit y in composition and fine structure of th e compar ed xylans as well as differ en t solute-solvent int eraction s of the molecules in wa ter and DMSO could be the reason s for the observed viscosity beh aviour. Ta ble I. Che mical and physical characteristics of varous arabi noxylans Xylan
Rye bran (6) WSX WISX R ]-A/L R 2·B /L Wheat flour AX (25)
Sugar composition' (mo le %) Ara Xyl Glc
Ga l
43.5 11.9 42.5 35.5
55.6 85.3 50.0 36.2
0.4 0 6.0 5.1
33.0
67.0
0.5 1.7 I.5 5.1
VA " (%)
N
[ a l~
('Yo)
(degrees)
1.5 0
0 0 8.30 0.18
-115 -107 - 56 - 96
3.8
0.47
Mnc ,d
26 950 26650 13 500
169 265 22 152
65 0000 . 1 6151
Determined as aldito l trifluoro acet ates by g.l.c . o n OV-225. "Ca lculate d as 4-0- methyl-D-glucuronic acid .
439
A.Ebringerova and Z.Hromadkova
log '7Q
[mPe.a] 3,0
2,0
1,0
2
6
C [%]
Fig. I. Apparent viscosity (lJa) of aqueous solutions of WSX (1) and dispersions of WISX (2) as a function of concentration. Viscosity data were measured at constant shear rate D "" 145 S-I (at 20°C).
In order to suggest the importance of WSX and WISX in the processing of whole-grain rye meal, the flow properties of aqueous WSX solutions and WISX dispersions were characterized by current methods. The viscosities of the WSX solutions and WISX dispersions, respectively were strongly dependent upon concentration as seen in Figure 1. This feature was more pronounced in WISX. Similar behaviour was reported for starch solutions and suspensions within the same concentration range (28). Technical water-insoluble hemicelluloses of the xylan type produced suspensions with comparable viscosities at about ten times higher concentrations (29). Both the WSX solution and WISX dispersion exhibit a very low non-Newtonian index (n = 0.67 and 0.30 respectively). They are of the shear-thinning type (Figure 2) and show pseudoplastic behaviour. For WSX solutions a distinct thixotropy, expressed as the hysteresis loop area (H = 9160 Pas-I), was observed. WISX only swelled in water and formed dispersions with 440
Flow properties of rye bran fractions
1400
1000
500
50
100
150
T [Pal
Fig. 2. Flow curves of aqueous WSX soluti on and WISX dispersion: (1) WSX (3.9% w/w) , (2) WISX (5.0 % w/w) , (3) WISX (5.0% w/w) after heat pretreatment at 60°C) . All flow curves were recorded at 20°C.
an intrinsic structure which is disrupted at low shear rates. Measurable viscosities were attained only at high shear rates and therefore the descending part of the rheogram was used for the quantitative characterization of the flow properties. The ratio of the 'Yla:T]max measured at shear rates 145 and 1312 S-I , respectively, was used to express the ability of the dispersions to restore their intrinsic structure after maximal shearing. It was higher for the WISX dispersion (4.4) than for WSX solution (2.0) and decreased after short thermal pretreatment of WISX at 60°C (3.7) (Figure 2, curve 3). However, more subsequent investigations are planned to characterize the rheological properties of the rye bran xylans in detail. At least it can be assumed that not only WSX, but also WISX due to its higher abundance in bran, insolubility, highly ordered ultrastructure, and high concentration dependence of viscosity, can significantly contribute to the viscosity of the lumenal content at digestion and to many physiological effects of rye bran in the gastrointestinal tract (satiation effect , constipation , decrease of nutrient uptake, etc.). 441
A. Ebrillgero va and Z.Hromadkova
Refer ences 1. BrillouetJ .M .. Joselea u,J .P . , Uui lle.L l' . a nd Le-Le vre .D , (1982) J. Agric. Food Che m . , 30. 488-495. 2. Brillo uet ,J .M. and Jose lea u .L l' . (1987) Carbo hydr. Res. , \59 , 109- 126. 3 . Aspin aII.G .O . and Ca rpe nte r, R .C. ( 1984) Carbohydr. Res.. 4. 271-282. 4 . Sh ib uya .N , and lw asak i.T , (1985) Phytoch em istry , 24, 285- 289. 5. Meu ser ,F . , Suckov, P . and Ab d-E lgawad.A . (198 \) Get reide. MeM. Bro t. 35 . 172-176 . 6. H rom ad kova .Z. and Eb ringc rova .A . (1987) Die Nahru ng ; 3\ ,1 49-1 56. 7. Fenglcr .A il . a nd M arqu ar dt.R .R . ( 1988 ) Cereal Chem. , 65 , 289- 302 . 8. Holas.J .. Hampl.J. and Picrnan ova.B . (1972) Get reide . Meh l , Brat. 24.1 44-1 50 . 9 . H romad kova .Z.• Ebringer ova .A .. Petrakova .E. an d Schra rnl.J . ( 1987) Carbo hy dr. Res.. 163, 73-79. 10. Ebri nge rova .A .. H rom adk o va .Z .. Pet rak o va . E . a nd Hr icovin i.M. ( 1990) Carbohydr. Res. , \98 , 57-66. 11. McCleary,B . V., Gi bso n,T.S ., A llen , H . and Ga ms. T.e. ( 1986) Stae rke . 38 ,433- 437. 12. Lenz.J . and Wutzel .H . (1984) Rheol, Acta , 23. 570-572. 13. Mcuser .F ". Suckow .P . and A bd -Elgawad.A. (198 2) G etreide, Melli. BrOI, 36 . 1- 5. 14. Fur da .I . (1986) In Sti val a ,S.S. , Crescen zi. V. and Dca.lX' .M . (eds) , Industrial Polys accharides . Gordo n and Breach, Breach Scie nce Publishers . New York. pp . 195-202. 15. Kohn,R ., Hrornadkova.Z. an d Eb ringerova. A . (1986) Collect. Czec hos lovak . Chern, Commun., 5\ , 2250-2255. 16. Ward ,A.F. and Marquardt ,R.R . ( 1983) Poult. Sci .. 62,1054-1 062 . 17. Shapiro .J , (1969) Natur e, 222 , 792-793 . 18. Hr ornadk ova.Z. and Ebrin gerova .A , (199 1) Das Papier , 45 , 157- 162. 19. A spinall .GiO . and Cairn cross,I.M . ( 1960) J. Chern. Soc . , 3998- 4000 . 20 . Theande r .O . a nd A man ,P . ( 1979) Swed. J. Ag ric . Res. , 9 . 97-106 . 21. Ebringerova .A , , Vorwerg.W ,, Hrorn ad ko va .Z. and A tfoldi.J . (1990) Sth Bratis lava Sym posium on Sacc ha rides , Br at islava , A ugust 20-24 , Ab stract. p. 35. 22 . D ' Appoloni a ,B.L. and MacA rthu r-L. A . (1975) Cereal Chem .. 52, 230-239 . 23 . Fi nche r .G. B. and Sto ne .B.A . (1974) A ilS/' J. Bioi. Sci.. 24. 117- 132. 24. MedCalf.D .G .. D ' Appolon ia . B.L. and Gil les .K iA . ( 1968) Cereal Chern.. 45 . 539-549. 25. A ndrewa rt ha ,K .A .. P hillips .D.R . and Sto ne ,B.A . ( 1979) Carbohydr. Res. . 77 . 191- 204. 26 . Ebr ingerova .A . , Kacur akova .M. and Pr uzinec .J . (1990) J. Radioanal. Nuc l. Che m . Letters . \44 . 297-305 . 27 . Eb rlngerova .A ., Hrom adk ova .Z .. Burch ard ,W., Vo rwer g.W . and Ber th .G . ( 1991) 8th Bratislava Int ern ation al Conference all Polym ers , Star a Lesna. CSF R . Ju ne 10-14 ( 1991). 28 . Ste e ne ken, P.A. M . (1989) Carbohydr . Polym . . 11. 23-42. 29 . Le nz,J ., Sch urz ,J . and Uj he ly.W . ( 1986) Rh eol . Acta , 25, 418- 425 .
442
Flow properties of rye bran arabinoxylan dispersions A.Ebringerova and Z.Hromadkova Institute of Chemistry, Slovak Academy of Sciences, 842 38 Bratislava, CSFR Abstract. Two rye bran arabinoxylan fractions differing in sugar composition, structural features and solubility in water have been compared for the flow properties of their aqueous dispersions. The apparent viscosity of both fractions was strongly concentration- and temperature-dependent. The flow curves indicated pseudoplastic behaviour and a distinct thixotropy was evident for the watersoluble xylan.
Introduction
In view of the assumed correlation between physiological effects of bran and its polysaccharide components, the hemicelluloses of wheat (1,2), oats (3) and rice (4) have been studied in detail, The hemicelluloses of rye bran have received little attention, despite their high occurrence (5-8) in this important dietary fiber. Systematic investigations of the isolation and the molecular structure of selected arabinoxylan fractions from rye bran have been carried out in our laboratory (6,9,10). Two main arabinoxylan types, water-insoluble (WISX) and water-soluble (WSX), accounted together for >60% of cell wall polysaccharides. The rheological properties of these polysaccharides may be very important. They influence the processing of the whole kernel or bran-rich flours (5,11). Very positive effects on the baking properties of flours have also been observed by adding isolated xylans to low-quality flours (12,13). As dietary fibers they could influence many physiological activities (7,14). In spite of the low content of acidic sugars in bran (6) and of the low interactions of isolated rye bran xylan fractions with cations (15), a significant binding of minerals by bran in vivo (16) was observed. It is proposed that not only the chemical structure but also the physical properties of the xylans may help to clarify these effects as well as the biological function in plant cells. The object of this report is to investigate the flow properties of aqueous dispersions of both WSX and WISX rye bran fractions whose structure had been previously characterized (9,10). Materials and methods
Materials
Industrial rye bran (var. Breno, CSFR) ground to pass through a 0.2 mm mesh sieve was the starting material for the extraction of the arabinoxylan. Preparation of samples
Fractional extraction and isolation from rye bran has already been described in more detail (6). After the removal of fat, starch and pectin lignin were removed from the resulting material with a conventional acidic sodium chlorite treatment. 437
A.Ebringerova and Z.Hromadkova
A subsequent extraction with 1% NH 40H of the holocellulose obtained in this way produced the water-soluble arabinoxylan (WSX) which was isolated from the extract by precipitation with ethanol (1:2, v/v). The water-insoluble arabinoxylan (WISX) was obtained in the subsequent extraction step using 4.5% NaOH. The polysaccharide was precipitated from the extract by acidification to pH 5.5. Both precipitates were separated by centrifugation at 5000 g for 20 min, then suspended in distilled water and extensively dialyzed against distilled water. Freeze-drying of the non-dialyzable portion diluted to -1 mg em -3 yielded fine fluffy materials.
Analytical methods The procedures for chemical and physico-chemical analysis used for the analytical characterization of the arabinoxylans have been described in detail in previous papers (6,9,10). The monosaccharide composition was determined by gas-liquid chromatography of the alditol trifluoroacetate derivatives (17). Uronic acid content was alkalimetrically estimated by potenciometric titration (15). Nitrogen was determined by elemental analysis assayed on the PerkinElmer Elemental Analyzer Model 240. The number average molecular weight (Mn) was measured in DMSO on 'the Zweischicht-Membrane Knauer Osmometer using membrane type Schleicher-Schull RC 50. The optical rotation was measured at 21°C on a Perkin-Elmer Polarimeter Model 141 at concentration of 0.1 % in 2% NaOH (w/v). Relative viscosities were measured at 21°C in DMSO using a diluting Ubbelohde viscometer and the intrinsic viscosities [11] were obtained by extrapolation to infinite dilution.
Rheological properties Arabinoxylan dispersions were prepared on a w/w basis by preswelling WSX and WISX in distilled water for 1 h at ambient temperature and subsequent dispersion by thorough stirring for 1 h. Then the obtained dispersions were left to stand at IO'C for 24 h. In one experiment the dispersion was heated at 60°C for 20 min and then maintained at l O''C for 24 h at rest. All measurements were made at 20 ± 5°C on the Rheotest 2- Typ RV 2 (2-50 Hz; VEB MLW Prufgerate-Werk , Medingen, Germany) over the shear rate range of 1.51312 S-I. The shear rate (D) was changed stepwise and the samples were sheared until a constant shear stress (T) was reached. The apparent viscosities (11a, 11max) measured at shear rates 145 S-I and 1312 s-t, respectively, were calculated from values of the descending branch of the flow curves according to the equation 11a = TID. Analysis of the rheograms for general flow behaviour (non-Newtonian behaviour, thixotropy) was made by adjusting the curves mathematically to the Ostwald exponential function T = K. D", where K is the coefficient of consistency and n is the non-Newtonian flow index. Thixotropy was expressed by the area of the hysteresis loop (H) which was obtained as the difference of area integrals below both branches of the curves. Details are given in a previous paper (18). 438
Flow properties of rye bran fraction s
Results and discussion WSX a nd W ISX which were isola te d fro m the delignified ce ll-wall materials of de-lipid at ed , de-starched , and de-pectinated rye bran by a multi-step fractiona l extrac tion p rocedure (6) exhibit a high chemical puri ty with different pro porti ons of th e con stituting suga rs (Ta ble I) and with diffe re nt structura l pr operties. WISX (9) rep resented (1----,) 4)-f3 -D-xylan cha ins with a very low degree of substitution with single (1----,)3) -linked a-L-arabinofura nosy l side chai ns. Its water-so luble highly subs titute d structura l ana logue was isolated from rye flour (19-21). WSX (10) had only ~4 1 % of the D-xylan backb on e unsu bst ituted , -33% of the xylosyl un its wer e 2- or 3-subs tituted and the res t was disu bstituted. Residu es of arabinose, xylose and galacto se te rminated the side cha ins . a -L-Arabinof ura nosy l re sidues were attached to the xylan core as single units and onl y small proportions of them wer e 2-, 3-, or 5-linked . Althou gh WSX and WISX had similar number-aver age mol wts (M,,) (Table I) , the re was a significant differ enc e in the intrinsic viscosities of both fractions. This indicates that the polysacch arides adopt a differ ent mol ecular shape in DMSO solution due to their differ ent structural features. Am on g the various water-soluble ar abinoxylan fracti on s isolated from rye bran (Table I) , WSX had the highest [1"]] value , which was simi lar to that of other re porte d arabinoxy lans (80-310 crrr' g- l) (22-24) . H owever , it was conside rably lower th an the [1"]] of th e water-solub le whea t flour ara bino xylan (Ta ble I) which had a high asym me try of the chain (25) . From this aspe ct, the higher [1"]] of the low a nd irr egularly substitute d WISX in comparison to th at of WSX was unexpected as they exhibit more flexible chains. Th ey have th e tenden cy to form highly ordered macro structures through strong intermolecul ar hydrogen bonds (26) and to aggre gate in DMSO (27) . Het erogeneit y in composition and fine structure of th e compar ed xylans as well as differ en t solute-solvent int eraction s of the molecules in wa ter and DMSO could be the reason s for the observed viscosity beh aviour. Ta ble I. Che mical and physical characteristics of varous arabi noxylans Xylan
Rye bran (6) WSX WISX R ]-A/L R 2·B /L Wheat flour AX (25)
Sugar composition' (mo le %) Ara Xyl Glc
Ga l
43.5 11.9 42.5 35.5
55.6 85.3 50.0 36.2
0.4 0 6.0 5.1
33.0
67.0
0.5 1.7 I.5 5.1
VA " (%)
N
[ a l~
('Yo)
(degrees)
1.5 0
0 0 8.30 0.18
-115 -107 - 56 - 96
3.8
0.47
Mnc ,d
26 950 26650 13 500
169 265 22 152
65 0000 . 1 6151
Determined as aldito l trifluoro acet ates by g.l.c . o n OV-225. "Ca lculate d as 4-0- methyl-D-glucuronic acid .
439
A.Ebringerova and Z.Hromadkova
log '7Q
[mPe.a] 3,0
2,0
1,0
2
6
C [%]
Fig. I. Apparent viscosity (lJa) of aqueous solutions of WSX (1) and dispersions of WISX (2) as a function of concentration. Viscosity data were measured at constant shear rate D "" 145 S-I (at 20°C).
In order to suggest the importance of WSX and WISX in the processing of whole-grain rye meal, the flow properties of aqueous WSX solutions and WISX dispersions were characterized by current methods. The viscosities of the WSX solutions and WISX dispersions, respectively were strongly dependent upon concentration as seen in Figure 1. This feature was more pronounced in WISX. Similar behaviour was reported for starch solutions and suspensions within the same concentration range (28). Technical water-insoluble hemicelluloses of the xylan type produced suspensions with comparable viscosities at about ten times higher concentrations (29). Both the WSX solution and WISX dispersion exhibit a very low non-Newtonian index (n = 0.67 and 0.30 respectively). They are of the shear-thinning type (Figure 2) and show pseudoplastic behaviour. For WSX solutions a distinct thixotropy, expressed as the hysteresis loop area (H = 9160 Pas-I), was observed. WISX only swelled in water and formed dispersions with 440
Flow properties of rye bran fractions
1400
1000
500
50
100
150
T [Pal
Fig. 2. Flow curves of aqueous WSX soluti on and WISX dispersion: (1) WSX (3.9% w/w) , (2) WISX (5.0 % w/w) , (3) WISX (5.0% w/w) after heat pretreatment at 60°C) . All flow curves were recorded at 20°C.
an intrinsic structure which is disrupted at low shear rates. Measurable viscosities were attained only at high shear rates and therefore the descending part of the rheogram was used for the quantitative characterization of the flow properties. The ratio of the 'Yla:T]max measured at shear rates 145 and 1312 S-I , respectively, was used to express the ability of the dispersions to restore their intrinsic structure after maximal shearing. It was higher for the WISX dispersion (4.4) than for WSX solution (2.0) and decreased after short thermal pretreatment of WISX at 60°C (3.7) (Figure 2, curve 3). However, more subsequent investigations are planned to characterize the rheological properties of the rye bran xylans in detail. At least it can be assumed that not only WSX, but also WISX due to its higher abundance in bran, insolubility, highly ordered ultrastructure, and high concentration dependence of viscosity, can significantly contribute to the viscosity of the lumenal content at digestion and to many physiological effects of rye bran in the gastrointestinal tract (satiation effect , constipation , decrease of nutrient uptake, etc.). 441
A. Ebrillgero va and Z.Hromadkova
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