The shear-thinning low, medium and high-viscosity fiber preparations (0.15–1.05% psyllium husk, 0.07–0.6% guar gum, 0.15–1.20% gum tragacanth, 0.1–0.8% gum karaya, 0.15–1.05% high-viscosity Carboxy Methyl Cellulose and 0.1–0.7% xanthan gum) showed that the consistency coefficient (k) was a function of concentration, the relationship being exponential (R 2, 0.87–0.96; P. IntroductionBased on solubility in water, dietary fiber is categorized as ‘insoluble’ and ‘soluble fiber’. Soluble fiber dissolves in water forming highly viscous fluid or gel.
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The high viscosity is responsible for the modified intestinal motility and delayed absorption of glucose in the intestines (Topping ). This property is beneficial for regulation of blood glucose and of appetite, and may also reduce the quantity of bile acids reabsorbed. The role of gums in satiety/satiation in formulated foods has been reviewed by Fiszman and Varela. This high viscosity is also believed to reduce the serum cholesterol and triglyceride levels, and increase the high density lipoprotein (HDL), or (good cholesterol) level, thus acting against hypercholesterolemia (Allen; Anderson et al. And Craig et al. Examples of soluble fibers include gums (plant extracts), pectins, mucilages, galactomannans, arabinogalactans, beta-glucans, non-digestible oligosaccharides and non-starchy water-soluble polysaccharides containing hemicelluloses.A major class of soluble fiber ingredients is hydrocolloids, frequently referred to as gums.
These compounds are polysaccharides that dissolve or disperse in water to give a thickening effect resulting in gel formation or increased viscosity (Cui et al. As food additives, these are used to stabilize emulsions, suspend particulates, control of crystallization, inhibition of syneresis, encapsulation, formation of films (Amiri et al.; Cui et al.; Phillips and Williams; Waldt, and Werbin ) and the reduced cooking loss in noodles (Kaur et al. They are classified as “generally recognized as safe” (GRAS) substances by the US Food and Drug Administration. Commercial soluble fiber preparationsSoluble fiber preparations like Xanthan gum, gum Acacia /gum Arabic, gum Tragacanth, gum Guar, gum Karaya were purchased from MP Biomedicals (Span), USA; Carboxy methyl cellulose (sodium salt) – High viscosity was purchased from Loba Chemie, Mumbai, India; Carboxy methyl cellulose (sodium salt) – Low viscosity was purchased from CDH, New Delhi, India; Psyllium ( Plantago ovata) husk: ‘Sat Isabgol’ was obtained from Sidhpur/Palani Group, Mumbai, India; Inulin (Raftiline ST) make ORAFTI (Belgium) was purchased from S.
Pharmachem, Mumbai, India and sugar was obtained from the local market. Preparation of fiber dispersionsInitially the concentrated solutions were prepared (levels are detailed in Table ) in order to find the suitable range of concentrations for each gum at which these gums/soluble dietary fibers would give an upper viscosity limit tolerable to drink/swallow. The upper concentration limit was worked out from the SVR and the suitable range of concentrations to study flow curve parameters for each soluble fiber were determined as can be studied with the Viscostar plus model L viscometer at the selected shear rates. Psyllium husk was used in ground form. Cyclotech 1093 sample mill ( Foss Techator, Sweden) fitted with a 0.5 mm sieve was used to grind the psyllium husk (predried at 105 °C/30 min) into a fine powder. Individual soluble fiber preparations were dispersed in distilled water at selected concentrations viz., guar gum, Arabic/acacia gum, xanthan gum, karaya gum, tragacanth gum, inulin, CMC (high viscosity), CMC (low viscosity) and ground psyllium husk were weighed into glass beakers, dry mixed with ground sugar (5.0%) and dispersed in agitated distilled water (except psyllium husk) on magnetic stirrer ‘Spinit’ using a small size (30 mm × 6 mm) magnetic bar at speed ‘7’.
After the complete transfer of weighed quantity of fiber into the water, the speed of the stirrer was increased to ‘10’ and the solution was stirred for another five minutes or till complete dissolution. Psyllium husk dispersion was blended using a wet hand blender make ‘Yamaha’ at speed I for 5 min. No.Name of soluble fiberConc.
Measurement of apparent viscosity and rheological propertiesThe samples were examined for the apparent viscosity using Viscostar Plus model L viscometer ( Fungilab, Spain) at 20 ± 1 °C. It is provided with the different attachments viz., LCP (small sample adapter), APM assembly of coaxial cylinders (spindles TL-5, TL-6, TL-7) and Heldal unit with T- shaped spindles (PA, PB, PC, and PD). In the present study the attachments used were LCP (small sample adapter) and APM assembly of coaxial cylinders (spindles TL-5, TL-6, TL-7). Specifically, for gum Arabic TL-5 was used, for inulin TL-5 and TL-6 were used, for CMC- low-viscosity TL-5 and TL-7 were used, for psyllium husk TL-5 and TL-6 were used, for guar gum LCP, TL-5 and TL-6 were used, for gum Tragacanth TL-5 and TL-7 were used, for gum Karaya TL-5 and TL-7 were used, for CMC-high viscosity TL-5, TL-6 and TL-7 were used and for gum Xanthan TL-5 and TL-7 were used. The apparent viscosity data obtained at different shear rates for each soluble fiber was used to develop instrumental flow behaviour (stress-shear rate flow curve) and regression equations were developed to know the relationship between k (Consistency coefficient), n (Flow-behaviour index), SVR (Sensory Viscosity Rating) and c (concentration). Sensory and rheological assessment of soluble fibersSoluble fibers mainly the gums are known to impart viscosity to the aqueous solutions.
Sensory viscosity rating (SVR) of soluble fibers dispersed in water at relatively high concentrations can be seen in Table, a higher value of SVR indicating lower viscosity. Psyllium husk (1.00–1.50%), xanthan gum (1.00–1.25%), gum karaya (1.00–1.25%), guar gum (1.50–2.00%), high-viscosity CMC (1.00–1.50%) and CMC-low viscosity (1.50–2.00%) yielded highly viscous solutions or non-flowable gels. On the other hand, low-viscosity fibers viz., gum acacia (10.0–20.0%) and inulin (15–20%) were reasonably fluid dispersions. Inulin (25%) in water tended to gel. The upper concentration limit was worked out from the SVR and the suitable range of concentrations to study flow-curve behaviour was found to be 3–21% for gum Arabic, 2.75–19.25% for inulin, 0.25–1.75% for CMC-low viscosity, 0.15–1.05% for psyllium husk (powdered), 0.07–0.6% for guar gum, 0.15–1.2% for gum tragacanth, 0.1–0.8% for gum karaya, 0.15–1.05% for CMC (high viscosity) and 0.1–0.7% for xanthan gum. In order to characterize the soluble gums with respect to their flow behaviour as a function of concentration, apparent viscosity was determined over the selected range of concentrations and flow-curve (shear stress-shear rate relationship) obtained.All the fibers in the low- and medium-viscosity category exhibited a ‘power-law’ relationship between the shear stress and shear rate i.e. With an increasing shear rate, the shear stress increased but at a decreasing rate (Figs., a and b).
This relationship could be expressed as follows. A Shear stress vs.
Shear rate relationship of different high-viscosity gums. B Shear stress vs.
Shear rate relationship of different high-viscosity gumsHere k is a measure of apparent viscosity and n is a measure of non-linearity of the shear stress-shear rate relationship. Higher the value of k, the greater is viscosity whereas the lower the value of n, the greater the non-linearity (abnormality). Polysaccharide solutions are known to show such a non-Newtonian or shear-thinning behaviour which is primarily interpreted as a progressive mechanical disentangling of molecule chains after initial entanglement, as shear rate increases (Launay et al. The shear thinning phenomena reflects decreasing viscosity with increasing shear rate.
Szczesniak and Farkas reported that the viscosity of pectin, CMC and sodium alginate declined with increasing shear rate, initially slowly and later rapidly, whereas that of guar gum, tragacanth, carrageenan, gum karaya and psyllium decreased rapidly in the beginning and slowly afterwards.Table shows the concentration-dependent flow-curve parameters of low- and medium- viscosity soluble fibers. The value of n was smaller for gum acacia (0.14–0.47) and inulin (0.18 at the highest concentration) as compared to that for low-viscosity CMC (0.34–0.60) thereby indicating that CMC showed a smaller non-newtonianness as compared to that of the other two fibers (Table ). At the lowest concentration, however, inulin solution (2.75%) exhibited essentially Newtonian flow behaviour. It can be further seen from the table that the consistency coefficient (k) was a function of concentration, the relationship being exponential (R 2, 0.87–0.96; P. No.Fiber prepara-tionConc.
Range (%) CPower law parameterRegression on CAppropriate Regression equationConsistency coefficient (k) mPa.s nFlow behaviour index (n)k vs. C or n vs.CLinearExponentialRR 2RR 21.GumAcacia3–21118.5–193.40.14–0.47k vs.
C0.96230.930.97090.94k = 111.28e 0.0251Cn vs. C0.83440.700.78960.62n = 0.1606Ln(C) - 0.00122.Inulin2.0.5–398.90.18–1.10k vs. C0.90120.810.93230.87k = 71.247e 0.0999Cn vs. C0.62780.390.60460.37-3.CMC, low viscosity0.25–1.75221.4–1288.00.34–0.60k vs. C0.97510.950.97810.96k = 200.27e 1.0903Cn vs.
The flow-curve characteristics of high-viscosity fiber preparations as presented in Table and Fig. A and b show that psyllium husk, guar gum, gum tragacanth, gum karaya, high-viscosity CMC and xanthan gum were all shear-thinning in nature as was expected from the earlier scientific findings (Thibault et al. The consistency coefficient (k) in all fibers and flow behaviour index (n) in all but gum karaya and CMC were directly related to concentration, the relationship largely being exponential (R 2, 0.61 to 0.98). The relatively smaller value of n for psyllium husk (0.13–0.44) and gum karaya (0.23–0.32) are indicative of greater non-Newtonianness of these solutions among the high-viscosity fibers. No.Fiber preparationConcentration (C) rangePower law parametersRegression on CAppropriate regression equationknLinearExponentialRR 2RR 21.Psyllium husk0.15–1.05250.5–1173.50.13–0.44k vs. C0.96230.930.99090.98k = 183.68e 1.7253Cn vs.
C0.96360.930.98650.97n = 0.356C + 0.032.Guar gum0.07–0.661.7–908.70.18–0.64k vs. C0.89960.810.78330.61k = 365.44Ln(C) + 1057.9n vs. C0.95560.910.96780.94n = 0.8765C + 0.06663.Gum tragacanth0.15–1.2130.0–1157.20.41–0.75k vs.
C0.93770.880.97830.96k = 107.74e 1.9583Cn vs. C0.86300.740.88380.78n = 0.272C + 0.31894.Gum karaya0.1–0.8312.3–3502.70.23–0.32k vs. C0.93100.870.98330.97k = 163.48e 3.8Cn vs. C0.17380.030.24350.06-5.CMC, high viscosity0.15–1.05252.9–1298.70.30–0.92k vs. C0.94850.900.86310.74k = 1355.9C – 198.81n vs.
C0.28480.080.41550.17-6.Xanthan gum0.1–0.7118.6–7493.80.18–0.67k vs. C0.97430.950.86140.74k = 13134C - 1037.8n vs. C−0.65890.430.66690.44n = 0.1358× -0.565C. Relationship between consistency coefficient (k) and sensory viscosity rating (SVR) of soluble-fiber dispersions in waterIt can be seen from Table that the lowest values of consistency coefficient (k) for gum Arabic (119–193 mPa.s n) and inulin (111 to 399 mPa.s n) corresponded with relatively higher values of SVR (the score being a direct measure of ‘fluidity’) (49 to 100), the negative correlation being highly significant (−0.98 and −0.94, respectively).
In case of other fibers, the relatively high values of k coincided with low values of SVR, the correlation coefficient (−0.79 to −0.99) being significant ( P. No.Fiber preparationConc. ConclusionThe low, medium and high-viscosity fiber preparations of gum Acacia, inulin, CMC-low viscosity, psyllium husk, guar gum, gum tragacanth, gum karaya, CMC high-viscosity and xanthan gum studied in the present study showed that the consistency coefficient (k) and the flow behaviour index (n) were dependent on concentration at a constant shear rate. The SVR could be predicted from k using the developed regression equations. Understanding the critical rheological parameters and their relationship with desired SVR, new product developers can develop healthy fiber-fortified products with acceptable consistency.
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