Rheological properties of a polysaccharide isolated from Adansonia digitata leaves

The rheological properties of Adansonia digitata leaf polysaccharide were studied in dilute and semi-dilute solutions. The intrinsic viscosity of the polysaccharide obtained by Fedors equation and the combined Huggins and Kraemer extrapolations was ∼3.27 dL/g. The polysaccharide contained random coil macromolecules with mass average molecular mass of 4.01 × 106 g/mol. The polysaccharide in semi-dilute concentrations exhibited strong shear thinning property, and viscoelastic behaviour was observed with solutions within (3–5% (w/w)) consistent with the formation of entangled random coil macromolecules in solution. The polysaccharide solutions were sensitive to temperature and the minimum energy to initiate flow in 4.0% polysaccharide solution calculated from Arrhenius plot of zero shear viscosity as a function of temperature was 48.6 kJ/mol. The FTIR spectral studies of the polysaccharide confirmed the presence of uronic acid groups

Isolation and Rheological Characterization of Mucuna flagellipes Seed Gum

The gum from M. flagellipes seed endosperm has been isolated and characterised using capillary viscometry and steady shear and small deformation oscillatory rheometry. The endosperm was found to constitute 67.15% of the whole seed and yielded 32.6% of gum. The Huggins and Kraemer plots obtained by capillary viscometry gave an intrinsic viscosity of 7.9 dL/g and viscosity average molecular mass was calculated to be 2.1 x 106 using the Mark Houwink relationship. The zero shear viscosity was plotted against the coil overlap parameter, C[ç], and the slopes of the lines in the dilute and semi-dilute regions were found to be ~ 1.0 and 4.6 respectively. The curves were fitted to the Tuinier and Martin equations and showed only qualitative agreement. The shear flow viscosity profiles indicated that M. flagellipes gum did not exhibit significant shear thinning at polymer concentrations less than 0.5%, however, at higher concentrations, pronounced shear thinning was observed with the relaxation time (ô) increasing with increase in polymer concentration. The dynamic viscosity profiles showed that at all polymer concentrations examined, a Newtonian plateau was obtained at low frequencies indicating that the loss modulus was the dominant response. Plots of log ç versus log ﻵ and log ç* versus log ù were not superimposible and hence did not obey the Cox-Merz rule

Physicochemical properties of sorghum (sorghum bicolor l. Moench) starch as affected by drying temperature

 N. A. Aviara1, J. C. Igbeka2, L. M. Nwokocha3(1. Department of Agricultural and Environmental Resources Engineering, University of Maiduguri, Maiduguri, Nigeria;2. Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria;3. Department of Chemistry, University of Ibadan, Ibadan, Nigeria) Abstract: Starch was isolated from sorghum (white) grains and its proximate composition determined.  Scanning electron micrograph and x-ray diffraction pattern of the starch were obtained using scanning electron microscope and x-ray diffractometer, respectively.  The effect of drying temperature in a tray dryer on starch physicochemical and pasting properties was investigated.  The open air dried starch had a composition of 10.73% moisture, 0.30% ash, 1.06% protein and 1.07% fat.  Amylose content was 21.08% and it had an average granule size and pH of 18.59 μm and 5.45, respectively.  The starch exhibited the A-type crystalline diffraction pattern, which was not altered by drying in a tray dryer at the temperature range of 40 to 60℃.  Water binding capacity and swelling power of the open air dried starch were not significantly different from those of starch dried at 40℃ (p<0.05).  Water binding capacity increased from 79.63 to 88.5%, while swelling power, solubility and percentage syneresis decreased from 12.01 to 8.96 g/g, 7.08 to 2.85% and 14.00 to 10.80%, respectively as the drying temperature increased from 40 to 60oC.  Paste clarity was low (22.50%–26.20%) but increased with an increase in drying temperature up to 50℃ and decreased with a further increase in temperature.  Pasting properties of open air dried starch differed significantly from those of starch dried at different temperatures.  Peak viscosity decreased from 398.75 to 325.25 RVU as the drying temperature increased from 40 to 60℃.  Setback viscosity increased with an increase in drying temperature up to a point and decreased with a further increase in temperature.  Final and breakdown viscosities as well as pasting temperature and peak time had polynomial relationships of the third order with drying temperature.  Regression equations that could be used to adequately express the relationships existing between the physicochemical and pasting properties of sorghum starch and drying temperature were established.  These models could be used to select the drying temperature that would yield starch of desired physicochemical properties for a functional application.Keywords: sorghum starch, degree of crystallinity, physicochemical properties, pasting properties, drying temperature, tray dryer Citation: Aviara N. A, J. C. Igbeka, and L. M. Nwokocha.  Physicochemical properties of sorghum (sorghum bicolor l. Moench) starch as affected by drying temperature.  Agric Eng Int: CIGR Journal, 2010, 12(2): 85-94. &nbsp

Characterization of the polysaccharide from cola millenii seeds

We have isolated and characterized a water soluble polysaccharide from Cola millenii seeds. It was found to be composed of a total of 59% neutral sugars (mainly rhamnose, galactose and arabinose ~ 24, 13 and 8% respectively) and 41% uronic acids [mainly galacturonic acid]. The weight and number average molar mass values were found to be 4.7 x 106 g/mol and 3.5 x 106 g/mol, respectively. The polysaccharide exhibited polyelectrolyte properties with the intrinsic viscosity varying with salt concentration. The polysaccharide formed a highly viscous solution in water with apparent zero shear viscosities of 0.59 - 772 Pa.s at concentrations 0.3 - 2.5wt%. The solutions were shear thinning even at very low concentrations. The mechanical spectra showed gel-like characteristics at concentrations >2 wt%. The rheological behavior indicates the polysaccharide has potential for application as a thickener and suspending agent in food, pharmaceutical and cosmetic formulations

A comparative study of some properties of cassava (Manihot esculenta, Crantz) and cocoyam (Colocasia esculenta, Linn) starches

Some properties of cassava and cocoyam starches were studied and compared with a view to determining the functional applications in food systems for which they are suitable. The starches were compared in terms of their microscopic, thermal, physicochemical and rheological properties. Microscopy revealed smaller granule sizes of cocoyam starch compared with cassava. The amylose content was higher in cocoyam starch (33.3%) than in cassava starch (29.3%). Gelatinization in cassava starch occurred at a lower temperature range (60.11 o -72.67oC) compared with cocoyam (72.96o – 80.25oC) with the endothermic gelatinization enthalpy higher in cocoyam. The swelling power and solubility patterns indicated lower relaxation temperature, higher swelling and solubilization rates in cassava starch compared with cocoyam starch. The pasting characteristics of 8% (db, dry basis) starch slurry showed that cassava had higher peak viscosity but lower stability and setback ratios compared with cocoyam. This indicates that cocoyam starch paste is better in withstanding processing conditions and would present a superior thickening characteristic than cassava starch paste. The flow properties of both starch pastes showed non-Newtonian behaviour and could be best described by the Herschel-Bulkley model. The rate index and yield stress of cocoyam starch paste was higher than that of cassava. The storage modulus of cocoyam starch paste was higher than that of cassava indicating that cocoyam starch paste was more rigid than cassava starch paste. Cassava starch paste exhibited higher paste clarity and freeze-thaw stability than cocoyam starch paste. The properties of cassava and cocoyam starches dictate their food applications

Isolation and characterization of a novel polysaccharide from seeds of Peltophorum pterocarpum

Peltophorum pterocarpum seeds yielded ~20% water soluble polysaccharide. The polysaccharide is a galactomannan with mannose:galactose ratio of 4.4:1. The polysaccharide had an intrinsic viscosity of 3.14 dl/g and weight average molecular weight of 2.49 x 105 g/mol. The polysaccharide solutions were non-Newtonian at concentrations above 1%. A double logarithmic plot of the zero shear specific viscosity versus volume concentration gave a coil overlap concentration, c* of 2.6/[η], with slope c1.4 in the dilute regime and c4.3 in the concentrated regime. The experimental data were fitted to different viscosity models with the Martin model giving the best fit. The Cox-Merz empirical rule gave close superimposition of the data from steady shear viscosity η( ) and complex viscosity η*(ω)

Solution characteristics and thermorheology of Prosopis africana seed polysaccharide

Of about forty four species of the Prosopis family known, only Prosopis africana is indigenous to Africa. We have isolated the polysaccharide constituent of P.rosopisafricana seed and studied its solution properties. The polysaccharide had a weight-average molecular weight of 1.72 × 106 g/mol and intrinsic viscosity of 11.6 dL/g. The effect of concentration and temperature on the polysaccharide viscosity and microstructure were investigated under steady and dynamic shear. The polysaccharide showed typical shear thinning characteristics and the critical angular frequency at the G-crossover points (G′ = G″) was concentration and temperature dependent and shifted to lower frequencies at higher polysaccharide concentrations. The onset of polymer overlap occurred at a critical concentration, c* = 0.186 g/dL with slope of 1.4 below and 4.4 above the point of polymer overlap concentration. The rheological behavior was studied as a function of temperature and the activation energy for viscous flow of 2% solution of the polysaccharide was calculated to be 24.3 kJ/mol. The rheological properties were shown to be similar to guar gum and hence it has potential use as a thickener in foods

Hydrodynamic and rheological properties of Irvingia gabonensis gum

The polysaccharide component of Irvingia gabonensis endosperm was isolated and its hydrodynamic and rheological properties investigated. The polysaccharide is an arabinogalactan and contains small amounts of rhamnose, galacturonic acid, glucose and glucuronic acid. The polysaccharide displayed typical polyelectrolyte behaviour in solution. The intrinsic viscosity at infinite ionic strength, a measure of the hydrodynamic volume of the uncharged polysaccharide molecule, was obtained as 4.9 dl/g. The macromolecules have a semi flexible backbone with a Smidsrod stiffness parameter of 0.085. The polysaccharide exhibited non-Newtonian behaviour at all the concentrations (0.2% to 3.0% (w/v)) investigated. Cox-Merz plots showed that η( ) and η*(ω) were closely superimposable except at low shear rates and higher concentrations, where η* > η. The high Mw (1.56 x 106 g/mol) and its random coil conformation show Irvingia gabonensis polysaccharide has potential for application as thickener