Cross-linked Waxy Corn Starch Research Articles

Viscoelastic Characterization of Corn Starch Paste: (I) The First Normal Stress Difference of a Cross-Linked Waxy Corn Starch Paste with Sucrose

Experimental viscoelastic data and the corresponding theoretical analysis of corn starch paste in the past 30 years indicate an evident deficiency of the viscoelastic characterization of the paste. The purposes of the study are to check the capability of a recent model on describing the viscoelasticity of the paste and to improve the viscoelastic analysis. The linear viscoelastic property; the steady shear viscosity and the first normal stress difference (N1) of a cross-linked waxy corn starch paste mixed with sucrose experimentally reported in 2003 were characterized with a structuralized viscoelastic constitutive equation in the present paper. The structuralized parameter f in the equation was obtained using the viscosities in the dynamic and steady shear experiment. Both a power law strain model and a linear strain model were proposed to describe the normal component in the strain matrix. Three kinds of viscoelastic properties of the paste can be described well with the structuralized equation. Both the power law and the linear strain model can yield reasonable calculations of N1. The maximum deviation of N1 calculated by two strain models is about 10%. The theoretical model adopted is available for describing the complex viscoelastic behaviors of corn starch paste usually appearing in the processing of corn starch.

Dialdehyde Oxidation of Cross-Linked Waxy Corn Starch: Optimization, Property and Characterization

The functionalization of waxy corn starch (WCS) was better realized by combing the cross-linking of epichlorohydrin with oxidation of sodium periodate. The results indicated that the cross-linking had a greater influence on the retrogradation than the oxidation, and the oxidation worsened the freeze–thaw stability of WCS. Both cross-linking and oxidation could ameliorate the alkali and acid resistance of WCS, and enhanced its heat stability. Cross-linking weakened the absorption peak of the –OH groups according to FTIR and had a small influence on the crystalline configuration of WCS belonging to a typical A-type structure, whereas the oxidation almost entirely damaged the particle structure. After the cross-linking, the tiny pits with a diameter of around 1 μm only appeared on sides of WCS granules, and proving that the cross-linking was very unevenly completed on some of WCS particles. The pasting curve of WCS was obviously different from those of its derivatives. The combination of oxidation and cross-linking could effectively decrease the setback of WCS.

Starch–cassia gum interactions: A microstructure – Rheology study

We present for the first time the interactions of starch and cassia gum – a novel galactomannan recently approved for use in food processing. Viscoelastic, pasting and microstructural characterization of various starches (waxy; high amylose; normal; cross-linked waxy corn starch; potato starch) containing different levels of the cassia gum was carried out. Significant changes were observed in the morphology of granule remnants formed during gelatinization in the starch pastes prepared with and without the addition of cassia gum. The freeze-dried starch–cassia gum pastes presented a shrunken and tight arrangement of the starch granule remnants, when studied by scanning electron microscopy. A significant reduction in the granule remnant size was also calculated using laser diffraction particle size analysis. The extent of interaction with cassia gum differed significantly among the various starch types. All the unmodified corn starches recorded an increase in peak viscosity at all levels of the cassia gum addition. An increase in the final viscosity of these starches was also observed by the addition of cassia gum, with high amylose and normal corn starch showing the maximum. Similarly, the extent of breakdown and setback viscosity also differed among the different starch types. Ranges of dynamic rheological measurements (temperature, time and frequency sweeps) were performed within the viscoelastic zones. Rheological parameters, such as storage modulus ( G′), loss modulus ( G″) and the gelatinization temperature ( T gel), of the corn starches during the heating cycle were observed to increase, when cassia gum was present at lower levels. The starch–gum systems also exhibited higher tan δ values during both the heating and the cooling cycles, indicating the dominance of the viscous modulus. The G′ and G″ of all the corn starch gels containing cassia gum showed higher values throughout the frequency sweep range. However, the increase in G′ and G″ of different starches was not always consistent with the increase in cassia gum levels. The changes in rheological behaviour during storage of the starch gels, aged on the plate of the rheometer and then studied through time sweeps at 5 °C and frequency sweeps at 25 °C, suggested that the starch gels containing cassia gum had less pronounced changes in the rheological parameters than had their control counterparts.

Structure of polysaccharide-starch composite gels by rheology and confocal laser scanning microscopy: Effect of the composition and of the preparation procedure

The aim of this study was to describe the structure of fruit preparations taken as models of polysaccharide-starch composite gels, according to the composition and the preparation procedure. For that purpose, model matrices have been prepared, the gelling agent being either pectin or carrageenan in combination with cross-linked waxy corn starch. The microstructure of these composite gels was studied by rheology and confocal laser scanning microscopy (CLSM) at different steps of the preparation procedure. The viscoelastic behaviour of these mixed systems clearly revealed the contribution of close-packed swollen starch granules in the dispersed phase and of the gelled network arising from the polysaccharide, located in the continuous phase. By CLSM, a heterogeneous microstructure with swollen starch granules unevenly distributed in the medium was shown. Pectin or carrageenan was mainly found in the continuous phase forming gelled fragments; part of the polysaccharide lay inside starch granules. These structural features are shown to be the direct consequence of the stirring applied during the cooling step of the preparation procedure while gelling of the polysaccharide took place. The resulting composite system was therefore more heterogeneous than expected.

Viscoelastic properties of cross-linked waxy cornstarch and κ-carrageenan mixtures under a wide range of potassium counter-ion concentrations

The small-deformation shear behavior at 25 °C of 1%–4%(mass fraction) cross-linked waxy corn starch (CWCS) and 0.5%(mass fraction) κC mixtures with and without KCl were studied. Dispersions were heated (1.5 °C/min) to 90 °C, held for 10 min, then cooled (1.5 °C/min) to 90 °C. When the volume fraction of CWCS is about 0.5 to 0.7, the rheological behavior is governed by the continuous phase, while above these values the disperse phase dominates the rheological behavior. When carrageenan is in a disordered state without KCl, the swollen granules are dispersed in a macromolecular solution. With KCl, the rigidity of the gels increases by effect of CWCS, carrageenan and salt concentrations. However, salt concentrations above 100 mmol/L lead to a marginal increase in rigidity. Results can be interpreted in terms of two types of systems: particles suspended in a macromolecular solution and composite gels of particles embedded in a network matrix when both κC and KCl were added.

Distribution of aroma in a starch–polysaccharide composite gel

The location of different aroma compounds in a gel containing sucrose, cross-linked waxy corn starch and carrageenan was investigated. Different systems were designed by varying the carrageenan and the sucrose contents and were flavoured with a mixture of aroma compounds. These systems are described as composite gels formed by a dispersed phase composed of swollen starch granules and a continuous phase containing the other polysaccharide. The separation of the two phases was done by centrifugation. The concentration in aroma compounds was measured in both phases and a partition coefficient was calculated for every compound in the different formulations. When the gel contained only starch, the distribution between the two phases for all aroma compounds was uniform. When carrageenan was present, the aroma compounds were found to be more concentrated in the continuous phase than in the dispersed phase. The addition of sucrose induced the opposite effect with a greater concentration of aroma compounds in the dispersed phase. The combination of these results with those of the gas/matrix partition is finally discussed to understand how the distribution of aroma compounds in a biphasic system influences aroma release in the headspace under equilibrium.

Dough properties and bread quality of flours supplemented with cross-linked cornstarches

Effects of cross-linked cornstarches (CLCSs) and vital gluten substituted for wheat flour (5–15%) on rheological properties and bread quality were tested. The substituted flours made stronger, more stable dough and bigger loaf volume than did the control. The substitution of low-swelling cross-linked waxy cornstarch (L-CWCS) made the dough softer and more extensible than that of low- and high-swelling cross-linked non-waxy cornstarches (L-CNCS and H-CNCS). The gelatinization and peak temperatures of the substituted flours were lower than those of the control, while the peak viscosity was higher. The firmness of breadcrumbs baked with L-CNCS (5% or 10%), H-CNCS (5% or 10%) or L-CWCS (5%, 10% or 15%) and vital gluten were softer than that from the control. In addition, the flour substituted with higher-swelling-degree CLCS (H-CNCS) had the stronger dough, bigger loaf volume and softer breadcrumbs than that with lower-swelling-degree CLCSs (L-CNCS or L-CWCS). From these results, an optimum amount of CLCS is expected to be used to improve dough and baking properties of wheat flour.

Dough properties and bread quality of flours supplemented with cross-linked cornstarches

Effects of cross-linked cornstarches (CLCSs) and vital gluten substituted for wheat flour (5–15%) on rheological properties and bread quality were tested. The substituted flours made stronger, more stable dough and bigger loaf volume than did the control. The substitution of low-swelling cross-linked waxy cornstarch (L-CWCS) made the dough softer and more extensible than that of low- and high-swelling cross-linked non-waxy cornstarches (L-CNCS and H-CNCS). The gelatinization and peak temperatures of the substituted flours were lower than those of the control, while the peak viscosity was higher. The firmness of breadcrumbs baked with L-CNCS (5% or 10%), H-CNCS (5% or 10%) or L-CWCS (5%, 10% or 15%) and vital gluten were softer than that from the control. In addition, the flour substituted with higher-swelling-degree CLCS (H-CNCS) had the stronger dough, bigger loaf volume and softer breadcrumbs than that with lower-swelling-degree CLCSs (L-CNCS or L-CWCS). From these results, an optimum amount of CLCS is expected to be used to improve dough and baking properties of wheat flour.

Effect of thermomechanical treatment on the rheological properties of crosslinked waxy corn starch

Cross-linked waxy maize starch (CWMS) are currently used as thickening or gelling agents in the food industries under high heating temperature and high shear conditions such as occurs, for example, in homogenizers. The rheological properties of CWMS dispersed in water have been studied in relation to its swelling behaviour. The main parameters that have been dealt with are starch concentration (2–4%), pasting temperature (90–130 °C) and shear conditions (∼10 5 s −1). The swelling behaviour was assessed by means of swelling experiments and particle size analysis. The rheological study was performed by means of steady shear measurements (viscometry) and in oscillatory shear (viscoelasticity). The rheological properties of CWMS suspensions were strongly dependent on the concentration regime of the suspension. A yield volume fraction of ∼0.4 was found to be critical. Beyond this value, starch dispersions exhibited the behaviour of suspensions of swollen particles, that means shear-thinning behaviour with a yield stress and measurable viscoelastic properties, typical of a gel-like system. All these properties strongly depended on the pasting temperature with an optimum around 124 °C for which the starch suspension was considered as “well-cooked”. Sensitivity of starch granules to shear forces was also strongly dependent on the pasting temperature. When starch granules were undercooked, their swelling properties, and hence their rheological properties were reinforced by additional high shearing. In contrast, when the starch granules were well-cooked or overcooked the rheological properties were depressed by shearing as a result of their high fragility. These overall results allowed evaluation of the role of the combined effect of heating temperature (above 100 °C) and shear conditions on the swelling behaviour and rheological properties of suspensions of CWMS in the formulation of starchy products.

Modified Waxy Wheat Starch Compared to Modified Waxy Corn Starch

Waxy wheat starch (WWS) and waxy corn starch (WCS) were cross-linked in an aqueous slurry at c. 37% starch solids with 0·013 to 0·050% phosphoryl chloride (starch basis) at pH 11·5 for 60 min in the presence of c. 2·1% sodium sulphate (starch basis). Increasing levels of phosphoryl chloride caused a steady decline in the final paste consistency of cross-linked WWS, but that of WCS proceeded through an optimum. Starch paste consistency was the resistance to stirring measured in a pasting instrument. WWS cross-linked at a low level gave a higher final paste consistency compared with cross-linked WCS. WWS and WCS were hydroxypropylated (HP) to low (c. 2·0%) and medium (c. 4·0%) levels by reaction with propylene oxide at pH 11·5 and 45 °C, and the HP starches were then cross-linked with 0·008 to 0·018% phosphoryl chloride. Again, cross-linked HP-WWS gave pasting curves with higher consistency at 6·25% starch solids compared with HP-WCS. WWS and its modified forms yielded pastes of lower clarity than those from WCS, but the pastes from HP/cross-linked WWS had better freeze-thaw stability. Cross-linking with phosphoryl chloride (0·025%) followed by acetylation with acetic anhydride (8·0%) yielded modified waxy wheat and waxy corn starches with similar paste consistencies, but a force-distance instrument indicated that the modified WCS was significantly stringier than the modified WWS.

Steady flow and viscoelastic behavior of crosslinked waxy corn starch-κ-carrageenan pastes and gels

The steady and small-deformation shear behaviors of 2–4wt.% cross-linked waxy corn starch (CWCS) and 0.5wt.% κ-carrageenan (κC) mixtures have been studied. In some cases κC gelation was induced by the addition of 20mM KCl and cooling to 25°C. Rheological behavior was interpreted considering swelling-solubility as well as laser diffraction particle size and size distribution data. CWCS was chosen because it lacks amylose and its granules can swell without disruption under appropriate thermal conditions; thus the condition of particles dispersed in a continuous phase can be best fulfilled. Dispersions were heated (1.5°C/min) to 96°C, held for 10min, then cooled (1.5°C/min) to 80°C. Steady tests were carried out at 60°C and oscillatory tests were carried out at 60 and 25°C. Only more concentrated dispersions displayed an anticlockwise up–down shear loop, which was enhanced by κC and KCl. Hysteresis disappeared with continuous shearing, and shear-thinning was observed with CWCS+κC being more viscous than CWCS+κC+KCl and CWCS. Oscillatory tests at 60°C showed that dispersions exhibited a predominantly solid-like behavior which was attenuated at lower starch concentrations and when κC and KCl were added. At 25°C, trends were similar but with slightly greater G′ and accentuated elastic character at higher starch concentrations. KCl-containing media formed gels whose rigidity depended on starch concentration. Solubility was low (<2%) and swelling increased from 25.3g/g up to 29.6g/g when κC was added, irrespective of starch concentration. Particle size data also showed higher swelling power in κC-containing media. Results could be interpreted in terms of two types of systems; particles suspended in a macromolecular solution and composite gels of particles embedded in a network matrix when both κC and KCl were added.

RHEOLOGICAL BEHAVIOUR OF THREE BIOPOLYMER/WATER SYSTEMS, WITH EMPHASIS ON YIELD STRESS AND VISCOELASTIC PROPERTIES

ABSTRACTFlow and viscoelastic properties of three thickened systems are presented: aqueous solutions of locust bean gum, of xanthan and a dispersion of a crosslinked waxy corn starch. Creep measurements allow investigations at very low shear rates. The existence of a yield stress is discussed. Flow was observed at low shear rates, but the starch paste exhibited pseudo‐yield stress behaviour. Dynamic measurements were performed and the relationships between flow curves and mechanical spectra are discussed.