Cross-linked Waxy Maize Starch Research Articles

Rheology and Relationship among Rheological Parameters of Cross‐Linked Waxy Maize Starch Dispersions Heated in Fructose Solutions

ABSTRACT: Dispersions of 5% cross‐linked waxy maize starch heated in Newtonian aqueous fructose solutions, 0 to 600 g per kg, exhibited either thixotropic or antithixotropic flow behavior, and viscoelastic behavior. The mean starch granule dia in the dispersions changed slightly with fructose content. Values of G' of the dispersions were higher than those of G', reflecting gel‐like behavior of the dispersions. Values of the first normal stress coefficient predicted from dynamic rheological and apparent viscosity data based on the Goddard‐Miller model were in reasonable agreement with experimental values.

Influence of sucrose on the rheology and granule size of cross-linked waxy maize starch dispersions heated at two temperatures

Cross-linked waxy maize (CWM) starch dispersions (STDs) of concentration 50 g kg −1 were heated in sucrose solutions containing 0–600 g kg −1 (g sucrose/kg dispersion) at 85 °C at low shear and in intermittently agitated cans at 110 °C. The STDs heated in 0–300 g kg −1 sucrose exhibited antithixotropic behavior, while those heated in 400–600 g kg −1 sucrose exhibited thixotropic behavior. The mean starch granule diameter of the starch dispersions did not show strong dependence on sucrose concentration. The dispersions, especially those with high sucrose concentrations and heated at 110 °C, exhibited G′ versus frequency ( ω) profiles of gels. The STDs exhibited first normal stress differences that increased in magnitude with the concentration of sucrose. Values of the first normal stress coefficient of canned dispersions calculated from dynamic rheological data plotted against ω and experimental values plotted against shear rate of some of the STDs overlapped.

Effects of Modification Sequence on Structures and Properties of Hydroxypropylated and Crosslinked Waxy Maize Starch

The effects of modification sequence on chemical structures and physicochemical properties of hydroxypropylated (HP) and crosslinked (XL) waxy maize starch were investigated. The physicochemical properties, including pasting, gelling, and thermal properties, were studied. The chemical structures of dual-modified starches and their beta-limit dextrins were characterized with high-performance liquid chromatography. The HP-XL starch had higher Brabender viscosity than did the XL-HP starch at both pH 7 and 3; however, both showed similar gelling properties. Significantly higher onset and peak gelatinization temperatures, gelatinization enthalpy, and lower retrogradation were observed for the HP-XL starch. The HP-XL starch also exhibited significantly higher beta-amylolysis limit and higher content of low molecular weight saccharides in its isoamylase-debranched starch, suggesting its structure was more accessible to enzymatic attack than the XL-HP starch. Structural analyses revealed different distribution patterns of modifying groups between the two modified starches. The results indicate that the modification sequence altered the susceptibility to enzymes, changed the locations of substitution, and modified the physicochemical properties of the HP and XL waxy maize starches.

Rheological behavior of cross-linked waxy maize starch dispersions during and after heating

A model was developed to describe the complex viscosity versus temperature (η ∗–T) data on 5% (w/w) cross-linked waxy maize (CWM) starch dispersions (STDs) obtained over the frequency range ( ω) 1.26–31.38 rad s −1 and temperature range 55–95°C. The 5% CWM starch dispersions had an onset gelatinization temperature at 60°C with a peak complex viscosity (η peak ∗) of 6.9 Pa s at 64°C. The lowest post-gelatinization complex viscosity ( η ∗) was about 0.85η peak ∗ at 80°C. The complex viscosity was related to the apparent viscosity using a Modified Cox–Merz rule. Flow tests on gelatinized 5% CWM STDs showed that the sample exhibited a combined time-dependent shear-thickening (antithixotropic) and time-dependent shear-thinning (thixotropic) behavior. The antithixotropic behavior, that appears to have resulted from a shear-induced structure formation, predominated when the level of shear stress imposed on the sample was less than 120–150 Pa.

Application of polymer blending laws to composite gels of agarose and crosslinked waxy maize starch

Composites comprising swollen granules of highly crosslinked waxy maize starch in an agarose gel matrix have been prepared in two ways: (i) by gelatinising the starch in agarose solution at 80 °C and then cooling to form the gel network, or (ii) by cooling to gel the agarose and then heating to gelatinise the starch. In the first procedure, phase volumes were derived by using centrifugation to obtain a sample of the agarose phase prior to gelation, and determining the increase in polymer concentration due to swelling of the starch granules. The storage modulus ( G') of the agarose phase was obtained by gelling the supernatant from centrifugation, under identical time-temperature conditions to those used for the unseparated composite, and the value of G' for the swollen granules was derived by the ‘model independent’ method of varying polymer concentration to determine compositions at which both phases (and hence the overall composite) have the same modulus. Measured values of G' for the composite gels agreed, to within experimental error, with values calculated by application of the Takayanagi blending laws, with no adjustable parameters, using the isostress model for systems in which the continuous matrix was weaker than the dispersed particles and the isostrain model for the converse situation (weak filler in strong matrix). For composites formed by the second procedure, the increase in modulus of the continuous phase due to swelling of starch granules within the agarose gel network was calculated by classic swelling/deswelling theory, and the resulting values of G' obtained by application of the polymer blending laws were again in close agreement with those observed experimentally.

Rheological properties of highly cross-linked waxy maize starch in aqueous suspensions of skim milk components. Effects of the concentration of starch and skim milk components

The storage modulus of various concentrations of highly cross-linked waxy maize starch was measured in water, a salt solution, a salt solution with lactose, whey, and skim milk. The influence of the skim milk components was deduced from the differences in moduli between these systems. Salts appeared to have no direct influence on the modulus of the starch. Lactose increased the storage modulus, probably due to an increase in the particle rigidity of the swollen starch granules. The whey proteins had only a small effect on the modulus of the starch. However, the concentration of these proteins was very low. Casein micelles increased the modulus of the starch because the swollen starch granules are not accessible to the casein. A model based on the mutual exclusion of swollen starch granules and milk proteins was applied to predict the storage modulus of starch-milk systems as a weighed sum of the moduli of the starch and protein phases. Weight factors were derived from the hydration capacity of starch granules and casein micelles. Although the behaviour of aqueous starch-skim milk systems fell within the boundaries imposed by the model, the predictive power of this model was rather poor.

Rheological properties of starch solutions under aseptic processing temperatures

Rheological properties of cross-linked waxy maize starch in the concentration range of 3–6% w w were evaluated using a computer controlled rotational viscometer equipped with a high temperature/high pressure attachment and a magnetic coupling. The influence of temperature on the rheological parameters was evaluated in the temperature range 60–140 °C. The flow curves essentially followed the power law model and both the consistency coefficient and flow behaviour index were sensitive to changes in temperature and concentration. Temperature dependency followed the Turian model.

Rheological properties of highly cross-linked waxy maize starch in skim milk

Rheological properties of highly cross-linked waxy maize starch in skim milk

LITERATURE ABSTRACTS

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Rheological Characterization of Crosslinked Waxy Maize Starch Solutions under Low Acid Aseptic Processing Conditions using Tube Viscometry Techniques

ABSTRACTA rheological characterization of 1.82 and 2.72% (g dry starch/100g water) waxy maize starch solutions was performed at 121.1, 132.2, and 143.3°C using tube viscometry techniques. Dilatancy was observed in 22 out of 23 experiments and the flow behavior index increased with concentration and decreased with temperature. Rheological behavior was explained in terms of the rigidity and volume fraction of the swollen granules combined with small shear stresses in the fluid due to the high temperatures and low shear rates. Parameter correlation analysis showed a near correlation between rheological parameters with the flow behavior index being the dominant parameter. The effect of dilatancy on residence time and heat transfer in the aseptic processing of particulate and nonparticulate foods is discussed.

A Study of Starch‐Lipid Interactions for Some Native and Modified Maize Starches

AbstractStarch‐lipid interactions of five maize starches varying in amylose content and chemical modification were investigated by differential scanning calorimetry (DSC). The high‐amylose maize starch gave the greatest endotherm due to the amylose‐lipid complex in presence of cetyltrimethylammonium bromide (CTAB). This endotherm was decreased in an acetylated high‐amylose maize starch, and the waxy varieties did not give rise to such an endotherm. However, when the gelatinization enthalpies were compared it was found that these values decreased also for waxy varieties in the presence of CTAB. Dynamic rheological measurements showed that CTAB increased the storage modulus (G′) for all the starches investigated (normal maize starch, acetylated high‐amylose maize starch and crosslinked waxy maize starch), whereas saturated monoglycerides increased G′ for normal maize starch, decreased G′ for the crosslinked waxy maize starch and left acetylated high‐amylose maize starch unaffected. Lecithin and soybean oil either decreased G′ or had no effect.