• Korean Journal of Food Science and Technology
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• v.47 no.6
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• pp.797-800
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• 2015

The effect of raw wheat flour on starch retrogradation retardation was investigated in a rice starch paste model. Specifically, in terms of amylase activity present in the wheat flour, the retardation effect was investigated depending on reaction temperature (40, 60, and $80^{\circ}C$), incubation time (0, 20, 40, and 60 min), and wheat flour addition levels (0-10%). An increase in wheat flour concentration resulted in a rapid decrease in the elastic modulus (G') as the incubation time increased. The G' changes of the rice starch pastes were furthermore fitted by the first order reaction for the reaction rate estimation on the temperature basis. The experimental reaction rate of the paste sample incubated with 10% wheat flour at $40^{\circ}C$ exhibited good agreement with the predicted value. This result implied that the first order reaction kinetics could be suitable to predict the changes in the G' as a function of incubation temperature and wheat flour concentration.

• Preventive Nutrition and Food Science
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• v.14 no.3
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• pp.233-239
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• 2009

The effects of guar gum (GG) and xanthan gum (XG) at different concentrations (0, 0.2, 0.4, and 0.6% w/w) on the rheological properties of Korean waxy rice starch (WRS) pastes were evaluated under both steady and dynamic shear conditions. The flow properties of WRS-gum mixtures were determined from the rheological parameters of the power law model. The addition of GG and XG to WRS resulted in an increase in the apparent viscosity ($\eta_{a,100}$) and consistency index (K) values obtained from power law model. The flow behavior index (n) values of the WRS-XG mixtures decreased with an increase in gum concentration while there was only a marginal difference between n values for the WRS-GG mixtures. Dynamic moduli (G', G", and $\eta^*$) values in the WRS-gum mixture systems also increased with an increase in gum concentration. WRS-XG mixtures had higher dynamic moduli and lower tan $\delta$ (ratio of G"/G') values than WRS-GG mixtures, indicating that the higher dynamic rheological properties of WRS-XG can be attributed to an increase in the viscoelasticity of the continuous phase in the starch-gum mixture systems, which was due to the higher viscoleastic properties of XG compared to GG. The dynamic ($\eta^*$) and steady shear ($\eta_a$) viscosities of the WRS-XG paste at a 0.2% gum concentration followed the Cox-Merz superposition rule.