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ABSTRACT
The aim of this study was to characterize rheological properties of shear-thinning polysaccharides (guar gum, κ-carrageenan, xanthan gum), which are widely used as food hydrocolloids in food processing. Viscometric analysis of the polysaccharides solutions both in distilled water and in 0.07M KCl at the temperature range of 20 to 45 °C confirmed strong concentration dependency of the solutions viscosities as reflected in observed significant changes of the flow parameters, calculated by the Ostwald-de Waele and Herschel-Bulkley rheological models. The consistency coefficient (k) of the solutions increased with concentration, whereas the flow behaviour index (n) decreased in all studied hydrocolloids except xanthan gum aqueous solutions. The temperature had an opposite effect in comparison to one obtained for concentration dependencies; k decreased with temperature, while n increased. However, xanthan gum both in water and KCl exhibited a different patterns of the flow parameters dependencies on temperature, and provided some specific properties, such as relatively viscous solutions at higher temperatures, and a noticeable yield stress in the whole studied temperature range. The transition from double helical structure of the polysaccharides to single coil conformation in water and KCl aqueous solutions at 30 °C temperature was proved by the steep change of the Kraemer constant temperature dependence.
Keywords: Hydrocolloids, Flow behaviour, Flow parameters, Intrinsic viscosity, Kraemer constant
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1.INTRODUCTION
In the recent years, many studies have reported on the functional aspects of hydrocolloids and their application within food systems. Many hydrocolloids are widely used in the food industry to extend food shelf life, improve rheological properties of food products and encapsulate flavour compounds. The principal reason for the extensive use of hydrocolloids in the food industry is their ability to bind with water and to modify the properties of food ingredients[1-4].
From a chemical point of view, the hydrocolloids are mainly polysaccharides obtained from different sources. They are present in various parts of edible plants (starch, guar gum), of algae (carrageenan), of fungi and microorganisms (xanthan gum)[5,6]. Food hydrocolloids are a diverse group of long-chain polymers that are readily dispersive, fully or partially soluble, and prone to swell in water. They change the physical properties of the solutions to form gels or enable thickening, emulsification, coating, and stabilization; although the hydrocolloids are usually...