**1. Introduction**

Design of new food products is one of the most important tasks in the food industry. Improving or controlling texture of foodstuffs leads to products with advanced functionalities e.g. creation of nursing-care foods, ''ready-to swallow foods'', soft or hard gels etc. (Funami, 2011).

Texture change can be achieved by adding hydrocolloids that in small quantities bind large amounts of water and can then control both structure and texture. Starches belong to the same category of hydrocolloids, although they are used in a wide range of products either as raw materials or as food additives. Starches can differ with respect to the amylose content depending on their origin, or can be structurally modified. Native starches could have negative aspects such as gel syneresis, retrogradation, breakdown, cohesive, rubbery pastes and undesirable gels formation (Whistler & BeMiller, 1997), but this is not the case with modified starches. Moreover, modified food starches are less expensive and are more widely available than gums or other food stabilizers. A way to overcome shortcomings of native starches is their blending with polysaccharide hydrocolloids. Native or modified starches, and non-starch hydrocolloids are increasingly important ingredients in the modern health-conscious food industry (Techawipharat et al., 2008), considering that specific starch types such as resistant starch can be considered insoluble fibers as well.

This chapter aims at highlighting recent research in the field of viscoelastic properties of starches and their mixtures with some selected hydrocolloids. Furthermore, these interactions will be linked to the final rheological characteristics of specific products aimed at successful product development.

The control of texture in real foods with several ingredients can be achieved through viscoelasticity measurements of carbohydrate mixtures at low concentrations. This research

© 2012 Mandala, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

can result in new products development that aims at specific texture characteristics. Examples are focused on oscillatory experiments and in some case correlations to viscous properties are presented. The role of rheology in current research is further shown and discussed through these examples.

Viscoelastic Properties of Starch and Non-Starch Thickeners in Simple Mixtures or Model Food 219

typical of a liquid-like material. As frequency increases, G'(ω) crosses G''(ω), the response of the material beyond this cross-over frequency is said to be solid-like. Entanglements of macromolecular solutions can result in such behavior. When G' is higher than G'' over most of the frequency range investigated, a weak gel behavior is observed due to the formation of

Thus, viscoelastic structures of hydrocolloids may differ considerably. So, recent data about

Dynamic rheological tests allow continuous measurement of dynamic moduli during temperature and frequency sweep testing of a starch suspension. The rheological properties of starches differ, because their composition and granules' morphology is different. Thus, the identification of native starch sources is required in order to achieve the desired functionality and unique properties (Duxbury, 1989). Furthermore, concentration effects, temperature, heating rate and shear rate effects can be found and measured by rheological properties.

Concerning starch the following changes under heating can be measured using oscillatory

Retrogradation, which can be distinguished in short-term by network formation and

During this first stage of heating, starch granules swell during the process of gelatinization. Soluble polymer molecules leach from the swollen granules and the rheological properties, such as storage modulus (G') and loss modulus (G'') of the starch increase to a maximum. A

formation of three-dimensional (3D) gel network developed by leached out amylose and reinforced by strong interactions among swollen starch particles (Fig. 1). Similar changes

The swelling of the granules is important for both viscosity increase and viscoeleasticity of the produced dispersions. Granules' morphology and rigidity, complexes with other components (e.g. lipid-amylose), amylose content, protein content are some factors that determine both peak values of the viscoelastic parameters and their breakdown thereafter.

Concerning their botanical source, among native starches (corn, rice, wheat and potato), potato starches exhibit the highest swelling power and final viscoelastic values. Their shape and size differs with respect to starches of other botanical sources. Starch granules of potato are smooth-surfaced and of different shapes form oval and irregular to cube-shaped. Starch

C (Ahmed et al., 2008) caused by the

a weak three-dimensional network of ordered chain segments.

long-term retrogradation that lasts several weeks

**3.1. Dynamic rheology and gelatinization** 

sharp increase in G' may occur between 60-80°

can occur when viscosity is measured.

**3. Starch under heating** 

experiments.

 Gelatinization Pasting Gelling and

their behavior in mixtures with starch or model foods is discussed.
