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Characterizing Starch Pasting with a Modular Compact Rheometer

Rheometers and viscometers are nowadays standard measurement devices for characterizing pasting behavior of starches. Appropriate viscosity measurements typically consist of different measuring intervals such as mixing, equilibration and water uptake, heating, holding, and cooling phases. Using an Anton Paar Modular Compact Rheometer (MCR) along with the tailor-made starch cell, and RheoCompass™ software allows easy viscosity measurements during the different phases, and automatic determination of relevant parameters, such as the pasting temperature.

Introduction

Starch is widely used in food industries due to its nutritional importance and physical properties. It is usually extracted, refined, and modified from seeds, roots and tubers before being mainly used as an additive for food processing, e.g. as thickener and stabilizer due to its ability to gelatinize and paste.

From a chemical point of view, starch is a polysaccharide composed of linked linear or branched glucose components. The linearly linked molecules are called amylose and the branched amylopectin. Native starch contains amylose and amylopectin packed in starch granules.

When exposing starch to water and heat, the starch gelatinizes and forms a paste, i.e. the granules start to swell above a critical temperature and, eventually, rupture. Amylose and amylopectin leaches into the fluid, forming a viscoelastic gel or paste with decreasing temperature. The extent of gelatinization and pasting ability depends on the nature of starch, its modification, as well as processing parameters such as temperature profiles and stirring speeds.

Standards have been created with well-defined mixing, heating, holding, and cooling phases to characterize the gelatinization and pasting behavior of starches. In the following tests, the pasting behavior is studied according to the ICC 162 standard.This standard is applicable for native and modified starches, flours, and cereal grains (after appropriate grinding) to analyze the pasting properties and study the effect of alpha-amylase on starch-water or flour-water suspensions during heating and cooling.

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