Starch Gelatinization under Shearless and Shear Conditions

Abstract

This article reviews the development of studying starch gelatinization under shear and shearless conditions, in particular the technologies used to detect the degree of gelatinization. Advantages and disadvantages of each technology were discussed and then some examples were presented to demonstrate their application. A new technology RheoScope, an instrument that can measure viscosity under shear stress and simultaneously observes variation of starch particles using a microscope, was also introduced. It was found the definition of "gelatinization" could be different for different detection technologies. Under shearless condition full gelatinization of starch needs about ratio of water 3/starch 1, while the gelatinization under shear condition requires less water content since shear stress enhances the processing. The number of endotherm and enthalpy of gelatinization depends on amylose/amylopectin, moisture and lipid content.

Effects of Incorporating Polycaprolactone and Flax Fiber into Glycerol-Plasticized Pea Starch

“…However, starch destructurization in this case of limited water took place at higher temperature than that in the case of excess water and was indeed facilitated by the induced shear stresses (Xie et al 2006). In addition to playing the role of a plasticizer, glycerol is capable of effecting starch gelatinization but the onset temperature of gelatinization is higher with decrease in water content (Nashed et al 2003).…”

“…In a more detailed and comprehensive way, the mechanism of gelatinization has been broken down into some phases (Xie et al 2006). The first phase involves gradual and reversible granule absorption of water with water mobility decreasing as the temperature increases from 20 to 60°C.…”

Extrusion processing and characterization of edible starch films with different amylose contents

“…Gelose 50 and Gelose 80) is crucial as it can significantly reduce instability in the extrusion process, and alleviate blockage in the extruder and die. Starch granules with less locally available water need a higher shear stress to assist gelatinization (Wang et al, 2010;Xie et al, 2006Xie et al, , 2008Xue et al, 2008). Premixing and equilibration allow water to diffuse into the starch granules and to distribute well in a system, resulting in a homogenous process of gelatinization, melting, and fragmentation of the starch during extrusion (Lai and Kokini, 1991).…”

Recent Processing Methods for Preparing Starch‐based Bioproducts

“…The food industry has long used extrusion to prepare ready-to-eat cereal snacks as well as animal feeds (Guy, 2001 ;Harper, 1978 ;Mercier et al ., 1989 ;Riaz, 2000 ). Much of the research on starch extrusion has been conducted to understand the structural changes and properties of starch in such systems (Akdogan, 1999 ;Barsby et al ., 2002 ;Colonna et al ., 1987 ;Lai and Kokini, 1991 ;Liu et al ., 2009 ;Wolf, 2010 ;Xie et al ., 2006a ). More recently, interest has focused on rates of digestibility due to relationships to nutrition and disease (Björck and Asp, 1983 ;Sajilata et al ., 2006 ;Singh et al ., 2010 ;Svihus et al ., 2005 ).…”

“…At high extrusion temperatures, starch becomes completely amorphous, although amylose-lipid V-type complexes often form on cooling, since these complexes crystallize rather rapidly. Increasing screw speed, and hence shear (or SME), has also been found to increase the extent of starch gelatinization or melting (Xie et al ., 2006a ). Increasing pressure has been found to decrease the melting temperature of starch in water at a rate of 0.075 °C/MPa (Douzals et al ., 2001 ).…”