Desse, Mélinda (2008) From a swollen granule to a suspension : shear flow behaviour of a physically modified starch. PhD thesis Sciences et Génie des Matériaux, CEMEF - Centre de Mise en Forme des Matériaux, ENSMP p.240.

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Abstract

Starch used as a food thickener is interesting for its nutritional value but also because it offers better flavour perception when compared to other food thickeners such as hydrocolloids. This latter property seems to be linked to the ability of the product to mix in the mouth and thus to the diffusion of the tastants to the receptors. A suggested parameter that could reflect the ability to mix in the mouth and allow differentiating food thickeners is the break-up of a droplet submitted to simple shear. The aim of this study is to understand the behaviour of a swollen-in-water starch suspension droplet and compare it to the behaviour of a known fluid droplet, an aqueous solution of hydroxypropylmethyl cellulose (HPMC). The droplets placed in an immiscible fluid (silicon oil) are submitted to a simple shear flow using a counter rotating shear cell. The break-up conditions of a starch suspension droplet are studied in detail and compared to the HPMC solution droplet. The break-up mechanism of the suspension droplet is different from that of the HPMC solution droplet. The deformation of the suspension droplet was explained by the rheological behaviour of the suspension and the deformation of a single swollen starch granule submitted to shear.

Table of content

Table of Content

Abstract

Résumé français

Chapter I: Introduction

I.1 Motivation for the study

I.2. Experimental approach

I.3. Organisation of the thesis.

Reference List

Chapter II: Scientific background

II.1 Flavour perception

II.1.1 General aspects of flavour and its perception

II.1.2 Influence of viscosity and texture on flavour perception

II.1.3 Differences induced by the type of hydrocolloid/thickener

II.2 Starch: a complicated matter

II.2.1. Starch structure

II.2.1.1.The glucose unit

II.2.1.2.Amylose

II.2.1.3.Amylopectin.

II.2.1.4.Semi-crystalline structure and location of amylose and amylopectin within the granule

II.1.2.5.Small components in starch granules.

II.2.2. Starch in water: swelling and gelatinization process

II.2.3. Starch under mechanical stress

II.2.3.1 Behaviour of a single swollen starch granule

II.2.3.2 Rheological characterisation of starch pastes

II.2.3.3 The rheology of modified/cross-linked waxy maize (CLWM)

II.2.4. Conclusions

II.3 Droplet deformation

II.3.1 A few definitions and models

II.3.2 Newtonian systems

II.3.3 Non- Newtonian systems

II.3.4 When the dispersed droplet is a suspension

II.3.5. Conclusions on droplet deformation and break-up

II.4. Conclusions for Chapter 2

Reference List

Chapter III: Materials and methods

III.1. Materials: Their characterisation and sample preparation

III.1.1. Starch.

III.1.1.1. Starch characterisation.

III.1.1.2. Preparation of starch suspensions

III.1.1.3. Preparation of the continuous phase

III.1.2. Linear polymer solution: Hydroxypropylmethyl cellulose

III.1.2.1. Molecular structure and general information

III.1.2.2. Sample preparation

III.1.3. PolyDimethylSiloxane

III.1.3.1. Choice of suspending fluid

III.1.3.2. Flow properties of PDMS

III.2. Methods

III.2.1 Rheo-optics

III.2.1.1. Description of the counter rotating shear cell

III.2.1.2. Principle

III.2.1.3. Sample loading

III.2.1.4. Experimental conditions

III.2.1.5. Estimation of the error occurring during experimental settings

III.2.1.6. Analysis of droplet deformation experiments and orientation angle

III.2.2 Experimental procedures and devices used for rheological characterisation

III.2.2.1. Flow properties

III.2.2.2 Oscillatory mode

III.2.2.3 Low viscosity fluids: starch suspension supernatant

III.2.3 Interfacial tension

III.2.4 Differential Scanning Calorimetry

III.2.5 Size Exclusion Chromatography coupled to Multi-Angle Laser Light Scattering (SECMALLS)

III.2.6 Analytical Ultracentrifugation AUC

III.2.7 Design and statistical analysis of centrifugation influence on supernatant properties..

III.2.8. Iodine staining: amylose/amylopectin determination

III.2.9. Atomic Force Microscopy (AFM)

III.2.10. Scanning Electron Microscopy (SEM)

III.2.11. Density measurements.

III.3. Conclusions for Chapter 3

Reference List

Chapter IV: Surface properties of starch granules and their behaviour under flow

IV.1. Shape, size and surface properties of granules: modified waxy maize and potato

IV.1.1. Shape of the granules

IV.1.2. Surface roughness assessment using AFM

IV.1.3. Conclusions

IV.2. Behaviour of a single granule under flow

IV.2.1 Dry starch granules

IV.2.1.1. Rotation of a solid sphere: Jeffery’s law

IV.2.1.2. Rotation of starch granules submitted to simple shear

IV.2.2. Swollen in water starch granules.

IV.2.2.1. Deformation of the granule and ejection of solvent

IV.2.3. Conclusions

IV.3. Conclusions for Chapter 4

Reference List

Chapter V: Properties of the starch suspension

V.1. Rheological study of a starch suspension

V.1.1. Suspension at maximum average swelling and at theoretical volume fraction of 1

V.1.1.1. Influence of geometry

V.1.1.2. Optimization of the measurements

V.1.1.3. Description of the flow curve

V.1.1.4. Time dependence: thixotropic/antithixotropic behaviour

V.1.1.5. First normal stress difference

V.1.1.6. Viscoelasticity of the suspension

V.1.2. Influence of starch concentration on suspension behaviour

V.1.2.1. Flow behaviour of suspensions with a volume fraction below 1

V.1.2.2. Effect of starch concentration above close packing volume fraction on flow behaviour and yield stress

V.1.2.3. Evolution of viscoelastic properties with starch concentration

V.1.3. Conclusions

V.2. Analysis of the continuous phase of a starch suspension

V.2.1. Surface tension

V.2.2. Statistical analysis

V.2.3. Differential Scanning Calorimetry

V.2.4. Iodine staining

V.2.5. Size Exclusion Chromatography coupled to Multi-Angle Laser Light Scattering and Analytical Ultracentrifugation

V.2.6. Discussion

V.2.7. Conclusions

V.3. Conclusions for Chapter 5

Reference List

Chapter VI: Shear induced deformation and break-up of a starch suspension

droplet: comparison with a polymer solution

VI.1. Characterisation of the rheological behaviour and surface activity of Hydroxypropylmethyl Cellulose aqueous solution

VI.1.1. Flow and viscoelastic properties of HPMC solutions

VI.1.2. Surface and interfacial tension

VI.2. Shear induced droplet deformation and break-up

VI.2.1. Deformation of solution and suspension droplets

VI.2.1.1Visual observation of droplets at different concentrations

VI.2.2.2.Comparison between the physico-chemical aspects of a starch suspension and an HPMC solution

VI.2.2.3. Droplet orientation

VI.2.2.4. Droplet deformation

VI.2.2.5. Droplet relaxation

VI.2.2. Break-up condition of a droplet of starch suspension

VI.3. Conclusion for Chapter

Reference List

Chapter VII: Conclusions & Future work.

VII.1.Results and Interpretation

VII.2. Suggestions for further research

VII.3. Suggestion for possible industrial applications

Reference list:

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