DMA THERMAL ANALYSIS OF PLANT TISSUE Jiří Blahovec

Thermal Analysis of Materials … developed out of the scientific study of the changes in the properties of a sample which occur on heating. Haines, 2002

BASIC THERMAL METHODS Differential scanning calorimetry DSC Differential thermal analysis DTA Thermomechanical analysis TMA Dynamic mechanical Analysis DMA Dielectric thermal analysis DETA Thermogravimetry TG … study of changes in structure and mechanisms …

HOW TO APPLY THEM TO BIOOBJECTS?

SIMPLE POTATO CELLULAR STRUCTURE Symplast Apoplast Cellular walls

SCHEME OF CELLULAR MEMBRANE Polar hydrophilic side Hydrophobic sides Lipid Double Layer symmetrical Pore – Based on Proteins source of asymmetry

COMPLICATED STRUCTURE caused COMPLICATED THERMAL RESPONSE

MECHANICAL PROPERTIES and cell walls

POTATO Compression at room temperature Squeezing out ~ 3 %

POTATO Slope analysis True slopes: I Variable, flaccid tissue II about 3 MPa, quasi-elastic III (1.54±0.13) MPa, sap squeezing out

TISSUE RIGIDITY

GOOD BASIS FOR DYNAMIC MECHANICAL ANALYSIS (DMA) OF VEGETABLE TISSUE

TYPES OF LOADING

DMA PARAMETERS Specimen dimensions: length 22 mm width 8 mm thickness 3 mm Distance between jaws 4.4 mm Amplitude 1 mm (it corresponds to 3 % quasi-elastic deformation) Frequency 1 Hz Temperature Range 30-90 oC Heating Rate 1 oC/min Tissues: Potato (cork, pith and side with vascular ring), Carrot Tests were done in air with 90 % humidity !

POTATO The important starch effect

STORAGE MODULUS

LOSS MODULUS

LOSS TANGENT (LM/SM)

STORAGE MODULUS (Slope Analysis – 10 replications)

LOSS MODULUS (Slope Analysis – 10 replications)

LOSS TANGENT (Slope Analysis – 10 replications)

POTATO PITH AND CORTEX AT ROOM TEMPERATURE (a) pith (b) cortex Starch grains Protein micelles Cell wall Arranged under Karlsson & Eliasson (2003), LWT 36, 735-741.

STARCH CHANGES First Heating POTATO STARCH CHANGES First Heating Arranged under Ratnayake & Jackson (2007) Carbohydrate Polymers 67, 511-529. Gelatinization Tissue DMA Peak

POTATO STARCH CHANGES Shear Rheology X-Ray Diffraction Arranged under Ratnayake & Jackson (2007) Carbohydrate Polymers 67, 511-529. Kaur et al. (2002), Food Chemistry 79, 183-192 Shear Rheology X-Ray Diffraction Partial Crystallinity Crystallinity (%) Nearly amorphous 10 45 Partial Crystallinity 45

POTATO STARCH CHANGES Swelling Arranged under Li & Yeh (2001) J. Food Eng. 50, 141-148

CARROT A representative of standard plant tissue

ELASTIC MODULE

ELASTIC MODULE (Slope Analysis – 10 replications) Indications of further temperature dependent changes

LOSS TANGENT (Slope Analysis – 10 replications) Indications of further temperature dependent changes

CONCLUSIONS Deformation of potato tubers at temperatures higher than 60oC is controlled by starch gelatinization and swelling, DMA detects gelatinization in state in which the thermally controlled processes detected by DSC are finished, DMA is able to detect further cell wall changes connected with cell wall semi-permeability

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