1. THERMOMECHANICAL PROPERTIES OF VEGETABLE TISSUE AT 30-90 oC
Jiří Blahovec

2. STRUCTURE OF VEGETABLE TISSUE WITH STARCH (Demonstrated on potato tissue)

3. POTATO CELLULAR STRUCTURE
Cell Walls
Intracellular Content

4. CELL WALL MEMBRANE Lipid Double Layer Pore – Based on Proteins
Polar hydrophilic side
Hydrophobic sides
Lipid Double Layer
symmetrical
Pore – Based on Proteins
source of asymmetry

5. STARCH GRAINS Pukhraj, (b) Kufri Jyoti, (c) Kufri Badshah
Dimension, Shape & Composition: amylose x amylopectin
Pukhraj, (b) Kufri Jyoti, (c) Kufri Badshah
Kaur et al., Food Chemistry 2002

6. DIFFERENT TUBER PARTS AT ROOM TEMPERATURE
(a) pith (b) cortex
Starch grains
Protein micelles
Cell wall
Arranged under Karlsson & Eliasson (2003), LWT 36,

7. MECHANICAL PROPERTIES and cell walls

8. POTATO Deformation Curves in Compression at room temperature
Squeezing out
~ 3 %

9. POTATO Slopes of Deformation Curves Room Temperature
True slopes: I Variable, flaccid tissue II about 3 MPa, quasi-elastic III (1.54±0.13) MPa, squeezing out

10. DYNAMIC MECHANICAL ANALYSIS (DMA)

11. TYPES OF LOADING

12. DEFORMATION PARAMETERS
Specimen dimensions: length mm width mm thickness 3 mm Distance between jaws mm Amplitude mm Frequency Hz Temperature Range oC Heating Rate oC/min
Tuber tissue from cortex parenchyma Long axis of the specimen parallel to tuber axis

13. DEFORMATION PARTS
Part I Deformation of flaccid tissue (generally inelastic) Turgor pressure ≤ 0
Part II Quasi-elastic deformation Turgor pressure > Cell internal pressure ≤ critical stress for squeezing out of cellular sap water
Part III Mechanical dewatering (inelastic)

14. COMPLEX MODULUS OF ELASTICITY

15. COMPLEX MODULUS OF ELASTICITY Temperature Derivatives

16. COMPLEX MODULUS OF ELASTICITY Amplitude

17. COMPLEX MODULUS OF ELASTICITY Loss Tangent

18. ELECTRIC CONDUCTIVITY (Role of Temperature)
Personius, Sharp (1938)
Loss of cell wall semi-permeability

19. PARTIAL CONCLUSION
Mechanical and texture properties are controlled by properties of cell walls at least in part II of deformation curves at critical temperatures

20. STARCH GELATINIZATION IN POTATO DSC
Pith
Cortex
Stem End
Bud End

21. STARCH GELATINIZATION IN POTATO Combination of DSC and DMA

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

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

24. POTATO STARCH CHANGES Swelling
Arranged under Li & Yeh (2001) F. Food Eng. 50,

25. ROLE OF TEMPERATURE Depending on air humidity (drying level)
Under Nilsson et al. (1958), Physiologia Plantarum 11,
Depending on air humidity (drying level)
Solutions
Starch
Critical Temperature

26. CONCLUSIONS
Aftercritical deformation of potato tubers (i.e. at temperatures higher than 60oC) is controlled by starch gelatinization,
DMA detects gelatinization in state in which the thermally controlled processes detected by DSC are finished,

27. THANK FOR YOUR ATTENTION!