Two-Dimensional Tension Tests in Plant Biomechanics - Sweet Cherry Fruit Skin as a Model System

Abstract

Splitting of fruits is a function of two-dimensional tension caused by different growth rates of tissues and turgor, especially water uptake shortly before harvest. In order to analyse the mechanical properties of spheroid plant material close to stress-strain conditions in vivo, a new hydraulic two-dimensional testing device was set up. Sweet cherry (Prunus avium L.) fruit skin was chosen as a model system. The recorded pressure-deflection curves were non-linear, with a considerable initial “lag phase” and a distinct increasing end part. Taking into account the special geometry, these curves could be modelled with a newly developed analytical approach based on linear elastic material behaviour. The results demonstrated good correlation if a modulus of elasticity ranging from 160 to 250 MPa for the cherry fruit skin was chosen. In addition, a mean strength value of 47 MPa was calculated based on the theory of thin shells and spheres. The results are compared with mechanical data found for fruits and other plant material. In order to test the theoretical approach, two- and one-dimensional tension tests were performed on packaging PE foil, revealing a mean modulus of 171 MPa in bi-axial tension, and 193 and 242 MPa in uni-axial tension, depending on the test speed. The results demonstrate that it seems to be feasible to use this method to analyse the two-dimensional stress-strain conditions of spheroid plant materials such as cherry fruit skins. It may be applied as a tool for crop testing to elucidate the mechanical basis of cracking susceptibility of fruits.

Key words

Sweet cherry (Prunus avium L.) - fruit skin - biomechanics - two-dimensional tension testing - mechanical properties - splitting

References

• 1 Batal K. M., Weigele J. L., Foley D. C.. Relation of stress-strain properties of tomato skin to cracking of tomato fruit.  HortScience. (1970);  5 223-224
• 2 Bewley J. D., Banik M., Bourgault R., Feurtado J. A., Toorop P., Hilhorst H. W. M.. Endo-β-mannanase activity increases in the skin and outer pericarp of tomato fruits during ripening.  Journal of Experimental Botany. (2000);  51 529-538
• 3 Beyer M., Knoche M.. Studies on water transport through the sweet cherry fruit surface: V. Conductance for water uptake.  Journal of the American Society for Horticultural Science. (2002);  127 325-332
• 4 Carpita C., Gibeaut D. M.. Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth.  The Plant Journal. (1993);  3 1-30
• 5 Chanliaud E., Burrows K. M., Jeronimidis G., Gidley M. J.. Mechanical properties of primary plant cell wall analogues.  Planta. (2002);  215 989-996
• 6 Christensen J. V.. Cracking of cherries. IV. Physiological studies of the mechanism of cracking.  Acta Agriculturae Scandinavica. (1972);  22 153-162
• 7 Christensen J. V.. Cracking in cherries. VII. Cracking susceptibility in relation to fruit size and firmness.  Acta Agricultrae Scandinavica. (1975);  25 11-13
• 8 Cline J. A., Sekse L., Meland M., Webster A. D.. Rain-induced fruit cracking of sweet cherries. I. Influence of cultivar and rootstock on fruit water absorption, cracking and quality.  Acta Agriculturae Scandinavica B. (1995);  45 213-223
• 9 Considine J., Brown K.. Physical aspects of fruit growth.  Plant Physiology. (1981);  68 371-376
• 10 Cowie J. M. G.. Polymers: Chemistry and Physics of Modern Materials. London, New York; Blackie Academic and Professional (1991): 242-245
• 11 Dealy J. M.. Extentional rheometers for molten polymers - a review.  Journal of Non-Newtonian Fluid Mechanics. (1978);  4 9-21
• 12 Dobraszczyk B. J., Vincent J. F. V.. Measurement of mechanical properties of food materials in relation to texture: The materials approach. Rosenthal A. J., ed. Food Texture - Measurements and Perception. Gaithersburgh; Aspen (1999): 99-151
• 13 Glenn G. M., Pooviah B. W.. Cuticular properties and postharvest calcium applications influence cracking of sweet cherries.  Journal of the American Society for Horticultural Science. (1989);  114 781-788
• 14 Hankinson B., Rao V. N. M.. Histological and physical behaviour of tomato skins susceptible to cracking.  Journal of the American Society for Horticultural Science. (1979);  105 577-581
• 15 Hejnowicz Z., Sievers A.. Tissue stresses in organs of herbaceous plants III. Elastic properties of the tissues of sunflower hypocotyl and origin of tissue stresses.  Journal of Experimental Botany. (1996);  47 519-528
• 16 Lane W. D., Meheriuk M., McKenzie D. L.. Fruit cracking of a susceptible, an intermediate, and a resistant sweet cherry cultivar.  HortScience. (2000);  35 239-242
• 17 Lustig I., Bernstein Z.. Determination of the mechanical properties of the grape berry skin by hydraulic measurements.  Scientia Horticulturae. (1985);  25 279-286
• 18 Neinhuis C., Edelmann H.. Methanol as a rapid fixative for the investigation of plant surfaces by SEM.  Journal of Microscopy. (1996);  184 14-16
• 19 Nielsen L. E., Landel R. F.. Mechanical Properties of Polymers and Composites, 2nd ed. New York; Marcel Dekker (1994)
• 20 Niklas K. J.. Plant Biomechanics: An Engineering Approach to Plant Form and Function. Chicago; University of Chicago Press (1992)
• 21 Niklas K. J., Paolillo D. J.. Preferential states of longitudinal tension in the outer tissues of Taraxacum officinale (Asteraceae) peduncles.  American Journal of Botany. (1998);  85 1068-1081
• 22 Orfila C., Huisman M. M. H., Willats W. G. T., van Alebeek G., Schols H. A., Seymour G. B., Knox J. P.. Altered cell wall disassembly during ripening of Cnr tomato fruit: implications for cell adhesion and fruit softening.  Planta. (2002);  215 440-447
• 23 Papula L.. Mathematische Formelsammlung, 8th ed. Wiesbaden; Vieweg (2003): 38
• 24 Sekse L.. Cuticular fracturing in fruits of sweet cherry (Prunus avium L.) resulting from changing soil water contents.  Journal of Horticultural Science. (1995 a);  70 631-635
• 25 Sekse L.. Fruit cracking in sweet cherries (Prunus avium L.). Some physiological aspects - a mini review.  Scientia Horticulturae. (1995 b);  63 135-141
• 26 Shadwick R. E.. Soft composites. Vincent J. F. V., ed. Biomechanics - Materials. A Practical Approach. Oxford; IRL Press at Oxford University Press (1992): 133-164
• 27 Tonelli A. E., Srinivasarao M.. Polymers From the Inside Out - An Introduction to Macromolecules. New York; Wiley (2001): 189-195
• 28 Toole G. A., Gunning P. A., Parker M. L., Smith A. C., Waldron K. W.. Fracture mechanics of the cell wall of Chara corallina. .  Planta. (2001);  212 606-611
• 29 Vincent J. F. V.. Fracture properties of plants. Callow J. A., ed. Advances in Botanical Research 17. London; Academic Press (1990 a): 235-287
• 30 Vincent J. F. V.. Structural Biomaterials. London; Princeton University Press (1990 b)
• 31 Vincent J. F. V.. Strength and fracture of grasses.  Journal of Material Science. (1991);  26 1947-1950
• 32 Vincent J. F. V.. Plants. Vincent, J. F. V., ed. Biomechanics - Materials. A Practical Approach. Oxford; IRL Press at Oxford University Press (1992): 278-279
• 33 Voisey P. W., Lyall L. H.. Methods of determining the strenght of tomato skins in relation to fruit cracking.  Proceedings of the American Society for Horticultural Science. (1965);  86 597-609
• 34 Voisey P. W., Lyall L. H., Kloek M.. Tomato skin strength - its measurement and relation to cracking.  Journal of the American Society for Horticultural Science. (1970);  95 485-488
• 35 Whorlow R. W.. Rheological Techniques. New York, London; Ellis Horwood (1992): 265-274
• 36 Wiedemann P., Neinhuis C.. Biomechanics of isolated plant cuticles.  Botanica Acta. (1998);  111 28-34
• 37 Wittenburg J.. Mechanik fester Körper. Czichos H., ed. Hütte - Die Grundlagen der Ingenieurwissenschaften. Berlin; Springer (1989): E1-E119
• 38 Yamamoto T., Hosoi K., Watanabe S.. Relationship between the degree of fruit cracking of sweet cherries and the distribution of surface stress of the fruit analyzed by a newly developed system.  Journal of the Japanese Society for Horticultural Science. (1990);  59 509-517
• 39 Young W. C., Budynas R. G.. Roark's Formulas for Stress and Strain, 7th ed. New York; McGraw-Hill (2002): 553-688

Section Editor: G. Thiel