EFFECT OF IMMERSION AND TURGOR PRESSURE CHANGE ON MECHANICAL PROPERTIES OF PUMPKIN (Cucumis moschata, Duch.)

MARINA DE ESCALADA PLA; MARISA DELBON; ANA M. ROJAS; LÍA N. GERSCHENSON

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE

WILEY InterScience

Año: 2006 vol. 86 p. 2628 - 2637

0022-5142

Mesocarp raw tissue of a pumpkin (Cucumis moschata Duch) popularly known in Argentina as ?calabacita criolla? was rheologically characterized by large and small deformations after a stepwise adjustment of its turgor pressure to determine the relative contributions of turgor pressure, cell wall (CW) and middle lamella (ML) to the mechanical behavior. Microscopic observations (light microscopy, LM, and transmission electron microscopy, TEM) were performed in order to explain the textural behavior observed. In general, firmness at failure, residual relaxation force and dynamic moduli increased with turgor pressure. For all the hypotonic solutions (polyethylene glycol 400, PEG concentrations lower than 250 mol a gain of tissue-weight was observed, trend that indicated a null occurrence of cell bursting as confirmed by observation through LM and TEM of undamaged cell membranes with swelled cytoplasms. Anyhow, no significative change in relative volume was detected for tissue equilibrated in the 0-130 mol PEG concentration range probably due to CW resistance to further elongation. Peaks of failure were observed during compression for tissue equilibrated at all osmotic conditions and their presence was associated with CW-integrity. Plasmolysed tissue did not show a residual force at infinite time of relaxation. Incipient plasmolysis was better detected by rheological studies than by volume change and it was confirmed by LM. Significant correlations were obtained between residual relaxation force and either storage moduli or phase shift angle, revealing that relaxation out of linear viscoelasticity range and dynamic assays provide analogous information concerning tissue behavior.