Effect of immersion and turgor pressure change on mechanical properties of pumpkin (Cucumis moschata, Duch.)

Abstract

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. Examinations using 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 m −3 ) a gain of tissue weight was observed, a trend that indicated a null occurrence of cell bursting as confirmed by observations using LM and TEM of undamaged cell membranes with swelled cytoplasms. However, no significative change in relative volume was detected for tissue equilibrated in PEG with concentrations of 0-130 mol m −3 , probably due to the resistance of CW to further elongation. Peaks of failure were observed during compression for tissue equilibrated under 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 the linear viscoelasticity range and dynamic assays provide analogous information concerning tissue behavior.

Pumpkin (Cucurbita moschata Duchesne ex Poiret) mesocarp tissue as a food matrix for supplying iron in a food product

“…Although forces were higher (70-90 N), deformations also increased ( Table 2). Similar behavior was reported previously by de Escalada Pla et al (2006) for plasmolysed pumpkin tissue; in that case, the cell membrane and cell wall integrity were observed, but the membrane was completely retracted and, so, firmness decreased with respect to the isotonic tissue due to higher deformation. In the present research, for storage times greater than three days, the water loss and solid gain determined tissue firmness practically equal to that observed previously to the addition of the osmotic solution.…”

Mechanical properties of sugar beet root during storage

“…This method has been used for the evaluation of fruit quality (de Escalada Pla et al, 2006;Forney, 2008;Harker et al, 2002;Ruiz et al, 2005;Wu and Abott, 2002). With this test, the maximal penetration force is measured that is required to let a cylindrical probe penetrate, e.g.…”

Influence of Cell Integrity on Textural Properties of Raw, High Pressure, and Thermally Processed Onions

“…The role of cellular structures in determining the mechanical properties of plant tissues (Donald and others 2003; de Escalada Pla and others 2006) and the effect that single cells have on textural properties of tissues are topics of current research interest (Wang and others 2006). Puncture tests, commonly used to analyze the texture of fruits and vegetables, measure the force and deformation required to push a probe into the product and in so doing cause failure to the tissue (Mohsenin 1986; Bourne 2002).…”