Contributions of cellular components to the rheological behaviour of kiwifruit

Abstract

In this research work we propose an empirical model and develop a methodology for the determination of the magnitude of the contributions of turgor pressure, cell wall and middle lamellae, to the elastic properties of a plant material within a particular tissue type. The model system used was outer pericarp tissue from unripe and ripe kiwifruit (Actinidia deliciosa cv. Hayward). Samples were equilibrated in a series (0–0.96 M) of polyethylene glycol 400 (PEG) solutions, and the volumes, storage (G′) and loss (G″) moduli, and the tangent of the phase angle (tanδ) of the tissue samples determined. Tissue specimens were also examined using cryo-scanning electron microscopy (cryo-SEM) to seek support for the rheological evidence obtained. The model proposed and the methodology applied allowed us to establish that the complex modulus (G*) of ripe and unripe raw outer pericarp kiwifruit tissue was influenced mostly by turgor pressure and cell wall rigidity. The loss of middle lamellae during ripening was accompanied by a rigidification of the cell wall.