Contributions of cellular components to the rheological behaviour of kiwifruit

In this research work we propose an empirical model and develop a methodolo gy for the determination of the magnitude of the contributions of turgor pr essure. 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. Hay ward). Samples were equilibrated in a series (0-0.96 M) of polyethylene gly col 400 (PEG) solutions, and the volumes, storage (G') and loss (G") moduli , and the tangent of the phase angle (tans) of the tissue samples determine d, Tissue specimens were also examined using cryoscanning electron microsco py (cryo-SEM) to seek support for the rheological evidence obtained. The mo del proposed and the methodology applied allowed us to establish that the c omplex modulus (G*) of ripe and unripe raw outer pericarp kiwifruit tissue was influenced mostly by turgor pressure and cell wail rigidity. The loss o f middle lamellae during ripening was accompanied by a rigidification of th e cell wall. :(C) 2001 Elsevier Science Ltd. All rights reserved.