Turgor pressure in vegetable tissues: comparison of the performance of incipient plasmolysis technique using mannitol and polyethyleneglycol.

SAJNIN C., GERSCHENSON L.N. Y ROJAS A.M.

FOOD RESEARCH INTERNATIONAL

ELSEVIER Sci. Ltd.

Lugar: The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK.; Año: 1999 vol. 32 p. 531 - 537

0963-9969

Abstract: To determine turgor pressure of melon and kiwifruit edible parts (Cucumis melo, L. and Actinidia deliciosa, A. Chev., respectively), we measured volume change of tissue cylinders immersed in different mannitol or polyethylene glycol 400 (PEG) solutions up to equilibrium, and sought the osmotic potential that led to incipient plasmolysis. Compression tests were also performed to compare the mechanical response of these tissues at different turgor conditions. Cellular vitality was evaluated through fluorescein diacetate hydrolisis by lipases located in the active cellular membrane. This enzyme-catalyzed reaction was observed by fluorescence microscopy. Results indicated that turgor pressure of kiwifruit could only be evaluated by using PEG as a solute. Immersion in PEG solutions did not affect the mechanical response of this tissue `per se´ based on a comparison of tissue firmness. On the one hand turgor pressure values determined in melon samples were different using both solutes and on the other the immersion affected melon tissue because a significantly (P<0.05) higher firmness was obtained for raw (unsoaked) melon cylinders. Cellular membranes were not affected by mannitol or PEG shown by fluorescence microscopy of isotonic melon samples. Some solute-specific effect could change the water movement into the tissue affecting the value of melon turgor pressure finally estimated. Thus we emphasized the importance of using the same solute to compare the effect of different treatments and/or ripeness grade on turgor pressure when incipient plasmolysis technique is used. In this way, PEG showed to be a useful alternative solute due to its wide solubility range.