Chemical and biochemical changes of pumpkin (Cucumis moschata, Duch.) tissue in relation to osmotic stress.

DE ESCALADA PLÁ M., PONCE N.M.A., WIDER M.E., STORTZ C.A., ROJAS A.M. Y GERSCHENSON L.N.

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE

John Wiley & Sons Ltd., publica para The Society of Chemical Industry (SCI).

Lugar: Baffins Lane, Chichester, Sussex PO19 1UD, England.; Año: 2005 vol. 85 p. 1852 - 1860

0022-5142

ABSTRACT             Chemical and biochemical changes of pumpkin (Cucumis moschata, Duch.) tissue in relation to osmotic stress were studied and related to tissue textural behavior. Turgor pressure of raw tissue was adjusted by immersion in hypotonic (0.0 mol m-3), isotonic (250 mol m-3) and plasmolyzing (1050 mol m-3) buffered (20 mol m-3 potassium phosphate, pH 6.8) solutions of polyethylene glycol 400 (PEG). It was determined that an important proportion of polysaccharides located in the cell wall (CW)-middle lamellae (ML) of studied tissue was water extractable. This proportion decreased when CW-stretch increased. Ionically-bound peroxydase (POX) presented an increased activity in swelled and isotonic tissue, probably associated to oxidative cross-linking of extensin located in the CW of this tissue, as a response to stress promoted by cut, immersion and turgor pressure change. The resistance of CW to elongation when equilibrated in hypotonic medium, might be ascribed to reinforcement of the CW by the oxidative cross-linking of extensin, with simultaneous formation of pectin-in-extensin entanglements. Plasmolyzed tissue where CW is relaxed, showed pectin-rhamnogalacturonan degradation. Water soluble fraction (WSF) showed to be a negative function of CW stretching and infinite force of relaxation.