Characterization of pumpkin (Cucumis moschata, Duch.) tissue by stepwise-turgor pressure modification

DE ESCALADA PLA M ; DEBLON M; WIDER M; ROJAS AM,; GERSCHENSON LN

Valparaíso

Congreso; IV Congreso Iberoamericano de Ingeniería de Alimentos; 2003

Instituto Chileno de Ingeniería para Alimentos A.G.; Universidad Técnica Federico Santa María

Mechanical behaviour of vegetal tissues lies in a mechanical unit constituted by cell wall, plasmalemma and middle lamella. This work was undertaken for characterizing mechanical behaviour of pumpkin as a previous step for future technological applications. Raw tissue of pumpkin (Cucumis moschata, Duch) was characterized rheologically after a stepwise adjustment of its turgor pressure by immersion of tissue cylinders in buffered 0.00-1.20 M polyethylene glycol 400 (PEG) solutions. Compressions until fracture and relaxation curves were recorded through an Instron Machine, and frequency sweeps were performed with a Paar Physica rheometer working in the linearity range (0.01%-strain). Chemical analyses of the cell wall (CW)-middle lamellae (ML) polymers as well as activities of enzymes related to the CW were performed. Firmness, relaxation and dynamic parameters were higher at the highest turgor pressure including isotonicity. Peaks of failure were detected after compression at all osmotic conditions were CW-integrity was observed. It was determined that pectins located in CW were mainly water and CDTA extractable which would be accounting for the relative weakness of pumpkin tissue when cooked in boiling water. Ionically-bound POX activity ran in parallel to CW-stretching degree in soaked tissue. Just as lignification was not found, the role of ionically-bound POX would include cross-linking of hydroxyproline-rich wall glycoproteins located in the CW-matrix of mature pumpkin tissue, since ferulic acid moieties were not detected in this tissue. It was observed that CW of uncooked-pumpkin was specially resistant to the elongation under the hydrostatic pressure of the cell content. Taking into account the chemical CW analysis, this resistance would only be ascribed to the cellulose-(xyloglucan/extensin) framework of the uncooked tissue.