TEXTURAL CHANGES DURING NECTARINE (PRUNUS-PERSICA) DEVELOPMENT, AND RIPENING

Changes in nectarine (Prunus persica (L.) Batsch var nectarina (Ait.) Maxim. cv. 'Fantasia') texture were measured during the last 10 weeks of fruit development before commercial maturity, and during ripening. Both tensile and compressive textural characteristics of mesocarp tiss ue were measured using an Instron Universal Testing Machine. Developme ntal fruit softening was primarily a consequence of cell expansion. On three occasions during the developmental series we compared changes i n texture during 3-5 days of postharvest storage at 20 degrees C with textural change dyer the same period on the tree, In the first-two per iods the fruit were not physiologically mature and harvested fruit did not undergo normal ripening. The distinctive patterns of change in te nsile and compressive properties-at these times were consistent with c hanges due to low turgor, as predicted by cellular theories, Harvested fruit from the third period (physiologically mature fruit producing e thylene at around 13 nmol kg(-1) h(-1)) showed an accelerated rate of ripening and softening compared with fruit left on the tree, Reduction s in cell wall strength and cell-to-cell adhesion would explain the ob served patterns of change in tensile and compressive properties of mat ure fruit, Scanning electron microscopy confirmed there was a change i n the predominant cause of tensile failure from cell rupture in immatu re fruit to cell separation in mature fruit. A tensile parameter which correlated with this change is described.