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The activities of several cell wall-associated enzymes of the outer pericarp were assayed during softening of kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Hayward] treated with ethylene. The activity of polygalacturonase (EC 3.2.1.15) increased slightly during fruit softening, while β-galactosidase (EC 3.2.1.23) activity remained constant. Salt-extracted pectinesterase (EC 3.1.1.11) activity increased during ethylene treatment, then dropped rapidly to low levels as fruit softened. Residual pectinesterase activity, extracted after digestion of the cell wall pellet with a fungal enzyme mix, decreased on softening. The rapid softening of kiwifruit in response to ethylene treatment may be initiated by an induction of pectinesterase activity, causing increased de-esterification of cell wall pectins, followed by degradation of solubilized pectin.
In an effort to develop an inexpensive alternative to vapor-heat insect disinfestation of `Kensington' mango (Mangifera indica Linn.), the effect of postharvest hot water treatments (HWT) on fruit quality was determined. Fruit were given 46C HWT for 30 minutes at a fruit core temperature of 45C either 24 hours after harvest or after various conditioning treatments of 4 to 24 hours at 39 ± 1C in air. Fruit were compared to nontreated fruit after a subsequent 7 days at 22C. The HWT increased fruit softening and reduced chlorophyll fluorescence and disease incidence. The longer conditioning times produced softer fruit. Conditioning reduced damage to the fruit caused by HWT. Preconditioning for ≥8 hours resulted in <1% of fruit being damaged as shown by cavities, skin scald, and starch layer formation. The quantitatively measured higher mesocarp starch content paralleled the visible starch layer injury. Skin yellowing increased in response to HWTs that were not damaging to the fruit. Fruit ripening changes were unequally affected by HWT and by conditioning before HWT; thus, the sequence and extent of these changes must be determined to establish a reliable and useful hot water disinfestation treatment.