Fruit Softening I. Changes in Cell Wall Composition and endo-Polygalacturonase in Ripening Pears

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Abstract
Softening of pome fruits during ripening is characterized by the solubilization of pectin. The activity of endo-polygalacturonase (endo-PG, EC 3.2.1.15) was determined in pears (Pyrus communis L.) ripened at 18 °C, after storage at −1°C. The enzyme was assayed, using viscometry, in the presence of pectinesterase (EC 3.1.1.11) with citrus pectin as substrate. Endo-PG activity was not detected in fruit assayed immediately from store at −1 °C but the enzyme was present after 2 d at 18 °C when the fruit had started to soften and degradation of soluble pectin was apparent.