Cell wall hydrolases and amylase in kiwifruit softening

The activities of amylase, B-galactosidase (B-GAL), polygalacturonase (PG), and endo- 1,4- p-glucanase (EG), and ethylene evolution, were measured during ripening in kiwifruit (Actinidiu deliciosu (A.Chev.) (C.F. Liang et A.R. Ferguson var deliciosa, cv. Hayward). Fruit, harvested at firmness values (FV) of 65 N and a soluble solid (SS) content of 9%. were maintained in air at 2O’C for 40 days, until they reached the edible stage. Fruit firmness decreased throughout the experimental period and the lowest FV (about 5 N) was reached after 38 days of storage. SS content increased rapidly to about 13% within 15 days, then the rate of accumulation slowed and the SS content of 14.1% was reached after 33 days. Ethylene climacteric was a late event occurring af a FV of 10 N. The highest amylase activity was measured at harvest. During storage it declined, although a slight rise was detected at 33 days. B-GAL activity was vep low at the beginning of storage and increased throughout the experimental period, while PG activity was detected only after the fruit FV was below 10 N. EG activity decreased within the first three days of storage, then increased and peaked 15 days after harvest. Later, EG activity remained low but increased again at the end of the storage period. Application of propylene (500 ppm) to fruit that had softened to 30 N in air stimulated fruit softening and EG activity, and induced the accumulation of an EG-related peptide: the other enzymes appeared not to be affected by the gas.