RETARDATION OF RIPENING AND DEVELOPMENT OF WATER STRESS IN PAPAYA FRUIT SEAL-PACKAGED WITH POLYETHYLENE FILM

The relationship between the effect of seal-packaging of papaya fruit cv. Backcross Solo with polyethylene film on ripening, development of water stress in the fruit tissues and modification of both the internal and external (in-package) atmospheres was investigated. Seal-packaging retarded the development of peel colour as well as reduced the increase in titratable acidity during ripening at 24 to 28°C. Fruit softening also was retarded, and this was attributable partly to decrease both in polygalacturonase (PG) activity and in polyuronide solubilization but the loss of insoluble polyuronides was not affected by the treatment. PG appeared to be not the only enzyme involved in the apparently extensive modification of the wall pectin.

Gradient in water deficit which paralleled the known gradient in tissue softness and PG activity, occurs in the mesocarp tissues of the papaya fruit. Besides ripening, seal-packaging also retarded the development of water stress in the fruit tissues as well as modifying both the internal and external atmospheres. As a whole, it appears that a substantial reduction in internal O₂ and a concomitant decrease in internal ethylene concentration may be instrumental in delaying ripening of the sealed fruit.