High-density Polyethylene Wrap Improves Wound Healing and Lengthens Shelf-life of Mechanically Harvested Grapefruit

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Abstract
Superficial scratches were a major problem in mechanically harvested ‘Marsh Seedless’ grapefruit (Citrus paradisi Macf.). Sealing individual fruit in 0.015 mm thick high-density polyethylene (HDPE) sheets greatly reduced fruit weight loss under uncontrolled room conditions. HDPE-wrapped fruit retained excellent external and internal qualities for 3 months, but was slightly softer and began to develop an unfresh off-flavor and external yellow-orange color during the 4th month of storage. HDPE wrap did not keep the injury scars invisible but improved active healing and inhibited further softening and spreading of scars, thus partly preserving fruit appearance. Highest phenylalanine ammonia-lyase (PAL) enzyme activity, a key process in lignification and wound healing, occurred in scratched, HDPE-wrapped fruit stored at 30°C. Peak activity was reached 72 hours following injury. Decay of scratched fruit by Penicillium digitatum Sacc. was reduced markedly by storage at low temperature (10°), by disinfection, or by wrapping in HDPE. The beneficial anti-decay effects of HDPE can be attributed both to insulation against secondary contact infections and to provision of a humid atmosphere which at warm temperature enhances lignification and the healing process of superficial flavedo scars.

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