Effects of Wax Treatment on the Physiology and Cellular Structure of Harvested Pineapple during Cold Storage

Pineapple (Ananas comosus (L.) Merr. cv. 'Paris') is sensitive to low temperature and highly susceptible to blackheart during cold storage, which causes serious fruit decay. This work investigated the effect of wax treatment (Sta-Fresh 2952, 60 g/L) on blackheart of pineapple under chilling stress. Wax treatment significantly reduced blackheart symptoms after 14 days of storage and markedly delayed changes in firmness and flesh color during the whole period of storage. The weight loss of wax-treated fruit (2.6%) was less than the control (3.1%) at the 24th day of storage. The treatment decreased the activities of PG and EGase for maintaining cell wall stability during the later period of storage. In the control fruit, the structure of flesh cells was significantly damaged under chilling stress, with looser cell wall, absence of middle lamella, loss of membrane integrity, and many cells near the vascular tissue collapsed. The subcellular elements could be barely observed in the control after storage. These destructive symptoms were significantly alleviated in the wax-treated fruit. The results suggest that wax treatment could reduce blackheart of pineapple under chilling stress via maintenance of cell integrity.