Table grapes are subject to serious water loss and decay while making the long trip from the vine to tables around the world. Mold and browning of the stems are the two main factors that reduce grape quality during shipping and storage in retail produce sections.
Pads placed over the fruit packed in boxes are one way of ensuring that consumers get fresh, appealing fruits. The pads release sulfur dioxide, or SO2 , a chemical used to prevent mold and decaying of table grapes. Sulfur dioxide as a method of controlling decay has been in use for over 75 years. Since the late 1960s, grape producers and packers have favored use of a dual-release pad, which can keep grapes from decaying for extended periods.
Two methods are presently used for transporting the packed grapes. One method is to place a perforated plastic liner inside each box, put the grapes in the liner, and then cool. The the other method is to cool the boxed grapes and then externally wrap the entire pallet of boxes. In both cases, a SO2 pad is placed in each box.
Researchers in the Department of Postharvest Science at the Agricultural Research Organization of Israel's Volcani Center recently compared both packing methods for their efficiency in maintaining grape quality and preventing decay for periods ranging from 33 to 117 days. The experiments included 'Redglobe' and 'Zainy' grapes packaged in plastic boxes and 'Thompson Seedless' grapes packaged in cardboard boxes.
The study concluded that the quality of the grapes in the trials with plastic boxes was either similar in both packaging methods or better in the wrapped pallet than the liner method. Prevention of decay was also better with the wrapped pallets than for storage in liners. In the experiment with cardboard boxes, however, the externally wrapped boxes contained lower levels of SO2, probably because the cardboard absorbed more SO2, and the grapes developed more decay than when perforated liners were used.
Although the most commonly used method of grape packaging for long-distance shipment is the use of perforated liners, the study proved using external wrapping of pallets with low-density polyethylene film can be as effective as the liner method in preventing grape decay. The external wrapping method has significant advantages over the use of box liners: it allows faster precooling of grapes and is more economical than using individual liners. The pallet wrapping method works best when used with recyclable plastic boxes, as the plastic boxes do not absorb the SO2. A bonus for the environmentally conscious industry: plastic boxes also can be more environmentally viable than traditional cardboard boxes.
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