Microstructure of Produce Degradation 553
18.6 STRATEGIES FOR FRUIT PRESERVATION AND
IMPROVED SHELF LIFESince fresh produce is shipped worldwide, the time for a product to reach the market
may be considerable. Cold storage and commodity-specific packaging is a typical
method of protection and preservation for many fruits and vegetables. Modified
atmosphere packaging and storage under controlled atmospheres [51] are also of
importance, particularly in the minimally processed food arena.
At the consumer level, water sprays to avoid dehydration combined with refrig-
eration is common practice in the supermarket. However, refrigeration simply slows
degradative processes and is often insufficient to meet the demands of today’s
marketing techniques. Therefore, other postharvest treatments are needed to further
increase storage life. Edible coatings, such as waxes, and those that also include
antibrowning agents form a semipermeable barrier to air to control respiration and
prolong shelf life [39,52]. Due to increasing concern about unacceptable residues
on fruit surfaces following chemical treatments, a number of chemical-free posthar-
vest techniques have been investigated to lengthen the storage life of fresh produce.
Postharvest heat treatment has been in commercial use for many years [53];
however, the technology is still being perfected for different commodities. Short hot
water rinses were investigated as a method of reducing postharvest losses of Galia
melon (cantaloupe) [54] and sweet pepper [55] fruits. Scanning electron microscopy
showed that the fruit surfaces were free of debris and fungal spores and that super-
ficial cracks in the epidermis were sealed. Observation of fresh orange bell pepper
revealed superficial cracks and debris on the surface (Figure 18.16a). Aging resulted
in collapse of mesocarp tissue (Figure 18.16b and c) just beneath the outer tissue
layers.
Hot water immersion was effective in disinfestation and in maintaining fruit
quality of Valencia oranges [56]. Light and electron microscopy showed that there
was little effect on surface waxes of the orange fruit as a result of heating. Mandarin
oranges were heat-treated for 3 min prior to storage at temperatures ranging from
50 to 58°C in the assessment of temperature effectiveness in storage performance.
Treated fruit surfaces were compared to control fruits by SEM observation. Heat
treatment of the mandarins at 50 to 54°C smoothed the waxy surface, which was
granular in the control, partly removed the wax at 56°C, and completely removed
the wax at 58°C [57]. Hot water brushing of organic citrus fruits reduced postharvest
decay and scanning electron microscopy showed that the epicuticular waxes had
been smoothed by the treatment and the cracks and stomata were sealed by the wax,
minimizing the sites of pathogen entry [58].
Heat treatment of mango was ineffective for heat-sensitive cultivars, in which
damage resulted from the heat treatment. Such heat-related injuries were investigated
using scanning and transmission electron microscopy where cuticle and exocarp
ruptured and exposed internal cells. Cell walls of the mesocarp were convoluted and
thickened and starch granules still remained in the tissue, suggesting that the car-
bohydrate metabolic enzymes had been activated [59].
Other nontoxic shelf-life extension methods include treatment with carbon diox-
ide followed by refrigerated storage. Firmness was increased and decay susceptibility