Agriculture Reference
In-Depth Information
food supplies dwindle, Culinary Specialists resort to peeling away wilted, brown
leaves of lettuce and other salad greens to fi nd an edible portion. Thus, extending the
shelf life of FFVs shipboard is a high priority to ensure the availability of high-quality,
fresh, wholesome foods for consumers. As demonstrated in the test aboard the USS
Ronald Reagan mentioned earlier, MAP systems can retard postharvest quality losses
and extend the shelf life of iceberg lettuce, bananas, broccoli, and romaine lettuce.
The U.S. Navy estimates that implementing MAP systems will prevent premature
spoilage of FFVs shipboard and could achieve cost-savings of up to $10.6M over the
next 5 years.
MAP Technologies
The basic premise of MAP technology (Werner and Hotchkiss 2006) relies on under-
standing the fundamental nature of respiration. Minimally processed fruits and veg-
etables are living, respiring tissues that consume oxygen and release carbon dioxide,
water vapor, and heat through normal metabolic processes, with individual produce
types having different respiratory requirements. Modifying the atmosphere in which
the produce is stored can reduce the metabolic rate and prolong shelf life, maintain
postharvest quality, and retain nutritive content. The commercial MAP technology
used in the study onboard the USS Ronald Reagan was based on perforate membrane
substrate coated with a side chain crystallizable (scc) polymer (provided courtesy of
Apio, Inc, Guadalupe, CA). The properties of the membrane-scc polymer construct
can be adjusted to vary its gas permeability by changing the polymer composition,
the thickness of the scc coated on the polymer, and the number or diameter of holes
in the fi lm, and thereby accommodate different types of produce. In general, the ssc-
polymer membrane is designed to provide higher permeability rates than conventional
fresh produce packaging (Table 14.3 ).
The physical characteristics of the ssc polymer are temperature-dependent. At
higher temperatures, the ssc-coated membrane becomes more amorphous, which
imparts higher gas permeability by a phenomenon called
moderate temperature com-
pensation character
. In general, a temperature increase from 0-10 °C will induce an
increase in the permeability of the membrane 1.8-fold, while concomitantly increasing
the respiration rate of a typical produce commodity by 2.0-fold. The shelf life of the
produce is improved because the membrane permeability changes in response to
the fl uctuations in storage temperature and accommodates the changes occurring in
the respiratory requirements of the produce.
Table 14.3.
Permeabilities of ssc-coated membrane vs. polyethylene
ssc - Coated Membrane
Polyethylene (Low Density, 2 mm)
O
2
permeability
(cc/100 in
2
- atm - day)
280,000
254
CO
2
permeability
(cc/100 in
2
- atm - day)
1,120,000
1,102
Ethylene permeability
(cc/100 in
2
- atm - day)
1,080,000
508
H
2
O permeability to (g/m
2
- day)
849
16
