Produce Degradation Pathways and Prevention

306 Produce Degradation: Reaction Pathways and their Prevention

MAS are made airtight and the concentration of oxygen, carbon dioxide, and ethylene
is monitored and regulated. The optimal compositions of gases are close to those
described for MAP below and differ according to the type of fruits or vegetables, and
also according to cultivar. Examples of atmospheres for CAS are given in Table 10.5.
Another way to reduce the oxygen content in the surrounding atmosphere is
through pressure reduction. Hypobaric storage, patented by Burg in the late 1960s,
is still used with various modifications. One of the systems is called moderate
vacuum packaging (MVP). In this system, fresh produce is packed in a rigid, airtight
container under 40 kPa of atmospheric pressure and stored at refrigerated tempera-
ture (4 to 7°C). The effect of hypobaric storage on the physiological changes of
fresh produce is similar to the effect of MAP. Experiments have been conducted
that confirm beneficial effects against spoilage and pathogenic microflora (Day,
1990). When gas flushing is used with MAP, the composition of the gas mixture is
usually 3 to 10% CO 2 , 2 to 10% O 2 , and 80 to 95% N 2. The aim is always to create
optimal gas equilibrium to reduce respiration to a minimal level, but the concentra-
tions of carbon dioxide and oxygen must not be detrimental to the produce. The
equilibrium concentrations are 2 to 5% CO 2 and 2 to 5% O 2 and the rest is nitrogen
(Kader et al., 1989; Powrie and Skura, 1991). It is usually difficult to achieve these
conditions in ready-to-eat or ready-to-use fresh fruit or vegetable products with
extended shelf life. The main problem is the lack of packaging materials that are
permeable enough to match the respiration of fresh produce (Day, 1994). The most
permeable packaging films, such as polyethylene and oriented polypropylene are
not permeable enough to allow longer shelf life of packed produce, especially when
the produce has high respiration. Respiration can be reduced storing produce at a
low temperature. One of the solutions used is to make microholes of defined sizes
and defined quantity in the packaging material to avoid anaerobic respiration (Ketel-
eer and Tobback, 1994). The search for plastic films of higher permeability continues.
New materials being proposed include laminated films with ethylene vinyl acetate,
oriented polypropylene and low-density polyethylene, combinations of ceramic
materials with polyethylene, or the incorporation of finely dispersed minerals in the
packaging film. These new films posses higher permeability than polyethylene or

TABLE 10.5

Examples of Refrigerated (3.5°C) Storage

Atmospheres Composition of CAS

Product

O 2

(%)

CO 2

(%)

N 2

(%)

Shelf life

(months)

Apples, Bramley ́s seedling 13 8 79 5

Apples, Cox ́s Orange Pippin 3 5 92 5

Apples, Cox ́s Orange Pippin 1 1 98 8

Winter white cabbage 3 5 92 10

Source:Adapted from Fellows, P., Food Processing Technology: Prin-

ciple and Practice, 2nd ed., CRC Press, Boca Raton, FL, 2000c, Part 4.