Controlled and Modified Atmosphere Storage - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 155

shelf life of only 4 weeks under optimal conditions of 0°C and 100% relative
humidity. 52 Storage life of this produce, however, can be extended with the use of
CA. Romo-Parada et al. 53 reported that under a CA of 3% O 2 and 2.5 to 5% CO 2
cauliflower was still commercially acceptable after 52 days of storage. Storage under
higher CO 2 levels, however, causes yellowing, softening, and microbial breakdown
Lettuce is also a short storage crop, and when its temperature is reduced rapidly to
0°C and held at this level while the humidity is kept very high, head lettuce can be
stored for 2 to 3 weeks. 1 Under CA of 2.5% CO 2 and 2.5% O 2 at 2°C head lettuce
can be stored for up to 75 days. 54 Studies of CA storage of minimally processed
lettuce have shown that CA (3% O 2 , 10% CO 2 ) can prolong the shelf life of shredded
iceberg lettuce by limiting plant and microbial enzyme activity, without appreciably
affecting microbial development. 55
CONTROLLED ATMOSPHERE STORAGE OF CEREALS
AND OILSEEDS
P RINCIPLE
In CA storage, an environment that is lethal to stored-grain pests is created by
changing the proportions of CO 2 , O 2 , and N 2 in the atmosphere surrounding the bulk
grain in storage structures. Controlled atmosphere storage is different from an air-
tight storage where gas ratios change naturally, although both are carried out in more
or less gas-tight storage structures. In air-tight storage, the depletion of O 2 and the
accumulation of CO 2 occur due to the metabolic processes of the insects, microflora,
and the stored grain. Because the effectiveness of the air-tight storage is largely
dependent upon the build-up of an infestation in the grain, it is not considered a
satisfactory method. Controlled atmospheres are attained by introducing CO 2 or N 2
from external sources, possibly prior to the build-up of infestation, thereby prevent-
ing damage to the stored grain. Air-tight storage and CA storage are collectively
referred to as modified atmospheres (MA) and typical compositions of various
controlled atmospheres in stored grain are given in Table 5.8 . 56
A DVANTAGES AND L IMITATIONS
The main advantage of CA to disinfest grain is its potential to replace pesticides
used in the grain industry. The CA-treated grain does not have any chemical residues
which can cause considerable health concerns. In addition to providing an effective
control of pests, CA storage prevents mold growth, preserves grain quality, and
maintains a high level of germination in the stored grain. 57 However, as with any
other method of pest control, CA storage has limitations. The major limitation
appears to be the high initial cost of air-tight storage structures, and the cost of
sealing existing structures to the desired air-tightness. 58,59 There is also the cost of
the generation and transportation of the gas. The interaction of CA gases with the
storage structure can cause some practical problems. The introduction of CO 2 or N 2
into airtight structures has the potential to increase the internal pressure on bin walls,
and steps need to be taken to permit pressure equilibration. The only chemical