Biomedical Engineering Reference
In-Depth Information
This chapter provides an overview of the benefits and concerns of CA and MA
storage, the methods for creating and maintaining MA conditions, and the effects
of CA and MA on shelf life extension and quality of food products, especially fruits,
vegetables, grains, and oilseeds.
CONTROLLED AND MODIFIED ATMOSPHERES
FOR FRUITS AND VEGETABLES
P
RINCIPLE
The principle behind controlled and modified atmosphere technologies is to reduce
the rate of respiration, reduce microbial growth, and retard enzymatic spoilage by
changing the gaseous environment surrounding the food product. This is achieved
by reducing the concentration of oxygen (O
2
), which is required in respiration, or
by adding an inhibitory gas such as carbon dioxide (CO
2
) or carbon monoxide (CO).
The balance between O
2
and CO
2
is critical, and an optimal ratio is required for
each specific product. A major difference between CA and MA storage is in the
degree of control of the gaseous composition of the storage atmosphere. The CA
implies a higher degree of control than MA in maintaining specific levels of O
2
,
CO
2
, and other gases. Also, in MA storage the composition of the atmosphere
surrounding the product is generally created and maintained by the interaction of
the commodity's respiration with the permeation of respiratory gases through the
packaging material.
2,8,9
Modified atmosphere conditions can also be established and
adjusted by pulling a slight vacuum and replacing the package atmosphere with a
desirable gas mixture, which can be further adjusted through the use of O
2
, CO
2
, or
ethene (C
2
H
4
) absorbers.
2,9
In CA storage facilities, both temperature and gas composition of the storage
atmosphere are regulated or controlled. The gas concentration ranges encountered
in CA storages are 1 to 10% O
2
, 0 to 30% CO
2
, and the balance is nitrogen (N
2
).
10-12
Air consists of approximately 78% N
2
, 21% O
2
, 0.03% CO
2
, and traces of several
other gases that have no physiological significance.
B
ENEFITS AND
C
ONCERNS OF
CA
AND
MA S
TORAGE
The benefits and concerns of CA and MA storage have recently been reviewed by
several authors.
2,5-8,13-16
The benefits can be divided into quality advantages and
marketing and distribution advantages. The improvements in quality arise from the
general reduction in the rates of metabolic processes, retardation of physiological
aging, enzymatic spoilage, and reduction in microbial growth. In fresh fruits and
vegetables stored under optimal CA or MA, practical quality advantages include:
1.
Reduction in chlorophyll breakdown, with a resulting higher color stability.
2.
Reduction in enzymatic browning in cut produce, whenever low levels of
O
2
are used.
3.
Improvement in texture caused by the action of CO
2
on enzymes acting
on cellular membranes.
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