Flavor and Volatile Metabolism in Produce 171
are used to control movement of respiratory gases. Depending on the film, lowered
O 2 and raised CO 2 levels within the package can lead to a reduction in respiration
of the produce and potentially longer shelf life. One potential drawback to MAP is
the potential for O 2 levels to fall too low and cause production of off-odors due to
fermentation.
Although respiration rate is important, its reduction is not the only beneficial
effect of altered atmospheres. Increased CO 2 levels also influence (suppress) ethylene
production and thus affect ripening and flavor development [172,177]. Volatile pro-
duction tends to peak within a few days during the beginning of storage, in associ-
ation with ripening, and then tends to drop rapidly as substrates are depleted and
senescence sets in. CA-stored produce generally exhibit a slow rate of aroma pro-
duction over a prolonged period, except under low O 2 levels, in which case anaer-
obiosis occurs, leading to formation of ethanol and other volatiles. Brackman et al.
[178] reported that apple cultivars whose aroma precursors are derived principally
from fatty acid metabolism (ester cultivars) were more susceptible to aroma sup-
pression under CA than apples that biosynthesize aroma primarily from amino acids
(alcohol-type cultivars). Yahia et al. [179] reported that loss of volatiles from apples
stored under CA can be considerable and the severity is dependent on the atmosphere
composition and duration of storage. For example, low-ethylene CA storage sup-
pressed production of butanoate, 2-methylbutanoate, pentanoate, and hexanoate
esters, while acetate esters were unaffected [179]. CA storage can reduce aroma
production when apples are ripened after storage with varying effects on the different
aroma constituents [66,180]. CA storage under high CO 2 and low O 2 suppressed
synthesis of branched-chain aroma components [181]. In apples, the generation of
esters, which takes place mainly in the peel of intact fruit, is oxygen-dependent [182].
Alternatives to the usual high-CO 2 , low-O 2 CA and MAP practices have been
developed in recent years. Use of novel noble gas mixtures in MAP (e.g., argon, 70 to
90%; CO2, 0 to 20%; O 2 , 0 to 15%) was shown to improve quality and lengthen
shelf life of prepared salads [183]. On the other hand, strawberries stored in MAP
with argon containing high CO 2 and high O 2 levels experienced altered ester syn-
thesis [184].
CA and MA are not necessary for some vegetables such as potatoes, carrots,
garlic, and onions. On the other hand, use of CA and MA has been found to benefit
broccoli, cabbage, lettuce, asparagus, and brussels sprouts [185].
6.4.3.1 MAP of Fresh-Cut Fruits and Vegetables
One area where MAP has been utilized is for fresh-cut or minimally processed
produce, such as salads and fruit pieces, to prevent rapid deterioration that occurs
once fresh produce has been cut [186,187]. Prepared or fresh-cut fruits and vegeta-
bles represent a group of short-shelf-life produce that has experienced considerable
growth in the past decade [188,189]. Examples range from ready-to-eat washed,
sliced, chopped, or shredded prepared fruits or vegetables, such as salads and cole-
slaw mixes, to diced, cubed, or segmented fruit and stir-fry products. The biochem-
istry, physiology, microbiology, and quality factors in fresh-cut fruit were the subject
of a recent book [190].