172 Produce Degradation: Reaction Pathways and their Prevention
The characteristics of these products differ considerably from their intact coun-
terparts. The act of cutting or shredding the tissues results in a large cut surface area
of damaged cells, leading to greater instability and much shortened shelf life of only
a few days, since cut or damaged produce has a respiration rate higher than that of
undamaged tissue [191]. In addition, physical injury such as wounding or bruising
can stimulate ethylene production [172].
Flavor and appearance have been observed to deteriorate faster in various cut
vegetables (lettuce, carrot, celery, endive, and radish) than in undamaged tissues
[191]. Discoloration, off-flavors, and drying of product are the main determinants
of shelf life [192]. In terms of flavor, both aroma and taste components may be
affected. Decreases in sucrose, glucose, fructose, and malic acid were observed for
grated carrot during storage at 2°C [193]. Lamikanra and Richard [194] observed a
decline in esters and in β-ionone and geranylacetone during storage of fresh-cut
cantaloupe. Factors affecting flavor and shelf life of fresh-cut fruits and vegetables
have been reviewed recently [195].
6.4.4 AROMA MODIFICATION BY EXOGENOUS VOLATILES
In addition to the well-known ethylene modulating compounds 1-methylcycloproene
and methyl jasmonate [196], various other volatile compounds have been shown to
affect the production of volatiles of whole and fresh-cut fruits during storage.
Treatment or CA exposure of strawberries with acetaldehyde vapor can suppress
mold development and improve color [197]. However, acetaldehyde treatment can
alter the volatile profiles of strawberries and other fruits. Acetaldehyde treatment of
feijoa fruit was shown to increase ethyl butanoate concentrations during storage [198].
The nature and extent of the volatile profile change depends on the acetaldehyde level
used, the duration of treatment, and the biochemical pathways involved [199].
6.4.5 COATINGS AND WRAPS
Coating the surface of fruits and vegetables with waxes or other suitable material can
have beneficial effects in terms of improved moisture retention and reduction of CO 2
and O 2 exchange. The effect may be positive or negative in terms of flavor, since reduced
respiration is often desirable, but a coating that is too thick may reduce respiration to
the point where fermentation is favored, leading to off-flavors. Initial studies indicated
that citrus fruits did not respond well to waxing [200], but more recent investigations
with shellac coatings indicated some advantages of coating in regard to moisture reten-
tion and appearance, with minimal effects on volatile composition [201]. Application
of high-density polyethylene film (wrap) is a good alternative to waxes since it provides
good water vapor barrier properties while not affecting the movement of respiratory
gases and contributing to the development of off-odors [202].
6.4.6 CURING
Under proper storage conditions (curing) some root and tuber crops, such as sweet
potatoes and Irish potatoes, have the ability to heal minor wounds incurred during
harvest and handling.