174 Produce Degradation: Reaction Pathways and their Prevention
production were reported to inhibit the formation of ethanol-derived esters in Red-
chief Delicious apples [214]. The effects may be at least partially reversible due to
possible conversion of alcohols to esters or other modifications via oxidation upon
return of the fruit to air [166,212,214]. Anaerobic pretreatment may have a positive
influence on flavor in some instances. It has been shown to increase aroma-relevant
volatiles in some fruit, such as citrus [215], and was shown to increase levels of
ethyl butanoate and ethyl acetate in feijoa [198].
Some fresh produce is more susceptible to the development of off-odors than other
commodities. For example, strong off-odors have been reported for broccoli stored in
O 2 levels less than 0.5% [216–219]. Forney et al. [217] monitored the formation of
volatiles by broccoli stored under CA conditions (0.5% O 2 ) and found ethanol, acetal-
dehyde, methanethiol, hydrogen sulfide, octane, methyl acetate, ethyl acetate, and di-
methyl sulfide. Methanethiol was considered to be primarily responsible for the off-
odor. Likewise, scallions during storage at 0 to 5°C developed propanethiol S-oxide
[220].
6.4.8.2 Ethylene-Induced Off-Flavors
Ethylene is produced in copious amounts to mediate the defense response of stressed,
diseased, and injured tissues. Parsnip roots exposed to ethylene developed higher
levels of total phenolics and bitterness (after cooking) compared with controls [221].
Similarly, exposure of mature carrots to ethylene resulted in higher content of bitter
isocoumerin in the peel [222]. Injured carrots (sliced, cut, or bruised) exposed to
ethylene showed greater rates of isocoumarin accumulation than intact (uninjured)
specimens. This enhanced ethylene sensitivity has been observed in mechanically
wounded lettuce [223] and has major implications in relation to prepared salads and
other fresh-cut produce.
6.4.8.3 Sanitizers and Chemical Treatments
Prior to grading, processing, and packaging, produce is often washed with chlori-
nated (50 to 100 ppm) or ozonated water [224] to help control fungal and bacterial
pathogens, but this practice may lead to off-odors [225]. For example, chlorine
disinfection is known to cause formation of compounds with musty and medicinal
off-odors, such as trichloroanisoles [208]. Fungicides and sprouting inhibitors are
approved for use on some produce [226] and provide another potential source of
off-odors. For example, potatoes treated with isopropyl-N-(3-chlorophenyl)carba-
mate and HiSol carrier (mixture of aromatic hydrocarbons) were found to impart
an off-odor caused by high levels of benzene derivatives, some of which were
components of the HiSol carrier [227].
It should be noted, however, that musty/earthy aromas are not always negative,
but can be associated with the characteristic and desirable flavor of some produce,
such as beets, in which geosmin is responsible for the characteristic aroma in both
raw and cooked beets [228]. Geosmin also has been reported as a normal volatile
component of sweet corn [229]. Earthy smelling 2-methoxy-3-isopropylpyrazine is
important in the aromas of raw potatoes [230], raw peas [231], and other raw
vegetables [144].