Flavor and Volatile Metabolism in Produce 173
Curing with respect to bulb crops, such as onions and garlic, is much different
from what is used for root and tuber crops. In this case curing is a dehydration
process that readies the produce for prolonged storage. The effect of curing on flavor
of bulb crops is uncertain; however, curing is known to affect the flavor potential
of some tuber crops, such as sweet potatoes [203]. In this case, curing of sweet
potatoes increases the levels of amylotyic enzymes that are responsible for starch
degradation to maltose during baking, leading to a sweeter flavor as well as increased
levels of thermally derived (via Maillard reaction) aroma components [204].
6.4.7 IRRADIATION
For more than 30 years there have been many studies on the application of irradiation
for improving the keeping quality of produce. Low-dose gamma irradiation delays
ripening by reducing respiration in some fruits and vegetables, and irradiated produce
remains edible for longer periods because senescence is delayed [205]. In addition,
low-dose irradiation functions as an effective quarantine method against fruit flies
and other insects, and fungal development and microbial spoilage may also be
delayed. In tuber crops, such as potatoes, onions, carrots, etc., low-dose irradiation
is an effective means of suppressing sprouting and controlling fungal and bacterial
pathogens, which prolongs shelf life. In general, when doses are kept within rec-
ommended allowances, application of low-dose irradiation is an effective means for
shelf-life extension in fruits and vegetables without significant deleterious changes
in flavor [206,207].
6.4.8 OFF-FLAVOR AND TAINTS
Off-odors can be formed in fresh produce by microbial and chemical transformations
during harvesting, processing, packaging, and storage. They also may be introduced
(taints) by absorption of alien chemicals from water used in processing, from pack-
aging materials, and from the environment in which the produce has been grown,
processed, and stored [208].
Understanding the physiology of fresh produce is fundamental to understanding
its stability and likely shelf life. Factors that affect stability and shelf life and quality
attributes such as appearance, texture, and flavor of fruits and vegetables have been
reviewed.
6.4.8.1 Anaerobiosis and Off-flavor Development
Off-odors can result if fruit or vegetable tissues undergo anaerobic respiration
(fermentation or anaerobiosis) [209], leading to formation of lactic acid, acetic acid,
ethanol, and other volatiles [210,211]. Furthermore, CO 2 in aqueous solution is a
strong oxidant that causes bleaching of color and generation of off-odors.
Storage of fruits under an anaerobic environment (anoxia) has been shown to
result in off-flavor development [212]. Anaerobic respiration leads to accumulation
of acetaldehyde and ethanol, which increases with time of exposure in static N 2
(or decreased O 2 ). In commodities such as apples the anaerobic profile included high
concentrations of ethanol [213]. In addition, anoxic conditions that favor ethanol