Mechanisms of Microbial Spoilage of Fruits and Vegetables 469
15.3.2 PATHOGEN ATTACK
The second element in the progression of microbial spoilage is the introduction of
a compatible pathogen to the produce. Bacterial and fungal phytopathogens can be
introduced to fruits and vegetables at almost any point during the growth, maturation,
harvest, storage, or shipment of the produce by exposure to contaminated water,
dust, mechanical equipment, etc. (Beuchat, 1995). As previously indicated, the
surfaces of fruits and vegetables have evolved to present as impervious a barrier as
feasible, with multiple layers of chemical and mechanical defenses. Thus, while the
first step in spoilage is getting the pathogen onto the produce, the second, more
important step in spoilage is getting the pathogen into the produce. Obligate phyto-
pathogens have evolved a suite of tools that allows them to penetrate the plants’
defenses. These may take the form of specialized physical structures, such as fungal
appressoria (Figure 15.4), in addition to specialized enzymes that can degrade the
FIGURE 15.2Cross-sectional anatomy of leaf tissue. (From Mauseth, 1988. With permission.)