Mechanisms of Microbial Spoilage of Fruits and Vegetables 471
will be cited repeatedly later in this chapter, as part of the case studies of key fruits
and vegetables. Stored produce that is clean from the field may still become infected
by contact with contaminated surfaces (equipment, hands, detritus, etc.), and via
infiltration or absorption of contaminated wash water. Wounds provide common
entry points, and the bacteria multiply in intercellular spaces. Produce that is under
attack by soft-rotting bacteria can quickly degrade, such that by the time a soft-rot
infection is apparent by appearance or by a characteristic smell the shelf life of the
produce can be counted in days, if not hours. In the initial phase of infection by
Erwinia, the bacteria reproduces on the surface and internally without digesting the
polysaccharide matrix of the cell wall; when the population density reaches a critical
level, a quorum-sensing pathway is initiated. Acyl-homoserine lactone (AHL) is a
signal molecule that initiates the production of pectolytic enzymes that release oligo-
and monosaccharides on which the bacteria feed, degrading the plant tissues in the
FIGURE 15.4Various methods of penetration of plant tissue by phytopathogenic fungi (top
three rows) and bacteria (bottom row). (From Agrios, 1997. With permission.)