294 Produce Degradation: Reaction Pathways and their Prevention
10.1 MECHANISMS OF SPOILAGE OF FRESH AND
PROCESSED PRODUCEFresh fruits and vegetables and other products of plant origin are available fresh
only during a brief harvest period. It is necessary to keep supplies of harvested food
edible over relatively long periods of time. Empirical preservation methods have
been used since ancient times; more recently, increasingly sophisticated preservation
methods have been developed (Lück and Jager, 1997).This chapter is not an exhaus-
tive review of changes that occur in produce and preservative methods to minimize
them, but a brief summary that serves as an introduction to the methods of food
preservation. Generally, produce degradation begins after harvest and continues
during processing and storage until the product is consumed or becomes inedible
or unsafe for consumption. These changes could be generally classified to four
groups: physiological, enzymatic, chemical, and microbial changes.
10.1.1 PHYSIOLOGICAL CHANGES
Physiological changes are more complex and proceed in the organelles, cells, or tissues.
An increase in the rate of these changes is caused by conditions that accelerate the rate
of natural deterioration, such as high temperature, low atmospheric humidity, and
physical injury. Abnormal physiological deterioration occurs when fresh produce is
subjected to extremes of temperature, atmospheric modification, or contamination. This
may cause unpalatable flavors, failure to ripen, or other changes in the living processes
of the produce, making it unfit for use (Barbosa-Cánovas et al., 2003).
10.1.1.1 Mechanical Damage
Careless handling of fresh produce causes internal bruising, which results in phys-
iological damage or splitting and skin breaks. This increases the rate of water loss
and the rate of normal physiological breakdown. Skin breaks also provide sites for
infection by disease organisms causing decay. The injuries can result in tissue
browning, higher respiration and ethylene production rates, and some undesirable
compositional changes, such as loss of ascorbic acid content and development of
off-flavors. Mechanical damage can also activate the protection mechanisms of the
tissues. An increase in polyphenoloxidase (PPO) activity, possibly from production of
new PPO from the latent form of the enzyme, and production of quinones in the first
stage of enzymatic browning reactions are examples of plant injury-induced defense
responses. Similarly the biosynthesis of the steroidal glycoalcaloids saponine and cha-
conin occur during the storage of peeled, cut potato tubers (Glynn and Dixon, 1996;
Dale et al., 1998). The highest levels of furanocoumarins were found in mechanically
damaged and/or rotten impaired samples of parsnip and celeriac (Schulzova et al., 2002).
10.1.1.2 Temperature Injuries (Chilling, Freezing, and
High-Temperature Injury)Certain injuries can occur during storage under suboptimal conditions. Chilling
injury usually occurs to commodities of tropical origin at temperatures below 10 to