318 Produce Degradation: Reaction Pathways and their Prevention
cells that can facilitate microbial growth. To reduce microbial contamination, wash
water must not be contaminated and should be able to rinse out the superficial
impurities from the products. Washing in flowing water or air-bubbling water is
preferable to dipping into still water (Ohta and Sugarawa, 1987). The temperature
of wash water should be as low as possible, preferably below 5°C. The required
amount of wash water depends on the type of produce and on the extent of pollution
and varies between 5 and 10 L/kg of produce. In the case of washing after peeling
it is about 3 L/kg (Laurila and Ahvenainen, 2002). Wash water should be removed
from the produce. A centrifuge is usually used, but the conditions of centrifugation
(time and rate) should be optimized according to the produce to remove free water
without damaging cells.^ Recently, gentle drying with cheescloth has been proposed
(Zomorodi, 1990; Bolin and Huxsoll, 1991; Gorny et al., 2002).
10.2.3.1.2 Disinfection and Decontamination
The effectiveness of washing can be increased by addition of disinfectants or preser-
vatives to the wash water. The use of sanitizers at concentrations higher than usual
residual levels of chlorine or other disinfectants permitted for drinking water treatment
is regulated. A list of the U.S. regulations dealing with disinfection of raw fruits and
vegetables is given by Beuchat (2000). Generally, it is possible to use any sanitizers
that are used for disinfection of food products. The use of some of these is, however,
limited or regulated in some countries for fruit and vegetable handling and processing.
Chlorine is widely used for the disinfection of drinking water. It is also used for
the disinfection of whole and cut fruits and vegetables as well as the surfaces that are
in contact with produce during handling. Chlorine is commonly used at 200 mg/kg
(available chlorine) and at pH below 8 (usually at 6.0 to 7.5 for effective disinfection
without damaging equipment surfaces), with contact times ranging from 1 to 2 min. It
is applied in the form of liquid chlorine (Cl 2 ), sodium hypochlorite, or calcium hypochlo-
rite. When these substances are added to water, they undergo the following reaction:
Cl 2 + H 2 O → HOCl + H+ + Cl–-NaOCl + H 2 O → NaOH + HOClCa(OCl 2 ) + 2 H 2 O → Ca(OH) 2 + 2 HOClHOCl → H+ + OCl–Microbicidal activity is controlled by the amount of free available chlorine (as
hypochlorous acid, HOCl) in the water that comes in contact with cells (Beuchat,
1998).^ The dissociation of HOCl depends on pH (Table 10.8).
The antimicrobial action of chlorine is based on its powerful oxidizing effect
and rapid linkage of proteins, including the cell membrane proteins. N-chloro com-
pounds are formed and interfere with glucose oxidation or oxidation of sulfhydryl
groups. Chlorine impairs membrane permeability and transport of extracellular nutri-
ents (Camper and McFecters, 1979; Beuchat, 2000).^ Chlorinated water is widely
used for the disinfection of whole fruits and vegetables as well as freshly peeled,