454 Produce Degradation: Reaction Pathways and their Prevention
bacterial infiltration during washing. Fruits with cuts, bruises, or punctures are
relatively more susceptible to bacterial infiltration (Buchanan et al., 1999; Merker
et al., 1999). Flume and wash waters have been reported to be possible contributors
to bacterial contamination in fresh produce (Bartz and Showalter, 1981; Bartz, 1999;
Buchanan et al., 1999; Merker et al., 1999; Walderhaug et al., 1999; Burnett et al.,
2000).
Control of wash water temperature and the depth at which fresh produce is
immersed is an additional intervention to prevent bacterial infiltration. Bartz (1982)
recommended that the water used in handling or washing fresh produce should be
warmer than the incoming fruits and vegetables except for the following conditions:
(1) the fruit or vegetable is not susceptible to infiltration (2) the fruit or vegetable
and the wash water are not contaminated with undesirable microorganisms or sub-
stances; and/or (3) the shelf-life and quality if the fruit or vegetable would not be
substantially affected by infiltration. As fruits and vegetables are immersed to greater
depths in water the increase in hydrostatic pressure on their surfaces can facilitate
bacterial infiltration (Bartz, 1982, 1999). When tomatoes were subjected to pressure
to simulate an immersion depth of 24 inches in water, the incidence of microbial
spoilage increased from 20 to 40% following exposure times of 2 and 10 min,
respectively. When the pressure on tomatoes was increased to simulate a depth of
48 inches, exposure for only 1 sec caused a 70% incidence of spoilage (Bartz, 1982).
Based on these findings, overloading of dump tanks and prolonged immersion of
produce in water should be avoided to prevent bacterial infiltration.
The fact that infiltration can occur rapidly under relatively high hydrostatic
pressure justifies the need for adequate concentrations of sanitizer to inactivate
bacteria immediately when produce is immersed in the dump tank. Also, adequate
amounts of sanitizer are necessary to prevent cross-contamination. Research findings
indicate that if chlorination of water used for washing apples is inadequate to prevent
cross-contamination, then uncontaminated apples are likely to be infiltrated by
E. coli O157:H7 (Buchanan et al., 1999). Dipping surface-inoculated tomatoes in
water with a free chlorine concentration of 60 to 110 ppm significantly (P < 0.05)
reduced populations of Salmonella Montevideo; however, increased concentrations
of up to 320 ppm did not produce a significant reduction compared to dipping in
water with 110 ppm free chlorine (Zhuang et al., 1995) The incidence of postharvest
disease linked to infiltration of tomatoes with contaminated water was decreased but
not eliminated by 50 to 100 ppm free chlorine in wash water (Bartz, 1988). These
results indicate that treatment of fresh produce with chlorine may not be fully
effective in destroying various types of microorganisms that could be present on
tomatoes in the packing house (Senter et al., 1985). Zhuang et al. (1995) recom-
mended that tomato packing houses maintain their dip tanks at a higher temperature
than that of the tomatoes and at a free chlorine concentration of 200 ppm. As with
any other sanitizer, careful monitoring of the concentration of chlorine, in the form
of hypochlorous acid, is necessary to maintain adequate levels of the sanitizer for
destroying microorganisms in produce wash water. Maintaining adequate levels of
hypochlorous acid to effect microbial destruction in wash water could be difficult
since chlorine readily reacts with organic matter. In this regard, debris of harvested
produce and exudate from damaged tissue of fresh produce may neutralize some of