Agriculture Reference
In-Depth Information
membrane of the cell wall (Aieta and Berg 1986). The effi cacy of chlorine dioxide
varies based on concentration, exposure time, and temperature, and to some extent
based on pH, type of fruit or vegetable, and microbial species (Zoffoli and others
2005; Zhang and Farber 1996; Benarde and others 1965). Roberts and Reymond
(1994) evaluated the use of chlorine dioxide in a commercial apple presize dump tank
and concluded that 3-5 ppm of chlorine dioxide effectively controlled fungal spores
in the recirculated process water. Reina and others (1995) concluded that 1.33 ppm
chlorine dioxide effectively controlled the microbial buildup in the hydro-cooling
water of cucumbers, but had little effect on the microorganisms on the fruit. Other
studies have shown that exposure to 10 ppm of chlorine dioxide for 20 min was
required to inactivate Monilinia laxa on infected wounds on nectarines (Mari and
others 1999), and only 30 sec was necessary to control fungal pathogens associated
with pears (Spotts and Peters 1980). Zhang and Farber (1996) found that a 10-min
exposure of shredded lettuce or cabbage to 5 ppm chlorine dioxide caused a 1.1-log
reduction of L. monocytogenes , while Rodgers and others (2004) achieved a 4-log
reduction using 5 ppm for 5 min against L. monocytogenes on shredded lettuce. The
difference in results from these studies is likely due to variations in the methods
employed. More substantial reductions of pathogens on the surface of produce have
been achieved by treatments with gaseous chlorine dioxide (Sy and others 2005; Sun-
Young and others 2004; Du and others 2003; Han and others 2000).
Acidifi ed Sodium Chlorite
Acidifi ed sodium chlorite (ASC) forms by combining a weak acid such as citric acid
with sodium chlorite in aqueous solution. It is done under strictly controlled conditions
of concentration and pH to minimize the production of chlorine dioxide and maximize
the formation of chlorous acid (HClO 2 ). It is characterized by the following
reaction:
(
)
Weak Acid H
+
+
NaClO
HClO
It is hypothesized that the uncharged chlorous acid is able to penetrate bacterial
cell walls and disrupt protein synthesis by virtue of its reaction with sulfhydryl, sulfi de,
and disulfi de containing amino acids and nucleotides. The undissociated acid is
hypothesized to facilitate proton leakage into cells and thereby increase the energy
output of the cells to maintain their usual internal pH. Disruption of membrane activity
adversely affects amino acid transport (Warf and Kemp 2001).
Acidifi ed sodium chlorite is approved for washing fruits and vegetables at levels
that result in chlorite concentration of 500 ppm and 1200 ppm in combination with
any generally recognized as safe (GRAS) acid at levels suffi cient to achieve a pH
between 2.3-2.9 and must be followed by a potable water rinse or by blanching,
cooking, or canning (Anonymous 2007c). In literature reports, ASC has shown prom-
ising results on pathogen populations inoculated onto produce surfaces and appears
to be more tolerant to organic loading. However, some published studies have reported
organoleptic effects to certain produce when using high levels on cut surfaces.
The treatment of Chinese cabbage with 500 ppm ASC at pH 2.2-3.1 using various
organic acids and a treatment time of 15 min signifi cantly reduced levels of E. coli
O157:H7 by 2.5 - 3.0 log CFU/g without causing apparent changes in color (Inatsu and
2
2
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