Agriculture Reference
In-Depth Information
pH
Beside concentration, the pH of a solution can impact the bactericidal effect of certain
antimicrobials. An increase in pH substantially decreases the biocidal activity of
chlorine; a low pH environment favors the formation of hypochlorous acid (HClO),
which increases the bactericidal activity of the wash solution. The same is true for
acid sanitizers. The pH of the solution must be at or below the dissociation constant
(or pKa) of the acid in order for it to be effective. Other chemical oxidants can be
infl uenced by pH, but not to the same extent as chlorine or acids.
Sanitizer Flow Hydrodynamics
Generally, high shear rates on produce surfaces during a wash operation increase
detachment of attached bacteria (Chang and others 1991). Mechanical forces due to
liquid fl ow enhance the removal of attached bacteria from tissues and food contact
surfaces. In addition to shear forces generated by liquid fl ow and turbulence, other
physical methods, such as pressurized water jet and ultrasonic treatment, have also
been used to increase the shear rate on produce surfaces (De Zuniga and others 1991).
Increasing the turbulence of the wash water is important to ensure adequate contact
to produce surfaces and removal of debris and microorganisms. Longley (1978) pro-
posed that bacterial cells form protective clusters during exposure to a sanitizer.
Increased turbulence in a washing operation may aid in enhancing the activity of the
antimicrobial by breaking up the clusters and increasing the accessibility of the anti-
microbial to individual bacterial cells (Wang 2006). Water jets, air bubbling or injec-
tion, and gravity fl ow have all been used by the produce industry as mechanical means
to increase turbulence in a wash process.
Water Quality
Organic Loading
Because most of the antimicrobial agents used in washing fruits and vegetables are
also oxidizing agents, they often react chemically with organic materials, which causes
the depletion of the effective component of the antimicrobial in the wash water (Table
9.1). The organic materials encountered in produce washing may include fruit and
vegetable tissue, cellular fl uids exuded by cutting, soil particles, insects, and microbes.
Because wash water is generally reused, the accumulation of organic matter in the
wash water causes a decrease in the effective concentration of the antimicrobial, and
thereby contributes to an increased risk of contamination of foodborne pathogens. It
is therefore important to understand the effect of organic loading on the antimicrobial
Table 9.1.
Oxidation capacity of antimicrobials
Oxidizing Agent
Electron Volts (eV)
Ozone
2.07
Peracetic acid
1.81
Hydrogen Peroxide
1.78
Chlorous acid (ASC)
1.58
Chlorine dioxide
1.57
Sodium hypochlorite
1.36
