Control of Access of Microorganisms: Cleaning, Sanitation, and Disinfection ◾ 441
produce for washing and decontamination. 8,10,11 In addition, plant essential oils are also used at
various concentrations to disinfect produce surfaces. 12 Studies have shown that sequential washing
of alfalfa seeds, lettuce, and carrots with aqueous chlorine dioxide, ozone, and plant essential oils
allowed for a several-fold reduction in Esc. coli O157 counts in those products. 13,14
Applications of chemicals in gaseous form or in the vapor phase to decontaminate products
are drawing much attention because of their efficacy in improving shelf life and product safety.
Chemical sanitizers, such as chlorine, iodophors, or H 2 O 2, are widely used in liquid form to decontaminate equipment and have been discussed above. In this section, the application of chemicals
in gaseous or in vapor phase to decontaminate fruits and vegetables are discussed.
Chlorine
Chlorine is the most commonly used sanitizing agent, and it is used as sodium hypochlorite
(50–200 ppm) at a pH < 8.0 with a contact time of one to two minutes. A pathogen reduction
of 1–3 log CFU/g is commonly achieved with chlorine treatment. 15 In fresh-cut produce, components from tissue may neutralize chlorine action before it can exert its antimicrobial action on
microbes.
Chlorine dioxide gas (ClO 2 ) is a water-soluble neutral compound of chlorine, and it disinfects
by oxidation (see above). 8,16 It has 3.5 times more oxidative capacity than chlorine and is less reactive to organic compounds. The ClO 2 gas is unstable, and it is generated by reacting chlorine gas
(Cl 2 ) with sodium chlorite (2NaClO 2 ), thus generating 2ClO 2 gas and salt (2NaCl) when needed.
ClO 2 is permitted (Approval No. 21 CFR 173.300) up to 5 ppm in water for rinsing whole fresh
fruits and vegetables by the FDA in 1998. Application of ClO 2 gas for 10–30 minutes caused more
than a 5 log reduction of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on the
surface of various products, such as green peppers, strawberries, apples, and cantaloupes, while
maintaining the acceptable quality of the products. ClO 2 gas also reduced Salmonella by 4.50 log
in 10 minutes on almonds; 17 however, direct use of ClO 2 gas on these produce has not become
official yet.
Ozone
Ozone is a strong oxidizer and a colorless gas with a pungent odor and kills spoilage or pathogenic
microorganisms by oxidizing key cellular enzymes. 18 It has been used to treat drinking water to
kill pathogens. Ozone is unstable and decomposes quickly; thus, it has to be generated on-site
before use. Treatment of inoculated fruits and vegetables, such as black pepper, carrots, lettuce,
and blackberries, with ozone resulted in more than a 5 log reduction in Esc. coli O157:H7 counts
and 3–6 log reduction in Salmonella, Penicillium, and Aspergillus species. It has been also shown
that the shelf life of strawberries, raspberries, and grapes could be doubled with the application
of ozone at 2–3 ppm for a few hours per day. In recent years, ozone has been used to disinfect
produce rinse water for reuse in the produce industry as an environmentally friendly alternative
to chlorine.
Other gases or vapors, such as H 2 O 2 , allyl isothiocyanate gas, acetic acid vapor, and natural
plant volatiles, are shown to be effective in reducing the spoilage and pathogenic microorganisms
in varying degrees.
Application of ozone as a preservative has been approved. Acetic acid and H 2 O 2 are part of the
approved GRAS list; however, there is no regulation in the use of these and other plant oil–derived
gases/vapors on food products.
produce for washing and decontamination. 8,10,11 In addition, plant essential oils are also used at
various concentrations to disinfect produce surfaces. 12 Studies have shown that sequential washing
of alfalfa seeds, lettuce, and carrots with aqueous chlorine dioxide, ozone, and plant essential oils
allowed for a several-fold reduction in Esc. coli O157 counts in those products. 13,14
Applications of chemicals in gaseous form or in the vapor phase to decontaminate products
are drawing much attention because of their efficacy in improving shelf life and product safety.
Chemical sanitizers, such as chlorine, iodophors, or H 2 O 2, are widely used in liquid form to decontaminate equipment and have been discussed above. In this section, the application of chemicals
in gaseous or in vapor phase to decontaminate fruits and vegetables are discussed.
Chlorine
Chlorine is the most commonly used sanitizing agent, and it is used as sodium hypochlorite
(50–200 ppm) at a pH < 8.0 with a contact time of one to two minutes. A pathogen reduction
of 1–3 log CFU/g is commonly achieved with chlorine treatment. 15 In fresh-cut produce, components from tissue may neutralize chlorine action before it can exert its antimicrobial action on
microbes.
Chlorine dioxide gas (ClO 2 ) is a water-soluble neutral compound of chlorine, and it disinfects
by oxidation (see above). 8,16 It has 3.5 times more oxidative capacity than chlorine and is less reactive to organic compounds. The ClO 2 gas is unstable, and it is generated by reacting chlorine gas
(Cl 2 ) with sodium chlorite (2NaClO 2 ), thus generating 2ClO 2 gas and salt (2NaCl) when needed.
ClO 2 is permitted (Approval No. 21 CFR 173.300) up to 5 ppm in water for rinsing whole fresh
fruits and vegetables by the FDA in 1998. Application of ClO 2 gas for 10–30 minutes caused more
than a 5 log reduction of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on the
surface of various products, such as green peppers, strawberries, apples, and cantaloupes, while
maintaining the acceptable quality of the products. ClO 2 gas also reduced Salmonella by 4.50 log
in 10 minutes on almonds; 17 however, direct use of ClO 2 gas on these produce has not become
official yet.
Ozone
Ozone is a strong oxidizer and a colorless gas with a pungent odor and kills spoilage or pathogenic
microorganisms by oxidizing key cellular enzymes. 18 It has been used to treat drinking water to
kill pathogens. Ozone is unstable and decomposes quickly; thus, it has to be generated on-site
before use. Treatment of inoculated fruits and vegetables, such as black pepper, carrots, lettuce,
and blackberries, with ozone resulted in more than a 5 log reduction in Esc. coli O157:H7 counts
and 3–6 log reduction in Salmonella, Penicillium, and Aspergillus species. It has been also shown
that the shelf life of strawberries, raspberries, and grapes could be doubled with the application
of ozone at 2–3 ppm for a few hours per day. In recent years, ozone has been used to disinfect
produce rinse water for reuse in the produce industry as an environmentally friendly alternative
to chlorine.
Other gases or vapors, such as H 2 O 2 , allyl isothiocyanate gas, acetic acid vapor, and natural
plant volatiles, are shown to be effective in reducing the spoilage and pathogenic microorganisms
in varying degrees.
Application of ozone as a preservative has been approved. Acetic acid and H 2 O 2 are part of the
approved GRAS list; however, there is no regulation in the use of these and other plant oil–derived
gases/vapors on food products.