320 Produce Degradation: Reaction Pathways and their Prevention
Chlorine dioxide, ClO 2 , represents a valuable alternative to chlorine. It is also
often used as a disinfectant for fruits and vegetables. The advantages compared to
chlorine include lower reactivity with organic matter and insensitivity of the disin-
fection effect to pH. Chlorine dioxide is unstable and must be prepared on-site. It
can be explosive at higher concentrations. Its oxidizing power is about 2.5 higher
than that of chlorine. The mechanism of antimicrobial activity is similar to that of
chlorine in terms of disruption of cell protein synthesis and membrane permeability
control^ (Beuchat, 1998). Its use is also regulated. The FDA permits the use of ClO 2
for sanitizing equipment at a maximum of 200 mg/L. The maximum permitted
concentrations for the treatment of fruits and vegetables with intact cuticles and for
peeled products (e.g., potatoes) are 5 mg/L and 1 mg/L, respectively (Beuchat, 2000).
Peroxyacetic acid is a powerful oxidizing agent that decomposes on contact with
organic matter to form acetic acid. Peroxyacetic acid is the component of sanitation
preparations used for disinfection of surfaces in food production. Its disinfection
effect is comparable to that of chlorine (Winniczuk and Parish, 1997). The use of
peroxyacetic acid is also regulated, but it has been tested for sanitation of fresh-cut
fruit and vegetable surfaces by itself (Masson, 1990) and in combination with
octanoic acid (Hilgren and Salvedra, 2000).
Hydrogen peroxide is also one of the promising alternatives to chlorine. Accord-
ing to Sapers and Simmons (1998), treatment with H 2 O 2 was effective in reducing
the microbial contamination of whole cantaloupes, table grapes, prunes, raisins,
walnuts, and pistachios. Exposure to H 2 O 2 vapors caused bleaching of anthocyanins
in strawberries and raspberries, and dipping freshly cut green bell peppers, cucum-
bers, zucchinis, cantaloupes, and honeydew melons in a H 2 O 2 solution had no effect
on sensory quality but induced severe browning in shredded lettuce^ (Beuchat, 2000).
Residual H 2 O 2 might be eliminated by endogenous catalase, but in tissues with low
activity of catalase the residual peroxide can cause undesirable oxidation changes.
Application of organic acids as food additives was described as a method to
inhibit PPO activity. When organic acids are used for washing of fruits and vegetables
they should not be followed by rinsing with drinking water that will increase the
surface pH. The mode of action of organic acid is attributed to direct pH reduction
in microbial cells by dissociation of the undissociated acid molecule. Organic acids
can also disrupt the substrate transport by alteration of cell membrane permeability
and can inhibit NADH oxidation (Beuchat, 2000).^ Washing or dipping in solutions
of lemon juice, citric acid, acetic acid, or lactic acid, also in combination with other
disinfectants (chlorine), is used in early stages of fruit and vegetable processing.
Bromine has been used as a sanitizer in drinking water treatment, usually in
combination with chlorine. The combined use of chlorine and bromine results in a
synergistic effect^ (Beuchat, 1998).
Iodine compounds are often used as sanitizers for food processing equipment
and surfaces. Free elemental iodine and hypoiodous acid have microbicidal effects.
Iodine sanitation preparations are ethanol iodine solution, aqueous iodine solutions,
or iodophors (combination of elemental iodine and nonionic surfactants with a
polymeric carrier).
Trisodium phosphate (alkali) disinfectant, such as is used to reduce Salmonella
in poultry and red meat, has been tested for reduction of Salmonella on the surface