Mechanisms of Food Additives, Treatments, and Preservation Technology 319
cut, or shredded produce. Lowering pH, increasing temperature, or adding surfac-
tants can increase the efficiency of treatment. Toxic chlorine gas is liberated from
solutions of hypochlorite at pH below 4.0. The use of warm wash water is not usually
applicable for raw fruits and vegetables. This accelerates microbial growth and
increases the risk of infiltration of microorganisms from the water due a negative
temperature differential between the water and the fruits or vegetables. The use of
surfactants can adversely affect the sensorial properties of the products^ (Adams et
al., 1989; Beuchat, 2000). The disinfection effect of chlorine also depends on the
produce and on the contaminating microflora. The efficiency of chlorine and other
disinfectants is limited by the neutralization effect of fruit and vegetable tissue
components on the surface and also by inaccessibility of disinfectant to the microbial
cells in creases, crevices, pockets, and natural openings in the skin (Nguen-The and
Carlin, 1994). The application is therefore more efficient for aerobic microflora in
lettuce than in root vegetables and cabbages^ (Garg et al., 1990; Ahvenainen and
Hurme, 1994).^ Chlorine has very broad antimicrobial spectrum. It acts against molds,
yeasts, bacteria, algae, protozoa, and many viruses,^ but there are differences in
sensitivity of individual groups of microorganisms and of the strains. Several authors
have referred to the limited effectiveness of chlorine in suppressing growth of
Listeria monocytogenes in lettuce and cabbage^ (Skytta et al., 1996; Francis and
O’Beirne, 1997).^ In addition to the health concerns related to the use of chlorine
previously mentioned, limitations of its use in fruits and vegetables are related to
its potential reactions with some organic compounds that have been observed during
chlorination of drinking water. The amounts used during treatment of fruits or
vegetables are similar or higher than those in drinking water, but the concentration
of various organic compounds in tissue juice is incomparably higher. Trichlormethan
and chloroacetic acid as well as various disinfection byproducts (DBPs) produced
by chlorination of amino acids such as iso-butyraldehyde from valine, isovaleralde-
hyde from leucine, 2-methylbutyraldehyde from isoleucine, and phenylacetaldehyde
from phenylalanine were identified in chlorinated drinking water. Some of these,
especially the aldehydes, often cause unpleasant odors (Froese et al., 1999).
TABLE 10.8
Concentration of Undissociated
HOCl (%)
pH 0°C 20°C4 100 100
6 98.2 96.8
7 83.2 75.2
8 32.2 23.2
9 4.5 2.9
Source: Adapted from Beuchat, L.R., in Min-
imally Processed Fruits and Vegetables, Aspen
Publishing, Gaithersburg, MD, 2000, p. 63.