Mechanisms of Food Additives, Treatments, and Preservation Technology 321
of whole and cut tomatoes. Significant reductions for whole and cut fruit were
obtained by dipping for 15 sec in a 1% solution and 4 to 15% solution, respectively
(Zhuang and Beuchat, 1996). In treatment of L. monocytogenes on shredded lettuce,
however, a 2% solution has almost no effect, and a more efficient treatment with a
10% solution affected the sensory quality of the lettuce (Zhang and Farber, 1996).
Cationic surfactants (quaternary ammonium compounds) are largely used for
sanitation of floors, walls, drains, equipment, and other food contact surfaces. The
addition of disinfectants to wash water can increase the safety and the shelf life of
produce. Washing with drinking water should not follow disinfection. The choice
of disinfectant depends on the legal requirements and also on the produce. The
disinfection treatment leads to the killing of a part of the surface microflora, but the
mode of action is not fully understood. A comparison of the efficiency of some
disinfectants against selected microflora of acidic foods is given in Table 10.9.
10.2.3.2 Direct Inactivation of Microorganisms: Abiosis
The microorganisms present in many food products are inactivated (killed) by
preservation treatment to the extent that prevents spoilage during the expected shelf
life (this is the concept of commercial or practical sterility).
10.2.3.2.1 Thermoinactivation
Thermal methods are extensively used for food preservation, including inactivation
of enzymes as previously discussed. The principle of the preservation effect is the
thermal denaturation of microbial proteins, which destroys the enzymes and enzyme-
controlled metabolism in microorganisms’ cells. Thermal treatment also leads to
other desirable changes such as protein coagulation, starch swelling, textural soft-
ening, and formation of aroma components. However, undesirable changes such as
TABLE 10.9
Comparison of Efficiency of Various Disinfectants and Preservatives Against
Selected Contamination Microflora of Acidic Food
Chemical Agent Saccharomyces Lactobacillus Leuconostoc Gluconobacter
Chlorine dioxide 0.0014 0.0031 0.0048 0.0031
Citric acid >10 >10 >10 6.3
Hypochlorite (Na) 0.027 0.03 0.034 0.031
Iodophor 0.0012 0.0039 0.0098 0.0039
Lactic acid >10 5 5.3 1.6
Peracetic acid 0.026 0.011 0.011 0.011
Quaternary ammonium compound 0.0012 <0.0001 <0.0001 0.0004
Dimethyl dicarbonate (DMDC)* 0.052 >0.1 >0.1 >0.1
- The application of DMDC is discussed in the “Abiosis” chapter (Chemosterilation) below
Note:Values are chemical concentrations (percentage weight per volume, aqueous) necessary to produce
an inactivation rate of 6 log cfu mL^1 min^1 for the indicated microorganism.
Source:Adapted from Winniczuk, P.P. and Parish, M.E., Food Microbiol., 14, 373, 1997.