Fundamental Food Microbiology, Third Edition - Fuad Fathir

446 FUNDAMENTAL FOOD MICROBIOLOGY
addition, damage to membrane, disruption of protein synthesis, reactions with
nucleic acids, and interference with metabolisms have been suggested.
The germicidal action of liquid chlorine and hypochlorites is produced by
hypochlorous acid (HOCl). It probably enters the cell and reacts with the –SH group
of proteins. HOCl is stable at acid pH and is thus more effective; at alkaline pH, it
dissociates to H + and OCl – (hypochlorite ions), which reduces its germicidal effectiveness.
They are also less effective in the presence of organic matter. Chloramines
(inorganic or organic), such as Chloramine T, release chlorine slowly, but they are
less active against bacterial spores and viruses. They are effective, to some extent,
against vegetative cells at alkaline pH. Chlorine dioxide is more effective at alkaline
pH and in the presence of organic matter.
Chlorine compounds are fast acting against all types of microorganisms, less
costly, and easy to use. However, they are unstable (especially at higher temperatures
and with organic matter), corrosive to metals, can oxidize food (color, lipid), and
are less active in hard water. 1–4
2. Iodophores
Iodophores are prepared by combining iodine with surface-active compounds, such
as alkylphenoxypolyglycol. Because of the surface-active compounds, they are relatively
soluble in water. Iodophores are effective against Gram-positive and Gramnegative
bacteria, bacterial spores, viruses, and fungi. Their germicidal property is
attributed to elemental iodine (I 2) and hypoiodous acid, which oxidize the –SH group
of proteins, including key enzymes. They are more effective at acidic pH and higher
temperatures. In the presence of organic matters, they do not lose germicidal property
as rapidly as chlorine does. However, their effectiveness is reduced in hard water.
They are fast acting, noncorrosive, easy to use, nonirritating, and stable. However,
they are expensive, less effective than hypochlorites against spores and viruses, can
cause flavor problems in products, and react with starch. 1–4
3. Quaternary Ammonium Compounds
Quaternary ammonium compounds (QACs) can be used as detergent sanitizers
because they have cleaning properties along with germicidal abilities. However, they
are principally used as sanitizers. They are synthesized by reacting tertiary amines
with alkyl halides or benzyl chloride. The general structure is:
È R2
+ ˘
Í
��
˙
Í
˙
ÍR1
: N : R3˙Cl
or Br
Í
˙
Í
��
˙
Î
Í R4
˚
˙
– –