308 Modern Food Microbiology
caused by Clostridium butyricum and C. tyrobutyricum. It is effective against other clostridia, including
C. sporogenes and C. perfringens, which are often employed in laboratory studies to assess potential
antibotulinal effects not only of nitrites but of other inhibitors that might have value as nitrite adjuncts
or sparing agents.
161
The Perigo Factor
The almost total absence of botulism in cured, canned, and vacuum-packed meats and fish products
led some investigators in the mid-1960s to seek reasons as to why meat products that contained viable
endospores did not become toxic. Employing culture medium, it was shown in 1967 that about ten
times more nitrite was needed to inhibit clostridia if it were added after instead of before the medium
was autoclaved. It was concluded that the heating of the medium with nitrite produced a substance or
agent about ten times more inhibitory than nitrite alone.
147,148 This agent is referred to as the Perigo
factor. The existence of this factor or effect has been confirmed by some and questioned by others.
Although the Perigo factor may be questionable in cured and perishable cured meats, the evidence for
an inhibitory factor in culture media involving nitrite, iron, and SH groups is more conclusive.
194
This inhibitory or antibotulinal effect that results from the heat processing or smoking of certain
meat and fish products containing nitrite warrants the continued use of nitrite in such products. The
antibotulinal activity of nitrite in cured meats is of greater public health importance than the facts of
color and flavor development. For the latter, initial nitrite levels as low as 15–50 ppm have been found
to be adequate for various meat products, including Thuringer sausage.
43 Nitrite levels of 100 ppm
or more have been found to make for maximum flavor and appearance in fermented sausages.
111 The
antibotulinal effect requires at least 120 ppm for bacon
18,35 comminuted cured ham
34 and canned,
shelf-stable luncheon meat.
32 Many of these canned products are given a low heat process (F 0 of
0.1–0.6).
Interaction with Cure Ingredients and Other Factors
The interplay of all ingredients and factors involved in heat-processed, cured meats on antibotulinal
activity was noted about 40 years ago and several investigators have pointed out that curing salts in
semipreserved meats are more effective in inhibiting heat-injured spores than noninjured.
49,160 With
brine and pH alone, higher concentrations of the former are required for inhibition as pH increases,
and Chang et al.
32 suggested that the inhibitory effect of salt in shelf-stable canned meats against heatinjured spores may be more important than the Perigo-type factor. With smoked salmon inoculated
with 10
2 spores per gram of C. botulinum types A and E and stored in O 2 -impermeable film, 3.8% and
6.1% water-phase NaCl alone inhibited toxin production in 7 days by types E and A, respectively.
145
With 100 ppm or more of NO 2 , only 2.5% NaCl was required for inhibition of toxin production by
type E, and for type A 3.5% NaCl + 150 ppm of NaNO 2 was inhibitory. With longer incubations or
larger spore inocula, more NaCl or NaNO 2 is needed.
The interplay of NaCl, NaNO 2 , NaNO 3 , isoascorbate, polyphosphate, thermal process temperatures,
and temperature/time of storage on spore outgrowth and germination in pork slurries has been studied
extensively by Roberts et al.,
158 who found that significant reductions in toxin production could be
achieved by increasing the individual factors noted. It is well known that low pH is antagonistic to
growth and toxin production by C. botulinum, whether the acidity results from added acids or the
growth of lactic acid bacteria. When 0.9% sucrose was added to bacon along with Lactobacillus
plantarum, only 1 of 49 samples became toxic after 4 weeks, whereas with sucrose and no lactobacilli,
50 of 52 samples became toxic in 2 weeks.
189 When 40 ppm nitrite was used alone, 47 of 50 samples
caused by Clostridium butyricum and C. tyrobutyricum. It is effective against other clostridia, including
C. sporogenes and C. perfringens, which are often employed in laboratory studies to assess potential
antibotulinal effects not only of nitrites but of other inhibitors that might have value as nitrite adjuncts
or sparing agents.
161
The Perigo Factor
The almost total absence of botulism in cured, canned, and vacuum-packed meats and fish products
led some investigators in the mid-1960s to seek reasons as to why meat products that contained viable
endospores did not become toxic. Employing culture medium, it was shown in 1967 that about ten
times more nitrite was needed to inhibit clostridia if it were added after instead of before the medium
was autoclaved. It was concluded that the heating of the medium with nitrite produced a substance or
agent about ten times more inhibitory than nitrite alone.
147,148 This agent is referred to as the Perigo
factor. The existence of this factor or effect has been confirmed by some and questioned by others.
Although the Perigo factor may be questionable in cured and perishable cured meats, the evidence for
an inhibitory factor in culture media involving nitrite, iron, and SH groups is more conclusive.
194
This inhibitory or antibotulinal effect that results from the heat processing or smoking of certain
meat and fish products containing nitrite warrants the continued use of nitrite in such products. The
antibotulinal activity of nitrite in cured meats is of greater public health importance than the facts of
color and flavor development. For the latter, initial nitrite levels as low as 15–50 ppm have been found
to be adequate for various meat products, including Thuringer sausage.
43 Nitrite levels of 100 ppm
or more have been found to make for maximum flavor and appearance in fermented sausages.
111 The
antibotulinal effect requires at least 120 ppm for bacon
18,35 comminuted cured ham
34 and canned,
shelf-stable luncheon meat.
32 Many of these canned products are given a low heat process (F 0 of
0.1–0.6).
Interaction with Cure Ingredients and Other Factors
The interplay of all ingredients and factors involved in heat-processed, cured meats on antibotulinal
activity was noted about 40 years ago and several investigators have pointed out that curing salts in
semipreserved meats are more effective in inhibiting heat-injured spores than noninjured.
49,160 With
brine and pH alone, higher concentrations of the former are required for inhibition as pH increases,
and Chang et al.
32 suggested that the inhibitory effect of salt in shelf-stable canned meats against heatinjured spores may be more important than the Perigo-type factor. With smoked salmon inoculated
with 10
2 spores per gram of C. botulinum types A and E and stored in O 2 -impermeable film, 3.8% and
6.1% water-phase NaCl alone inhibited toxin production in 7 days by types E and A, respectively.
145
With 100 ppm or more of NO 2 , only 2.5% NaCl was required for inhibition of toxin production by
type E, and for type A 3.5% NaCl + 150 ppm of NaNO 2 was inhibitory. With longer incubations or
larger spore inocula, more NaCl or NaNO 2 is needed.
The interplay of NaCl, NaNO 2 , NaNO 3 , isoascorbate, polyphosphate, thermal process temperatures,
and temperature/time of storage on spore outgrowth and germination in pork slurries has been studied
extensively by Roberts et al.,
158 who found that significant reductions in toxin production could be
achieved by increasing the individual factors noted. It is well known that low pH is antagonistic to
growth and toxin production by C. botulinum, whether the acidity results from added acids or the
growth of lactic acid bacteria. When 0.9% sucrose was added to bacon along with Lactobacillus
plantarum, only 1 of 49 samples became toxic after 4 weeks, whereas with sucrose and no lactobacilli,
50 of 52 samples became toxic in 2 weeks.
189 When 40 ppm nitrite was used alone, 47 of 50 samples