Food Poisoning Caused by Gram-Positive Sporeforming Bacteria
577
was produced at pH 4.2 in association with the mycelial mat.
90 In another study with the starting pH
of tomato juice at 5.8, the pH on the underside of the mold mat increased to 7.0 after 9 days and to
7.8 after 19 days.
51 The tomato juice was inoculated with type A botulinal spores, a Cladosporium
sp., and a Penicillium sp. The topmost 0.5 ml of product showed pH increases from 5.3 to 6.4 or 7.5
after 9 and 19 days, respectively. One type B strain was shown to produce gas in tomato juice at pH
5.24 after 30 days and at pH 5.37 after 6 days. In food systems consisting of whole shrimp, shrimp
pur´ ee, tomato pur´ ee, and tomato and shrimp pur´ ee acidified to a pH of 4.2 and 4.6 with acetic or citric
acid, none of three type E strains grew or produced toxin at 26
◦ C after 8 weeks.
96 Growth and toxin
production of a type E strain at pH 4.20 and 26
◦ C in 8 weeks was demonstrated when citric acid but
not acetic acid was used to control the pH of a culture medium.
122 In general, the pH minima are
similar for proteolytic and nonproteolytic strains.
With the use of aqueous suspensions of soy proteins inoculated with four type A and two type B
strains with incubation at 30
◦ C, growth occurred at pH 4.2, 4.3, and 4.4.
103 The inoculum was 5 ×
10
6 spores/ml, and 4 weeks were required for detectable toxin at pH 4.4 when pH was adjusted with
either HCl or citric acid. When lactic or acetic acid was used, 12 and 14 weeks, respectively, were
required for toxin at a pH of 4.4. Inocula of 10
3 –10
4 /g of botulinal spores represent considerably
higher numbers of these organisms than would be found on foods naturally (see below). That growth
may occur at a pH lower than 4.5 with large inocula does not render invalid the widely held view that
this organism does not grow at or below pH 4.5 in raw foods with considerably smaller numbers of
spores.
Regarding the interaction of pH, NaCl, and growth temperature, a study with Japanese noodle soup
(tsuyu) revealed that with types A and B spores, no toxin developed at (1) pH <6.5, 4% NaCl, and
20
◦ C; (2) pH <5.0, 1% NaCl, and 30
◦ C; (3) pH <5.5, 3% NaCl, and 30
◦ C; and (4) pH <6.0, 4%
NaCl, and 30
◦ C.
55
The minimum a w that permits growth and toxin production of types A and proteolytic B strains is
0.94, and this value is well established. The minimum for type E is around 0.97. Although all strains
have not been studied equally, it is possible that the other nonproteolytic strains have a minimum
similar to that of type E. The way in which a w is achieved in culture media affects the minimum values
obtained. When glycerol is used as humectant, a w values tend to be a bit lower than when NaCl or
glucose is used.
110 Salt at a level of about 10%, or 50% sucrose, will inhibit growth of types A and B,
and 3–5% salt has been found to inhibit toxin production in smoked fish chubs.
18 Lower levels of salt
are required when nitrites are present (see Chapter 13).
With respect to heat resistance, the proteolytic strains are much more resistant than nonproteolytics
(Table 24–3). Although the values noted in the table suggest that type A is the most heat resistant,
followed by proteolytic F and then proteolytic B, these data should be taken only as representative,
as heating menstra, previous history of strains, and other factors are known to affect heat resistance
(Chapter 17). Of those noted, all were determined in phosphate buffer. Among type E, the Alaska and
Beluga strains appear to be more heat resistant than others, and in ground whitefish chubs, D 80 ◦ C of
2.1 and 4.3 have been reported,
22 whereas in crabmeat, D 82.2 ◦ C of 0.51 and 0.74 have been reported,
respectively, for Alaska and Beluga.
76 With regard to smoked whitefish chubs, it was determined in
one study that heating to an internal temperature of 180
◦ C for 30 minutes produced a nontoxigenic
product,
31 whereas in another study, 10% or 1.2% of 858 freshly smoked chubs given the same
heat treatment were contaminated, mostly with type E strains.
91 (The heat destruction of bacterial
endospores is dealt with further in Chapter 17.)
With regard to type G, the Argentine and Swiss strains both produce two kinds of spores: heat labile
and heat resistant. The former, which are destroyed at around 80
◦ C after 10 minutes, represent about
577
was produced at pH 4.2 in association with the mycelial mat.
90 In another study with the starting pH
of tomato juice at 5.8, the pH on the underside of the mold mat increased to 7.0 after 9 days and to
7.8 after 19 days.
51 The tomato juice was inoculated with type A botulinal spores, a Cladosporium
sp., and a Penicillium sp. The topmost 0.5 ml of product showed pH increases from 5.3 to 6.4 or 7.5
after 9 and 19 days, respectively. One type B strain was shown to produce gas in tomato juice at pH
5.24 after 30 days and at pH 5.37 after 6 days. In food systems consisting of whole shrimp, shrimp
pur´ ee, tomato pur´ ee, and tomato and shrimp pur´ ee acidified to a pH of 4.2 and 4.6 with acetic or citric
acid, none of three type E strains grew or produced toxin at 26
◦ C after 8 weeks.
96 Growth and toxin
production of a type E strain at pH 4.20 and 26
◦ C in 8 weeks was demonstrated when citric acid but
not acetic acid was used to control the pH of a culture medium.
122 In general, the pH minima are
similar for proteolytic and nonproteolytic strains.
With the use of aqueous suspensions of soy proteins inoculated with four type A and two type B
strains with incubation at 30
◦ C, growth occurred at pH 4.2, 4.3, and 4.4.
103 The inoculum was 5 ×
10
6 spores/ml, and 4 weeks were required for detectable toxin at pH 4.4 when pH was adjusted with
either HCl or citric acid. When lactic or acetic acid was used, 12 and 14 weeks, respectively, were
required for toxin at a pH of 4.4. Inocula of 10
3 –10
4 /g of botulinal spores represent considerably
higher numbers of these organisms than would be found on foods naturally (see below). That growth
may occur at a pH lower than 4.5 with large inocula does not render invalid the widely held view that
this organism does not grow at or below pH 4.5 in raw foods with considerably smaller numbers of
spores.
Regarding the interaction of pH, NaCl, and growth temperature, a study with Japanese noodle soup
(tsuyu) revealed that with types A and B spores, no toxin developed at (1) pH <6.5, 4% NaCl, and
20
◦ C; (2) pH <5.0, 1% NaCl, and 30
◦ C; (3) pH <5.5, 3% NaCl, and 30
◦ C; and (4) pH <6.0, 4%
NaCl, and 30
◦ C.
55
The minimum a w that permits growth and toxin production of types A and proteolytic B strains is
0.94, and this value is well established. The minimum for type E is around 0.97. Although all strains
have not been studied equally, it is possible that the other nonproteolytic strains have a minimum
similar to that of type E. The way in which a w is achieved in culture media affects the minimum values
obtained. When glycerol is used as humectant, a w values tend to be a bit lower than when NaCl or
glucose is used.
110 Salt at a level of about 10%, or 50% sucrose, will inhibit growth of types A and B,
and 3–5% salt has been found to inhibit toxin production in smoked fish chubs.
18 Lower levels of salt
are required when nitrites are present (see Chapter 13).
With respect to heat resistance, the proteolytic strains are much more resistant than nonproteolytics
(Table 24–3). Although the values noted in the table suggest that type A is the most heat resistant,
followed by proteolytic F and then proteolytic B, these data should be taken only as representative,
as heating menstra, previous history of strains, and other factors are known to affect heat resistance
(Chapter 17). Of those noted, all were determined in phosphate buffer. Among type E, the Alaska and
Beluga strains appear to be more heat resistant than others, and in ground whitefish chubs, D 80 ◦ C of
2.1 and 4.3 have been reported,
22 whereas in crabmeat, D 82.2 ◦ C of 0.51 and 0.74 have been reported,
respectively, for Alaska and Beluga.
76 With regard to smoked whitefish chubs, it was determined in
one study that heating to an internal temperature of 180
◦ C for 30 minutes produced a nontoxigenic
product,
31 whereas in another study, 10% or 1.2% of 858 freshly smoked chubs given the same
heat treatment were contaminated, mostly with type E strains.
91 (The heat destruction of bacterial
endospores is dealt with further in Chapter 17.)
With regard to type G, the Argentine and Swiss strains both produce two kinds of spores: heat labile
and heat resistant. The former, which are destroyed at around 80
◦ C after 10 minutes, represent about