|
Toxin production in food
as influenced by pH, thermal treatment and chemical
preservatives
Oladipo, I. C.1*, Adebiyi, A. O.2
and Ayandele, A. A.2
1Science
Laboratory Technology Department, Ladoke Akintola University
of Technology, P. M. B. 4000, Ogbomoso, Nigeria.
2Pure
and Applied Biology Department, Ladoke Akintola University
of Technology, P. M. B. 4000, Ogbomoso, Nigeria.
*Correspondence author. E-mail:
xtiecoker@yahoo.com.
Accepted
11 April, 2008 |
|
Sixteen foods borne bacteria were isolated from raw food
samples including okro, carrot, spinach, pepper, tomato,
onion and cooked food samples (rice, yam, beans, meat and
plantain). The isolates were characterized and identified as
Bacillus brevis, Bacillus congulans,
Bacillus polymyxa, Bacillus lentus, Bacillus
megaterium, Bacillus subtilis, Acinetobacter
spp., Citrobacter freundii, Klebsiella
aerogenes, Streptococcus agalactiae,
Alcaligenes spp., Corynebacterium spp.,
Enterobacter aerogenes, Enterobacter spp.
and Staphylococcus epidermidis. These isolates were
screened on egg yolk agar for toxigenic properties and
thirteen of the sixteen were positive for toxin production
while three were negative. Six out of the thirteen toxigenic
bacterial were selected for further work. These were; E.
coli, K. aerogenes, C. freundii, B.
polymyxa, S. epidermidis and E. aerogenes.
The effect of pH, thermal treatment and chemical
preservatives on the growth rate and toxin elaboration of
E. coli, K. aerogenes, C. freundii, B.
polymyxa, S. epidermidis and E. aerogenes
was studied. It was observed that E. coli had no
viable growth until 48 h of incubation, while the other five
isolates had visible growth right from the 24 h of
incubation. Also E. coli did not produce toxin until
the 96th hour of incubation; K. aerogenes
and E. aerogenes were able to produce toxin at 24 h
of incubation, while C. freundii, B. polymyxa and
S. epidermidis produced toxin at 48 h of incubation.
Also, 44°C was not suitable for toxin production. pH 3 and 5
were less favorable for toxin production despite the fact
that isolates were able to grow at different temperature and
pH ranges. The isolate were more sensitive to sodium
metabisulfite than benzoic acid. Also, E. coli and
K. aerogenes were able to elaborate toxin in their
dormant state with 750 mg of sodium metabisulfite.
Key
words:
Toxin production, viable growth, raw food sample, cooked
food sample, E. coli, K. aerogenes, C. freundii,
B. polymyxa, S. epidermidis and E. aerogenes. |
