23 Mycotoxic Flora of Some Indigenous Fermented Foods
Felixtina E. Jonsyn
Fermented foods have a wide usage in Sierra Leone as
baby/weaning foods. Ogi(fermented maize/sorghum) and foofoo pap (fermented
cassava) are examples. Foofoo is also one of the two staples of the Creoles that
is now widely used by other tribes especially when rice is scarce. Ogiri
(fermented sesame seeds) is a favorite condiment used mostly by the poor as a
low-cost protein substitute. Several studies (1-4) have shown that toxigenic
fungi do not participate in the fermentation processes but contaminate the
product during or after the fermentation.
It has been demonstrated (1-4) that at times the substrate for
fermentation (maize, sesame seeds) has had prior exposure to mycotoxin. In the
case of maize, an aflatoxin B1 level of 200 ug/kg was reduced to 58 ug/kg in the
resulting fermented mashogi (5). The long cooking period (6 hours) of sesame
seeds before fermentation accounts for the loss of mycotoxins. Studies carried
out by Ogunsanwo et al. (6) have shown that losses of 64 percent aflatoxin B.
and 83 percent aflatoxin G1 could be observed in ogiri product prepared from
Aspergillus flavus-contaminated melon seeds.
In Sierra Leone, ogiri is produced by moist solid fermentation
of sesame seeds, a process similar to Nigerian ogiri, which is made from
fermented melon seeds (Citrullus vulgaris) (7) and Dawa-dawa from fermented
locust beans (Parlkia filicoidea) (8). Traditionally, the boiled seeds are
wrapped in jute bags and allowed to ferment for 4 to 5 days before smoke
treatment is applied. In such processes whitish threads are observed after day 2
and molds become obvious after 3 to 6 days (3).
This study was funded by the International Foundation for
Science, Stockholm, Sweden.
Microscopic examination of these whitish threads revealed the
presence of toxigenic and nontoxigenic Aspergilli and Perticillia species.
Detection of the corresponding mycotoxins of these toxigenic fungi in the
fermented, marketed, and stored ogiri(4) led to the present study to design
appropriate fermentation and storage techniques to reduce the risk of mycotoxin
MATERIALS AND METHODS
Sesame seeds were soaked overnight and pounded in a mortar to
dehull. The seeds were then washed and boiled for 6 hours. The boiled seeds were
divided into three portions. One portion was transferred to a clean dry nylon
fiber bag; the other was placed in a clean dry jute bag. Both were tightly
wrapped. The third was placed in a plastic bowl with a tight-sealed lid. Three
replicates of each of the nylon fiber and jute bag arrays were made. These were
divided into three groups. Group one was left to ferment for 5 days without
smoke treatment. Group two received early smoke treatment, from day 2 until day
5. Group three was smoked consistently from day 3 to day 8, and thereafter on
alternate days for 2 weeks.
Marketing and Storage
The three common methods for wrapping ogiri are (a) the use of
dried banana leaves Musa sapientum, (b) the use of fresh or smoked leaves of the
plant Newbouldia laevis, and (c) the use of small plastic wraps.
Leaf and plastic-wrapped ogiri samples bought from the local
markets were examined immediately under a stereo microscope. Samples with no
obvious fungal presence were selected. Three experimental designs were set up as
follows: (a) a set of six samples (three from each type of leaf wrap) was smoked
consistently for a week, (b) another set of six (two from each type of leaf and
plastic wrap) remained unsmoked and stored at room temperature, and (c) the
three types of wraps (minus ogiri) were placed in sterile plastic petri dishes
and stored at room temperature.
Determination of Mycotoxins
Twenty gram samples from each experimental design (jute and
nylon fiber bags) were analyzed for aflatoxin using the method of Kellert and
Spott (9). The modified method of Nowotny et al. (10) was used to screen 10-g
samples for the other mycotoxins.
The use of clean dry nylon fiber bags proved very effective.
Fermentation was observed to last 3 or 4 days. No fungal growth was noticed on
the outside of the bag or on the fermented product even on day 3 before smoke
Using jute bags, fermentation lasted 5 to 6 days, and evidence
of fungal contamination was obvious between days 2 and 3 of the fermentation.
But when the jute bags received smoke treatment from day 2 to the final day of
fermentation, no fungal contamination was observed. Whitish threads observed on
jute bags on day 3 disappeared when smoke treatment was applied. The use of
plastic bowls for fermentation was highly unsuitable because the process took
longer - 2 weeks.
When ogiri was smoked for 2 weeks, it had a very appealing aroma
and texture. In contrast, the end product from the plastic bowl experiment
lacked the characteristic ogiri aroma. When ogiri samples from both the jute and
nylon fiber bags were assayed for mycotoxins, there was no evidence of
Effect of the Types of Wraps
Samples wrapped in dry leaves of the banana plant were less
susceptible to fungal attack than ogiri wrapped in leaves of Newbouldia laevis.
However, regular smoke treatment reduced the incidence of fungal contamination
of ogiri in both types of leaf wraps. Plastic wrapped samples had no observable
fungi even up to 2 weeks of incubation but were devoid of the pleasant aroma
characteristic of the smoked product.
It has been clearly demonstrated in this study that the use of
clean dry nylon fiber bags instead of jute bags for the fermentation and early
smoke treatment of the fermenting mash contributed significantly to the
exclusion of fungi and thereby reduced the risk of mycotoxin contamination
during ogiri production. Further related studies on methods of improving
fermentation techniques on other products are now being considered.
1. Jonsyn, F. E. 1988. Mycopathologia 104:123-127.
2. Jonsyn, F. E. 1989. Mircen Journal 5:547-562.
3. Jonsyn, F. E. 1990. Mycopathologia 110:113-117.
4. Jonsyn, F. E. 1991. In press.
5. H. G. Muller, personal communication.
6. Ogunsanwo, B. M., O. O. Faboya, O. R. Idowo, T. lkotun, and
D. A. Akano. 1989. Die Nahrung 33:983-988.
7. Odunfa, S. A. 1981. Journal of Plant Foods 3:245-250.
8. Antai, S. P., and M. H. Ibarahim. 1986. Journal of Applied
9. Kellert, M., and H. J. Spott. 1980. Bundesgesundheitsblatt
10. Nowotny, P., W. Baltes, W. Kroenert, and R. Weber. 1983.
Chemie Mikrobiologie Technologie Der Lebersmitteln