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 contamination.

MATERIALS AND METHODS

Fermentation Process

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.

RESULTS

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 treatment.

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 contamination.

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.

DISCUSSION

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.

REFERENCES

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 Bacteriology 61:145-148.

9. Kellert, M., and H. J. Spott. 1980. Bundesgesundheitsblatt 23(1/2): 13-21.

10. Nowotny, P., W. Baltes, W. Kroenert, and R. Weber. 1983. Chemie Mikrobiologie Technologie Der Lebersmitteln 8:24-28.