The ochratoxins (ochratoxin A and ochratoxin B) are produced by Aspergillus ochraceus, Penicillium verrucosum and Aspergillus carbonarius (Frisvad and Thrane, 2000). In warm climates, such as those found in West and Central Africa, ochratoxin production is more commonly associated with A. ochraceus than it is with P. verrucosum, which often produces ochratoxin A in temperate climates (Sweeney and Dobson, 1998). Ochratoxin A is the major metabolite found as a natural contaminant of cereal grains such as maize, barley, wheat, oats and rye (Shotwell et al., 1971, 1976). Aspergillus carbonarius grows at high temperatures and is more often associated with fruits, especially grapes.
Ochratoxin A is the more toxic of the two derivatives and is nephrotoxic, immunosuppressive, carcinogenic and teratogenic in all experimental animals tested (WHO, 1990). It has been classified as a Group 2B compound, i.e., possibly carcinogenic to humans (IARC, 1987). The toxin has been associated with endemic nephropathy which is a fatal renal disease found among rural populations in Croatia, Bosnia, Herzegovina, Serbia, Bulgaria and Romania.
Limited data exist on the occurrence of ochratoxin A in foods in Africa. In Ghana, studies of fermented maize dough found ochratoxin A in 5/20 samples at levels < 6.4 ng/g (Kpodo et al., 1996). In Nigeria, ochratoxin A was detected in moldy maize samples from the Plateau State and the highest level recorded was 150 ng/g (Gbodi et al., 1986). Four of 48 maize-based gruel samples used as weaning food for children admitted to the Wesley Guild Hospital in Ilesha, Nigeria contained ochratoxin A at low levels (Oyelami et al., 1996). Another study in Nigeria also detected the toxin in Tiger nuts (Adebajo, 1993). In Sierra Leone, ochratoxin A was detected in fermented sesame seeds ("ogiri") and moldy fish samples (Jonsyn, 1988).
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