Aflatoxin

Aflatoxin is the secondary metabolite produced by specific strains of Aspergillus, Aspergillus flavus and Aspergillus parasiticus. These species contaminate various agricultural commodities either before harvest or at post-harvest stages under favourable conditions of temperature and humidity.Aspergillus is a large genus of mould which grows at an optimal range of temperature of 28-33°C and at the water activity of about 0.83-0.97. The aflatoxigenic moulds, namely A flavus, A parasiticus and A nomius are principally found in soils and decaying vegetation. They occur in warmer parts of the world such as tropical region where temperature and moisture are high. They have a higher affinity of growth in nuts and oilseeds.

Characteristics of Aflatoxin

• Aflatoxin is classified into a number of subtypes. However, the most important ones are B1, B2, G1 and G2, distinguished by their fluorescenct colour under ultraviolet light. In addition, aflatoxin, M1 and M2 are hydroxylated metabolites of aflatoxin B1 and B2.
  
• Unlike Aspergillus, which often look greenish to the naked eyes, aflatoxins are odourless, tasteless and colourless. Chemically, they are stable in foods and resistant to degradation under normal cooking procedures. It is difficult to eliminate aflatoxin once it is produced.
  
• Accumulation of aflatoxin is dependent upon weather conditions. Before harvest, the risk for the development of aflatoxin is greatest during major droughts. When soil moisture is below normal and temperatures are high, the number of Aspergillus spores in the air increases. These spores infect crops through areas of damage caused by insects, and inclement weather. Once infected, plant stress occurs, the production of aflatoxin is favoured.
  
• During post-harvest stage, proliferation of aflatoxin can be exacerbated in susceptible commodities under storage conditions such as hot and humid storage environment.

http://www.fehd.gov.hk/safefood/report/aflatoxin/text_report.html