There are six main types of aflatoxin based on their chemical structures. Four of these are produced by Aspergillus species and been designated based on the color of their fluorescence when exposed to UV light:
- Aflatoxins G1 & G2 fluoresce yellow-green
- Aflatoxins B1 & B2 fluoresce blue
All four types are produced by A. flavus and A. parasiticus, although the fungi may produce different concentrations of the toxin in different places and times. For example, an A. flavus infected nut might be very high in B1 but low in G1, while another nut infected by the same fungus might have more G1 than B1.
Aflatoxins M1 & M2 are derived from aflatoxins B1 and B2, and are found in milk of lactating animals that feed on contaminated feed.
Aflatoxin B1 is the most toxic and is the type of most concern.