You cannot see, smell or taste aflatoxin in dried figs; only a laboratory analysis gives a definite answer. In the warehouse or at intake, however, figs that glow greenish-yellow under 365 nm UV light are set aside as suspect fruit that may contain aflatoxin.

Why is aflatoxin invisible?

Aflatoxin is a toxin produced by the moulds Aspergillus flavus and Aspergillus parasiticus. It has no colour, smell or taste, and neither drying nor heating destroys it.

So a fig that looks perfectly clean can still contain it, while many stained or blemished figs do not.

When does contamination happen?

The risk starts when the fig ripens on the tree and begins to lose moisture. It peaks while shrivelled figs fall to the ground and sit on the drying yard until fully dry. If humidity rises in storage, the mould can become active again. The critical stages are therefore drying and storage.

How are suspect figs sorted out?

Where the mould grows, it leaves kojic acid behind. Combined with an enzyme of the fig itself, this compound glows greenish-yellow under long-wave UV light. The method is known as BGYF (bright greenish-yellow fluorescence).

The glow can appear on the skin and also inside the fig’s cavity, so a doubtful fig is cut open and checked inside as well.

The Codex Alimentarius code of practice for dried figs recommends inspecting every incoming lot under long-wave UV light and removing the fluorescent figs.

What UV light shows, and what it does not

What glows is not the aflatoxin itself but a trace left by the mould. In a study on dried figs, UV sorting caught about 73 percent of the aflatoxin-positive figs. Some contaminated figs did not glow, and some glowing figs turned out to be clean.

UV sorting is therefore a pre-sorting step. Whether a lot is fit for sale or export is shown by the laboratory result.

A practical routine

When a delivery of figs arrives, check the lot at goods intake with a rechargeable lamp. Remove the suspect fruit that may contain aflatoxin, then send a sample to the laboratory. That way, suspect figs leave the lot before it goes into storage.

For goods intake and warehouse checks, see the AFLALED models.

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