Aflatoxin & How to Avoid It

Aflatoxin is a toxic natural compound produced by certain molds; it can cause liver damage and cancer. Aflatoxin is found in many common foods, but only in small quantities is considered safe (U.S. ≤ 20 parts per billion (ppb), Europe ≤ 2 ppb). We at Desert Harvesters are specifically concerned with the invisible mold (Aspergillus flavus) that can produce aflatoxin B1 on mesquite pods, as well as on other food crops (legumes, corn, etc) that have been exposed to moisture.

(in higher elevations, harvesting in dry autumn weather may be an option)

Desert Harvesters is now recommending that, as much as possible, harvesters collect mesquite pods BEFORE the monsoon rains. (This can be more difficult at higher altitudes due to later ripening. In these areas the best practice may be to only harvest in dry autumn weather.) The reason for pre-rain/dry-season harvesting is to reduce the pods’ exposure to moisture, and thus the risk of the development of an invisible mold (Aspergillus flavus) and the aflatoxin it can produce. Aflatoxin poisoning can have serious health consequences over the long term, so we want to harvest in a SAFE manner. To further avoid moisture issues with the pods we recommend you do NOT rinse or wash pods.

See here for our current BEST-PRACTICES harvest tips.
See here for additional SAFE harvest recommendations.

In the small number of batches of mesquite flour we have tested thus far…
ALL mesquite pods we tested which were harvested BEFORE the rains have tested SAFE.
In other words, NO mesquite pods harvested BEFORE the rains had results with unsafe levels of aflatoxin. The U.S.-designated safe limit of aflatoxin is 20 parts per billion (ppb), so safe test results will be 20 or fewer ppb.

However, all test batches of mesquite pods that DID have results with unsafe levels of aflatoxin were harvested AFTER the onset of the rains. Again, in the U.S., safe aflatoxin levels of 20 or fewer parts per billion (ppb) are considered safe. However, many other batches harvested AFTER the onset of the rains tested SAFE.

See here for a poster highlighting the results of a study examining, in particular, the relationship between harvest date (relative to monsoonal rains) and aflatoxin levels in mesquite flour in the Tucson area. Study by Nicholas Garber, PhD (University of Arizona School of Plant Sciences); Jeau Allen (Aravaipa Heirlooms); and P.J. Cotty (USDA-ARS).


Harvesters can have their milled mesquite flour tested at our 14th Annual Mesquite Milling on June 23, 2016, in Tucson. The cost per test will be a special subsidized fee of only $5.

The test kit that we will be using is called Reveal for Aflatoxin (Neogen product #8015). It does not tell you how many parts per billion (ppb) of aflatoxin is in a sample, it provides only a yes/no result (similar to a pregnancy test stick) as to whether the sample contains more/fewer than 20 ppb of aflatoxin. Click for the Reveal for Aflatoxin Technical Information sheet. Click for the Reveal for Aflatoxin Procedure instruction sheet on how to run the test. If you come to our pod training on June 18, 2016, you’ll get to learn how to use the test kit.

Harvesters also have the option of having their milled mesquite flour tested by a University of Arizona lab for a $33.00 fee. This test, while more expensive, does provide a specific reading of how many parts per billion (ppb) of aflatoxin your sample contains. You’ll get your results within about a week.

Contact the testing lab at:
Sadhana Ravishankar, Ph.D.
School of Animal & Comparative Biomedical Sciences
1117 E. Lowell Street, Rm 218
PO Box 210090
University of Arizona
Tucson, AZ 85721
Phone: (520)- 626-1499
Fax: (520)-621-6366

Information to record when you harvest
Next time you harvest, note the location of harvest, the date, whether you harvested before or after the rains, and how you harvested (directly off the tree, off the ground, etc). Please submit this info with any samples you submit for testing so we can enlarge our data set for the benefit of all. The University lab keeps all information confidential, so the only way we can enlarge our data pool is if you also share your harvesting info (where and when harvested, how harvested—off tree or ground or both) and test results with us. You can email us with this info at

If you harvest some pods before the rain and some after, try to keep these batches separate and test them separately. You could do the same for different harvesting methods – those harvested directly from tree or those harvested off the ground.


To encourage harvesting before the monsoons, and to be more in sync with the Sonoran Desert ecology’s natural patterns, Desert Harvesters has shifted its annual harvesting and milling trainings, along with its mesquite millings and fiesta, to the month of June—BEFORE the summer rains. This is also when our native bean trees (mesquite, desert ironwood, palo verde) are ready to harvest (they produce before the rains so their seed is on the ground ready to germinate when the rains arrive). Regularly check our Calendar of Events for more such event info.

We hope to continue to share more studies and best harvesting practices.

Check back to this page for updates.

1 Comment

Post a Comment