Stockpile Management to Minimize Aflatoxin Potential

Written by Bob Curtis, Almond Board of California
Recent studies supported by the Almond Board show there are clearly stockpile moisture conditions under which Aspergillus can grow with resulting aflatoxin contamination. This work is being led by Bruce Lampinen (UC Davis Extension Specialist) and and Themis Michailides (Plant Pathologist, UC Kearney Agricultural Center). Current guidelines were reviewed at the 2010 Almond Industry Conference seminar “Harvesting Clean and Safe” with presentations made by UC Farm Advisor Joe Connell and Bruce Lampinen.

Moisture Content, Stockpiling and Aflatoxin
Stockpile Management to Minimize Aflatoxin Potential
Recent studies supported by the Almond Board show there are clearly stockpile moisture conditions under which Aspergillus can grow with resulting aflatoxin contamination. This work is being led by Bruce Lampinen (UC Davis Extension Specialist) and and Themis Michailides (Plant Pathologist, UC Kearney Agricultural Center). Current guidelines were reviewed at the 2010 Almond Industry Conference seminar “Harvesting Clean and Safe” with presentations made by UC Farm Advisor Joe Connell and Bruce Lampinen.

• Stockpiling at a “total fruit” (in-hull almond) moisture content greater than 7% is problematic. This leads to an rH of greater than 70% within the pile -- which is the maximum rH for almond storage.
• Most critical is the outer portion of piles where there can be significant temperature fluctuation, condensation on tarps, and moisture accumulation.
• Of particular concern in these outer portions are the “green molds”, which include the Aspergillus mold that produces aflatoxin.
• This is not a uniform problem throughout high moisture content piles because the equilibrium rH within the piles comes to a steady state below maximum limits recommended for storage
• A practical guideline: Do not stockpile if either the hull moisture content exceeds 13% or the kernel moisture content exceeds 6%.

Managing Piles

• Orientation and shape of pile both can play an important role in minimizing condensation, mold growth and aflatoxin potential.
• Orienting the long axis of piles north/south is preferable. Condensation and mold growth tends to be worse on north side of piles with long axis oriented east/west.
• Smooth tops on pile helps minimize concentration of condensate and resulting mold growth.
• Results show tarp type/color can play an important role in minimizing temperature fluctuations and condensation.
• White-on-black is best at minimizing temperature fluctuations and the resulting condensation and mold problems. Consider using this for piles having higher moisture content in-hull product. Research shows white on black ran up to 40 degrees F cooler than clear, had much lower temperature fluctuations, and much lower condensation resulting in much less mold growth.
• Clear produces the highest temperature fluctuations and more potential for mold growth, but is fine for dry in-hull product.
• White is intermediate between clear and white-on-black.
• If piles are stacked too wet, it is important to open them up in the daytime when the relative humidity is lower and close them at night when the relative humidity is high.