Jul. 31, 2007 - Jul. 31, 2008Award Number
Center for Produce SafetyInvestigator
Bruce D. Lampinen, Ph.D.
University of California, Davis
Almond stockpiles in Kern, San Joaquin and Glenn Counties were monitored during the fall 2007. Seven stockpiles were outfitted with temperature and relative humidity sensors at four depths in the stockpiles. Conditions were monitored at 1 to 3 minute intervals in the stockpiles throughout the storage period ranging from 84 to 150 days. When initial moisture content of nuts was low, mold growth in stockpiles was minimal and accordingly there was no aflatoxin detected. However, stockpiling of nuts with a water activity notably above the recommended 0.65 - 0.70 (= equilibrium relative humidity of 65 - 70%) resulted in significant mold growth near the pile surfaces. The two piles where this was observed had initial moisture contents of: 1) hulls 13.1% and kernels 5.2%; and 2) hulls 12.0% and kernels 7.3%. There was Aspergillus growth at the top and bottom edge of these stockpiles and analysis of one pile showed this was associated with aflatoxin production. This growth and aflatoxin production was associated with wetting of the nuts and hulls resulting from significant condensation of moisture on tarps that was observed in these areas. Significant mold growth and aflatoxin were only associated with these outer portions of the piles, because within the piles, the equilibrium relative humidity came to a steady state below the maximum limits recommended by current storage guidelines. The data generated in this first year of stockpile monitoring will make a substantial contribution to refining management guidelines for stockpiling that minimize potential for Aspergillus growth and resulting aflatoxin contamination of nuts.