In a recent survey of randomly selected commercial almond orchards throughout the state, UC-Davis researcher Themis Michailides, Kearney Ag Center, Parlier, reported at the 2009 Almond Industry Conference that all orchards included in the survey were found to have both Aspergillus flavus and Aspergillus parasiticus, the molds responsible for producing aflatoxin. In their research, Michailides and coworkers also established that NOW larvae found in mummy nuts were contaminated with toxigenic Aspergillus spp. and therefore carry the mold leading to aflatoxin contamination.
One method of controlling aflatoxin contamination being investigated is using atoxigenic (non-toxin forming) strains of A. flavus. These strains competitively displace the toxin-forming strains. Some non-toxin strains have been registered and are in use for crops. For example the AF36 strain is registered for cotton in Arizona and California. Ongoing research has shown that the atoxigenic strain AF36 is widespread among almond orchards. In trials where AF36 was applied, the strain established well and became the dominant strain in the soil, reducing the presence of toxigenic strains. This work will continue towards registration in almonds.
The latest in stockpile management and conditions that may contribute to the development of aflatoxin during stockpiling was discussed at the conference by UC Davis researcher Bruce Lampinen. Research indicates that there is variability in nut drying on orchard floors and in the windrow, and that sampling should take this variability into account.
Stockpiling in-hull almonds with a total moisture content greater than 6.5 percent to 7 percent is problematic.
Both orientation and shape of pile can play an important role in minimizing mold growth potential. Orienting the long axis of the pile north to south is preferable, and smoothing the tops of the pile can help minimize concentration of dripping condensate into "valleys."
Preliminary results suggest that tarp color may play an important role in minimizing condensation potential.
For more information on food safety issues, visit almondboard.com/foodsafety.