Comparison of the growth and aflatoxin production of Aspergillus parasiticus on in-shell, shelled and split almonds depending on water activity and temperature

Aspergillus parasiticus is a fungus that can infect almonds and produce carcinogenic aflatoxins (AF). The objective of this study was to determine the growth and total AF production of A. parasiticus on three types of almond kernels (in-shell, shelled and split) under different combinations of temperature (20, 27 and 35 degrees C), water activity (0.65, 0.75, 0.80, 0.85, 0.90, 0.95, 0.99 a(w)) and incubation period (10, 20 and 30 days). The in-shell kernels supported the least amount of growth and AF production. The fungus grew moderately at 0.90 and 0.95 a(w) and produced moderate (<50 <mu>g/kg) amount of total AF at 0.95 a(w) on in-shell almonds. On shelled kernels, growth was also limited to 0.90 and 0.95 a(w). Aflatoxin production reached high levels at 0.95 a(w) at all three temperatures on shelled almonds (324.3, 325.4, and 139.8 mu g/kg at 20, 27 and 35 degrees C, respectively). The fungus grew rapidly and produced high levels of AF (>300 mu g/kg) on split kernels over a wide range of conditions (0.80 to 0.95 a(w) and 20 to 35 degrees C). Contour plots revealed that the optimum conditions for AF production on split kernels were at 0.90-0.95 a(w) and 2027 degrees C. Aflatoxin production also depended on incubation time. By day 30, AF production on split kernels exceeded 300 mu g/kg at 0.80 a(w) at all temperatures. There was no fungal growth and AF production at 0.65 and 0.75 a(w). These findings indicate that maintaining low water activity (<0.75 a(w)) during transport and storage can reduce the risk of infestation and aflatoxin production by A. parasiticus on inshell, shelled and split almond kernels.