Impacts of Gaseous Ozone (O 3 ) on Germination, Mycelial Growth, and Aflatoxin B 1 Production In Vitro and In Situ Contamination of Stored Pistachio Nuts.

Pistachio nuts can become colonized by mycotoxigenic fungi, especially Aspergillus flavus , resulting in contamination with aflatoxins (AFs). We examined the effect of gaseous O 3 (50-200 ppm; 30 min; 6 L/min) on (a) in vitro germination, (b) mycelial growth, and (c) aflatoxin B1 (AFB 1 ) production on a milled pistachio nut-based medium at different water activity (a w ) levels and at 30 °C. This was complimented with in situ studies exposing raw pistachio nuts to 50-200 ppm of O 3 . Exposure of conidia to gaseous O 3 initially resulted in lower germination percentages at different a w levels. However, 12 h after treatment, conidial viability recovered with 100% germination after 24-48 h. Growth rates of mycelial colonies were slightly decreased with the increase of the O 3 dose, with significant inhibition only at 0.98 a w . The production of AFB 1 after O 3 treatment and storage for 10 days was stimulated in A. flavus colonies at 0.98 a w . Raw pistachio nuts inoculated with A. flavus conidia prior to O 3 exposure showed a significant decrease in population after 20 days of storage. However, AFB 1 contamination was stimulated in most O 3 treatments. The relationship between exposure concentration, time and prevailing a w levels on toxin control needs to be better understood for these nuts.