Abstract
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 degrees 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.