Interacting Abiotic Factors Affect Growth and Aflatoxin B1 Production Profiles of Aspergillus flavus Strains on Pistachio-Based Matrices and Pistachio Nuts

Pistachio nuts are an economically important commodity produced by many countries. They can be colonized by mycotoxigenic fungi, especiallyAspergillus flavus, resulting in contamination withaflatoxins (AFs), especially aflatoxin B1(AFB1), a Class 1a carcinogen. The objectives were to examine the effect of interactions between the two key abiotic factors, temperature and water activity (aw) on (a)in vitrogrowth and AFB1production by four strains ofA. flavusisolated from pistachio nuts, on a milled pistachio nut medium modified ionically (NaCl) and non-ionically (glycerol) in the range 20–35°C and 0.995–0.85 aw, (b) colonization of layers of raw pistachio nuts stored at different interacting temperature x awconditions and on relative AFB1production and (c) develop models to produce contour maps of the optimal and marginal boundary conditions for growth and AFB1production by up to 4 strains of this species. On pistachio nut-based media, optimum growth of four strains ofA. flavuswas at 0.98–0.95 awand 30–35°C. Optimum AFB1production was at 30–35°C and 0.98 aw. No significant differences in growth was found on ionic and non-ionically modified media. Colonization of layers of raw pistachio nuts was slower and contamination with AFB1significantly less than inin vitrostudies. Contour maps based on the pooled data for up to four strains (in vitro,in situ) showed the optimum and marginal conditions for growth and AFB1production. These data can be used to identify those conditions which represent a high, intermediate or low risk of colonization and AFB1contamination in the pistachio nut processing chain. These results are discussed in the context of the development of appropriate intervention strategies to minimize AFB1contamination of this economically important commodity.