AUTHOR=Baazeem Alaa , Garcia-Cela Esther , Medina Angel , Magan Naresh 

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.624007

DOI=10.3389/fmicb.2020.624007

ISSN=1664-302X

ABSTRACT=<p>Pistachio nuts are an economically important commodity produced by many countries. They can be colonized by mycotoxigenic fungi, especially <italic>Aspergillus flavus</italic>, resulting in contamination with <italic>aflatoxins (AFs)</italic>, especially aflatoxin B<sub>1</sub> (AFB<sub>1</sub>), a Class 1a carcinogen. The objectives were to examine the effect of interactions between the two key abiotic factors, temperature and water activity (a<sub><italic>w</italic></sub>) on (a) <italic>in vitro</italic> growth and AFB<sub>1</sub> production by four strains of <italic>A. flavus</italic> isolated 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 a<sub><italic>w</italic></sub>, (b) colonization of layers of raw pistachio nuts stored at different interacting temperature x a<sub><italic>w</italic></sub> conditions and on relative AFB<sub>1</sub> production and (c) develop models to produce contour maps of the optimal and marginal boundary conditions for growth and AFB<sub>1</sub> production by up to 4 strains of this species. On pistachio nut-based media, optimum growth of four strains of <italic>A. flavus</italic> was at 0.98–0.95 a<sub><italic>w</italic></sub> and 30–35°C. Optimum AFB<sub>1</sub> production was at 30–35°C and 0.98 a<sub><italic>w</italic></sub>. 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 AFB<sub>1</sub> significantly less than in <italic>in vitro</italic> studies. Contour maps based on the pooled data for up to four strains (<italic>in vitro</italic>, <italic>in situ</italic>) showed the optimum and marginal conditions for growth and AFB<sub>1</sub> production. These data can be used to identify those conditions which represent a high, intermediate or low risk of colonization and AFB<sub>1</sub> contamination in the pistachio nut processing chain. These results are discussed in the context of the development of appropriate intervention strategies to minimize AFB<sub>1</sub> contamination of this economically important commodity.</p>