Abstract
Fungi produce a variety of microbial volatile organic compounds (MVOCs) during primary and secondary metabolism. The fungus, Aspergillus flavus, is a human, animal and plant pathogen which produces aflatoxin, one of the most carcinogenic substances known. In this study, MVOCs were analyzed using solid phase microextraction (SPME) combined with GCMS from two genetically different A. flavus strains, an aflatoxigenic strain, NRRL 3357, and a non-aflatoxigenic strain, NRRL 21882. A PDMS/CAR SPME fiber was used over 30 days to observe variations in MVOCs over time. The relative percentage of individual chemicals in several chemical classes (alcohols, aldehydes, esters, furans, hydrocarbons, ketones, and organic acids) was shown to change considerably during the varied fungal growth stages. This changing chemical profile reduces the likelihood of finding a single chemical that can be used consistently as a biomarker for fungal strain identification. In our study, discriminant analysis techniques were successfully conducted using all identified and quantified MVOCs enabling discrimination of the two A. flavus strains over the entire 30-day period. This study underscores the potential of using SPME GCMS coupled with multivariate analysis for fungi strain identification.
Highlights
Aflatoxins are polyketide-derived, secondary fungal metabolites and only three Aspergillus species, A. flavus [1], A. nominus [2] and A. parasiticus [3], are known to produce these naturally carcinogenic compounds [4]
Our results clearly show that the production of microbial volatile organic compounds (MVOCs) is significantly affected by microbial species and growth cycles, and we know from the literature that growth conditions such as media, pH, humidity and temperature affect MVOC production [33]-[35]
Based on standard VOCs absorption data, the CAR/PDMS solid phase microextraction (SPME) fiber was considered to be the best fiber for A. flavus VOCs profiling
Summary
Aflatoxins are polyketide-derived, secondary fungal metabolites and only three Aspergillus species, A. flavus [1], A. nominus [2] and A. parasiticus [3], are known to produce these naturally carcinogenic compounds [4]. Crop losses are estimated to cost between $1 and $1.5 billion/year in the United States [5]. These losses do not account for livestock losses or the impact on human health or healthcare costs from exposure to the fungi or to the toxins. The US Food and Drug Administration (FDA) has set limits of 20 ppb total aflatoxins for interstate commerce of food and 0.5 ppb for milk [8]. The European Commission has set the limits of 15 and 10 ppb for total aflatoxins on groundnuts and dried fruits, respectively [7]. Many methods have been proposed and are in development for the detection of aflatoxins or A. flavus including those that identify the presence of the toxins and those that identify the fungus
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