Comparison of cultural and analytical methods for determination of aflatoxin production by Mississippi DeltaAspergillusisolates

Abstract

This study compared cultural and analytical methods for detecting aflatoxin production by Aspergillus species. Aspergillus isolates were obtained from various Mississippi Delta crops (corn, peanut, rice, cotton) and soils. Most of the isolates (99%) were A. flavus and the remainder comprised A. parasiticus and A. nomius. The following three cultural methods were evaluated on potato dextrose agar: fluorescence (FL) on beta-cyclodextrin-containing media (CD), yellow pigment (YP) formation in mycelium and medium, and color change after ammonium hydroxide vapor exposure (AV). Aflatoxins in culture extracts were confirmed by thin-layer chromatography (TLC) and quantified by enzyme-linked immunosorbent assay (ELISA). Of the 517 isolates, 314 produced greater than 20 ng/g of total aflatoxin based on ELISA, and 180 produced greater than 10 000 ng/g of aflatoxin in the medium. Almost all the toxigenic isolates (97%) were confirmed by TLC as producers. Of the toxigenic isolates, as determined by ELISA, 93%, 73%, and 70% gave positive FL, YP, and AV responses, respectively. Of the 203 isolates producing less than 20 ng/g of aflatoxin, 20%, 6%, and 0% of respective FL, YP, and AV methods gave false-positive responses. The 9% false-positive results from TLC fall within this range. This study showed good agreement among all tested cultural methods. However, these cultural techniques did not detect aflatoxin in all cultures that were found to produce aflatoxins by ELISA, LC/MS, and TLC. The best results were obtained when the AV color change and CD fluorescence methods were used together, yielding an overall success rate comparable to TLC but without the need for chemical extraction and the time and expense of TLC.

Detection of Aflatoxin B1 through indirect ELISA from fresh grains obtained from three maize growing zones of India

“…ELISA technique applied to the monitoring of AFB 1 contamination in the samples given by Abbas et al (2004). Extraction of sample: Weigh 25g ground sample with 2.5g salt (KCl) and place in blender jar.…”

Identification of a Major Xylanase from Aspergillus flavus as a 14-kD Protein

“…Non-toxigenic Aspergillus flavus isolate K49 (NRRL 30797, public access NCAUR collection) was isolated by H. Abbas from maize kernel material obtained from field studies [6]. This isolate was maintained on standard potato dextrose agar at 28°C.…”

Mycotoxins in animals: Occurrence, effects, prevention and management

“…The few TLC methods had been used for screening and not for quantification (Abbas et al, 2004;Benedetti et al, 2006). GC with highresolution MS had also been used for analysis of some mycotoxins (Fernandez et al, 2007;Ikonomou et al, 2008).…”

“…However, a labour-intensive derivatization step was often indispensable prior to GC analysis. Therefore, HPLC-MS-MS had increasingly become the method of choice for mycotoxin analysis (Abbas et al, 2004;Benedetti et al, 2006;Fernandez et al, 2007).…”