Water activity and temperature effects on mycotoxin production by Alternaria arborescens.

VAQUERA, SANDRA; PATRIARCA, ANDREA; FERNÁNDEZ PINTO, VIRGINIA

Freising

Workshop; ICFM Workshop 2013; 2013

ICFM

Alternaria arborescens is the causal agent of tomato stem canker and it was also found in tomato fruits affected by ?black mold?. This species has been reported to produce the host specific AAL toxins together with some of the main Alternaria sp. toxins that can be found as food contaminants, alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TeA). AAL toxins (TA, TB, TC, TD and TE) have chemical structures similar to the carcinogenic Fusarium sp. toxins fumonisins. The objective of this study was to determine the effect of water activity (aw, 0.995, 0.975, 0.950) and temperature (6, 15, 20, 25 and 30°C) on mycotoxin production on a synthetic tomato medium of an inoculum of 105 spores of the reference strain A. arborescens EGS 39128. Mycotoxins determination was performed at 7, 14, 21, 30 and 40 days. Quantification of AAL TA toxin was made by HPLC with fluorimetric detection after derivatization with OPA. For AOH, AME and TeA determination the culture material was extracted with methanol and clarified with ammonium sulfate. The extracts of AOH, AME and TeA were analyzed by HPLC with UV photodiode array detector. AAL toxins TA and TeA were produced in higher levels than AOH and AME. The optimum AAL TA production (214 μg/g) occurred at 0.995 aw after 7 days of incubation at 15°C. A temperature of 15°C was the most favorable for AAL synthesis at all aw levels. The optimum conditions for TA accumulation (83.69 μg/g) were 0.975 aw and 30°C. These same environmental conditions were also the most favorable for AOH (0.63 μg/g, 40 days) and AME (0.45 μg/g, 14 days) accumulation. In general, high aw levels favored the mycotoxin biosynthesis. All toxins were detected at low levels at 6°C after the whole incubation period. A safe storage temperature for tomato fruits and high moisture tomato products (aw>0.95) in relation to A. arborescens toxins might be established below 6°C. The results obtained in the present work could be extrapolated to assess the health risk posed by tomato fruits and tomato products due to this pathogen and its toxins.