Black olives as substrate for Aspergillus parasiticus growth and aflatoxin B 1 production

Abstract

Aflatoxin B1 (AFB 1) is a highly toxic and carcinogenic metabolite produced by certain Aspergillus species on agricultural commodities. Molds isolated from black olives are potentially toxigenic and present a potential health hazard. Olive oil originating from contaminated olives with AFB 1 might also be contaminated. The aim of this study was to investigate A. parasiticus growth and AFB 1 production in black damaged olives inoculated with 100 conidia flask −1 (1) treated with NaOCl 1.25%, (2) autoclaved at 110°C for 2 min, in comparison to the mold growth and AFB 1 production into the yeast extract sucrose (YES) medium under the same conditions of incubation and inoculation. AFB 1 extracted from cultures or olives and purified with immunoaffinity columns, was derivatized to its hemiacetal AFB 2a and then quantitated by HPLC using fluorescence detector. The recoveries and detection limits from YES and olives were 99.2%, 0.02 ng AFB 1 ml −1 and 94%, 0.15 ng AFB 1 g −1, respectively. Results showed that mycelia growth was not observed in olives during the 15 days of observation. The maximum growth of A. parasiticus on YES medium was shown on the sixth day. The AFB 1 production for both treated with NaOCl and autoclaved olives inoculated or not with A. parasiticus was not significantly different. On the other hand, AFB 1 levels produced in olives treated with NaOCl were significantly higher as compared with the autoclaved. The range of contamination of all olive samples inoculated or not for the whole period of observation was 0.15–2.3 ng AFB 1 g −1. The production of AFB 1 in YES medium on the third, the ninth and the 15th day was ∼1000-, ∼2500- and 10 000-fold higher, respectively, compared with the production in olives thus showing that black damaged olives of Greek origin are not a substrate favorable for AFB 1 biosynthesis at hazardous levels. Nevertheless, the production is possible at detectable amounts even after a little contamination that could happen randomly.