Headspace analysis of volatile metabolites of Aspergillus ochraceus and Aspergillus parasiticus

Microbial spoilage is a major problem in grains or feedstuffs because it induces nutritional losses, formation of mycotoxins or potentially allergenic spores and in the end production of off-flavours. There is the need to find a method to conveniently assess the fungal growth in food and feed at every stage and after every technological process, as the detection of volatile compounds of fungi produced during primary and secondary metabolism. This paper presents the results of the analyses of some volatile compounds produced by Aspergillus ochraceus and Aspergillus parasiticus grown on maize. Moulds were cultivated on Czapek agar and on maize, previously sterilized by ultraviolet rays, in Erlenmeyer flasks closed with a Whatman bug stopper. Four samples for every substrate and mould were incubated at 26°C (A. ochraceus ) and 24°C (A. parasitucus) during 16 days. On day 8 and on day 16 of the trial, the headspace of the flasks containing the volatile metabolites was sampled with a Solid PhaseMicroextration (SPME) equipped with adsorbent Carbowax PDMS fibre (Supelco, USA). Headspace samples were analysed using a gas-chromatograph HRGCMega 2 series 8560 (Fison Instruments, Italy) equipped with a splitsplitless injector and a flame ionisation detector (FID). Separation of compounds of interest were done using a 30m x 0.25mm I.D. mm df capillary column TR-WAX with the following parameters: injection mode was splitless for 300 sec, injector temperature was 250°C, initial oven temperature 45° C, then raised at 3° C/min to 80°C, and kept for 20 min, then it was programmed at 2°C/min to 176° C followed by the raise al 10°C/min to 240°C and then kept for 20 min. The detector temperature was 260°C. The carrier gas was helium. Volatile compounds were identified by comparing their retention times to those of pure standards. The metabolites produced on Czapek agar by A. ochraceus were 3-Octanone, 1-Hexanol, 1-Octen-3-ol and 1-Butanol, by A. parasiticus only 3-Octanone and 1Hexanol, while the metabolites on maize were 3-Octanone and 1-Hexanol by A. ochraceus and 3-Octanone, 1Hexanol and 1-Octen-3-ol by A. parasiticus. The incubation time did not affect off flavour production in disagreement with the results from other authors (Borjesson, 1993; Magan and Evans, 2000). The two Aspergillus species did not show different volatile metabolites when cultivated on Czapek agar. Conversely, 1-Octen-3-ol was observed on maize substrate contaminated by A. parasiticus. The results of this analytical method open many possibilities to the employment of instruments, as electronic noses, for mould control in food and feed