Volatile metabolites produced by six fungal species compared with other indicators of fungal growth on cereal grains

Abstract

Six fungal species, Penicillium brevicompactum, P. glabrum, P. roqueforti, AspergiUusflavus, A. versicolor, and A. candidus, were inoculated on moistened and autoclaved wheat and oat grains. They were cultivated in glass vessels provided with an inlet and outlet for air. Air was passed through the vessels to collect volatile fungal metabolites on porous polymer adsorbents attached to the outlet. Samples were collected at two fungal growth stages. Adsorbed compounds were thermally desorbed, separated by gas chromatography, and identified by mass spectrometry. Differences in the production of volatile metabolites depended more on the fungal species than on the grain type. The fungal growth stage was not an important factor determining the composition of volatiles produced. 3-Methylfuran was produced in similar amounts regardless of the fungal species and substrate (oat versus wheat). The production of volatile metabolites was compared with the production of ergosterol and CO2 and the number of CFU. The production of volatile metabolites was more strongly correlated with accumulated CO2 production than with actual CO2 production and more strongly correlated with ergosterol contents of the grain than with numbers of CFU.

Microbiology of food taints

“…The principal problem associated with such infections is the production of mycotoxins rather than off-flavours and off-odours. However, many odorous fungal metabolites produced on grain cultures have been identified, but they have been studied as indicator compounds of fungal infections rather than as food taints (Borjesson et al, 1992).…”

Early detection of spoilage moulds in bread using volatile production patterns and quantitative enzyme assays

“…Bacterial species can be differentiated based on their volatile production patterns (Gibson et al 1997), although much less information is available on food spoilage moulds (Keshri et al 1998;. Some elegant studies have been carried out on the detection of spoilage fungi in grain (Borjesson et al 1990(Borjesson et al , 1992(Borjesson et al , 1993(Borjesson et al , 1996 and recently, both Schnurer et al (1999) and Magan and Evans (2000) reviewed this work. Correlations have been found for fungal contamination of grain with the level of ergosterol and with colony-forming units (cfu), and Magan (1993) hypothesized that the speci®c activity of hydrolytic enzymes was a good early indicator of the activity of spoilage moulds.…”

Use of an electronic nose for the early detection and differentiation between spoilage fungi

“…Better detection patterns were observed after 72 h incubation when growth was visible, but this is too late a stage for the use of an electronic nose for the early detection of mould activity in agrofood substrates. Previously, Borjesson et al (1990Borjesson et al ( , 1992 had found that there were differences in the fungal volatiles produced by grain fungi (Penicillium species, Aspergillus flavus, A. versicolor and A. candidus) using gas chromatography. Interestingly, there were fewer differences between grain substrate type and age of cultures than between species.…”

“…Recently, there has been interest in the potential of using the dominant odour volatiles produced by fungi, particularly 3-methyl-1-butanol, 1-octen-3-ol and 3-octanone, as indicators of spoilage in stored grain (Kaminsky et al 1985 ;Tuma et al 1989 ;Borjesson et al 1990). Indeed, Borjesson et al (1990Borjesson et al ( , 1992 found good correlation between odour volatiles detected by gas chromatography and CO 2 production and ergosterol, but not with colony forming units (cfu) for some Penicillium and Aspergillus species. Recently, Jonsson et al (1997) reported on the classification of grain quality using an electronic nose in combination with an artificial neural network.…”