Six spoilage fungi (four Eurotium species, a Penicillium sp. and Wallemia sebi) were grown as spore lawn surface cultures at 0·95 water activity and 25 °C. Prior to and during visible growth (24 and 48, and 72 h), single cultures were enclosed in polyethylene bags, the head space was sampled with an electronic nose unit, consisting of 14 polymer sensors, and the data analysed. There was good replication between volatile patterns of the same species and using principal component, discriminant function and cluster analyses it was possible to differentiate between the agar blanks, three Eurotium spp., the Penicillium sp. and W. sebi during microscopic growth for the first time. This suggests that there is potential for the early detection of the activity of spoilage fungi in general, as well as possible differentiation between related xerophilic spoilage fungi, by detection of the patterns of volatile odours produced using an electronic nose system.
Aims: Early detection of spoilage fungi (two Eurotium spp., a Penicilliumchrysogenum species) in bread analogues over periods of 72 h at 25°C and 0·95 water activity was evaluated using volatile production patterns, hydrolytic enzyme production, and changes in fungal populations.
Methods and Results: Using an electronic nose system it was possible to differentiate between uninoculated controls and samples contaminated with P. chrysogenum within 28 h. After 40–48 h it was possible to differentiate between the Eurotium spp., P. chrysogenum and the control using Principal Component Analysis (PCA). Cluster analyses could differentiate between the control, P. chrysogenum and the Eurotium spp. after 40 h. Of seven hydrolytic enzymes examined after 48 h, the specific activities of three were significantly different from uninoculated control bread. There were also differences between the mould species in production of three enzymes. Penicillium chrysogenum populations increased fastest, from about 103 cfu g–1 to 106–107 cfu g–1 after 72 h. For the Eurotium spp. this increase was slower.
Conclusions: Overall, this study suggests, for the first time, that an electronic nose system using a surface polymer sensor array is able to detect qualitative changes in volatile production patterns for the early detection of the activity of spoilage moulds in bakery products.
Significance and Impact of the Study: Potential exists for application of such systems for microbial quality assurance in intermediate moisture food products.
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