Novel food applications of electronic nose technology for detection of spoilage fungi

Abstract

This work investigated the potential use of the electronic nose ( e-nose) for the rapid and early detection of fungal spoilage in intermediate moisture bakery products. Four xerophilic Eurotium spp., Penicillium chrysogenum and Wallemia sebi were grown on 2% wheat meal agar (WMA, 0.95 aw) at 25°C. Discrimination between the fungal species and the control media based on their volatile patterns was possible after 48h, using the Bloodhound BHl 14 e-nose. Volatile patterns produced by four Eurotium spp. and the Penicillium sp. were also investigated on WMA at different water activities (0.95, 0.90 and 0.85). Enzyme assays using p-nitrophenyl substrates were used as an indicator of spore germination and growth, and compared with volatile patterns and growth rates. Only three of the seven enzymes assayed were found to change significantly i.e. N-acetyl-P-D-glucosaminidase, a-D-galactosidase and P-Dglucosidase. Earlier detection and differentiation of the control blanks and the fungal species were achieved after 48h incubation, using the e-nose when compared to enzyme assays. In vitro study of volatile profiles from mycotoxigenic (Aspergillus flavus, A. ochraceus and W. sebi) and non-mycotoxigenic (A. niger and P. chrysogenum) fungi grown on WMA media demonstrated that differentiation of control blank media from the spoilage fungi was possible after 72h growth. Work on different mycotoxigenic and non-mycotoxigenic strains of Fusarium moniliforme and F. proliferatum showed that the e-nose could discriminate between the control blanks and the different strains after 48h growth. For all these studies the same three enzyme activities were found to be significant as in the previous work. Furthermore, the e-nose could detect fungal spoilage earlier than the enzyme assays. Volatile patterns produced by two Eurotium spp. and P. chrysogenum colonising a bread analogue modified to 0.95 aw at 25°C could be discriminated from the uninoculated bread after 40h incubation. This suggested that e-nose systems could be an earlier detection tool than enzyme assays. Furthermore, the same enzyme activities were found to be predominant as that observed for in vitro studies. E. chevalieri and P. chrysogenum were used to determine the limit of detection on a bread analogue (0.95 aw) using three inoculum concentrations (102 , 104 and 106 spores mr1 ). The initial spore concentration of 106 spores mr 1 treatments and the uninoculated bread analogue could be discriminated after 24h incubation. In another study, the volatile patterns produced by two Eurotium spp. and P. chrysogenum in the presence of potassium sorbate were measured. The uninoculated bread substrate and those colonised by the spoilage fungi could be discriminated after 48h growth. The study was repeated using calcium propionate and differentiation could be achieved only after 24h incubation. In the final study, volatile patterns produced by two Eurotium spp. and P. chrysogenum growing on natural bread substrate could be differentiated along with the uninoculated bread after 24h growth prior to any visible signs of growth. Overall, this study suggests that for the first time e-nose systems could be used to detect qualitative changes in volatile patterns for early and rapid detection of activity of the spoilage moulds in bakery products.