Volatiles for mycological quality grading of barley grains: determinationsusing gas chromatography-mass spectrometry and electronic nose

The possibility of using an electronic nose or gas chromatography combined with mass spectrometry (GC-MS) to quantify ergosterol and colony forming un its (CFU) of naturally contaminated barley samples was investigated. Each s ample was split into three parts for (i) ergosterol and CFU analysis, (ii) measurements with the electronic nose and (iii) identification of volatiles collected on an adsorbent with a GC-MS system. Forty samples were selected after sensory analysis to obtain 10 samples with normal odour and 30 with some degree of off-odour. The data set of volatile compounds and the data c ollected from the electronic nose were evaluated by multivariate analyse te chniques. SIMCA classification (soft independent modelling of class analogy ) was used for objective evaluation of the usefulness of the data from the GC-MS or electronic nose measurements for classification of grain samples a s normal or with off-odour. The main volatile compounds of grain with norma l odour were 2-hexenal, benzaldehyde and nonanal, while 3-octanone, methylh eptanone and trimethylbenzene were the main volatile compounds of grain wit h off-odours. Using data from the electronic nose three samples of 40 were misclassified, while data analysis of the volatile compounds detected with the GC-MS, led to six misclassified samples. Regression models (partial lea st-squares, PLS) were built to predict ergosterol- and CFU-levels with data from the GC-MS or electronic nose measurements. PLS models based on both G C-MS and electronic nose data could be used to predict the ergosterol level s with high accuracy and with low root mean square error of prediction (RMS EP). CFU values from naturally infected grain could not be predicted with t he same degree of confidence. (C) 2000 Elsevier Science B.V. All rights res erved.