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An artificial neural network is used to predict both the classification of aroma compounds and their flavor impression threshold values for a series of pyrazines. The classification set consists of 98 compounds (32 green, 43 bell-pepper, and 23 nutty smelling pyrazines), and the regression sets consist of 24 green and 37 bell-pepper odorous pyrazines. The best classification of the three aroma impressions (93.7%) is obtained by using a multilayer perceptron network architecture. To predict the threshold values of bell-pepper fragrance, a standard Pearson R correlation coefficient of 0.936 for the training set, 0.912 for the verification set, and 0.926 for the test set is received with two hidden layers consisting of two and one neurons. The network for the threshold prediction of the class of green-smelling pyrazines with one hidden layer containing three neurons turns out to be the best with a standard Pearson R correlation coefficient of 0.859 for the training, 0.918 for the verification, and 0.948 for the test set. These good correlations show that artificial neural networks are versatile tools for the classification of aroma compounds.

AbstractThe essential oils isolated by hydrodistillation from the leaves or the flowering stalks of Cymbopogon citratus(DC) Stapf., C. giganteusChiov. and C. proximusStapf. syn. C. schoenanthus(L.) Spreng. subsp. proximus(A. Rich.) Maire & Weiller from Burkina Faso were analyzed by GC and GC/MS. The main constituents of the oil of C. citratuswere geranial (44.6%), neral (330%) and myrcene (10.7%). The oil of C. giganteuscontained limonene (17.3%) and a set of monoterpene alcohols: trans-p-mentha-l(7),8-dien-2-ol (17.0%), cis-p-mentha-l(7),8-dien-2-ol (16.5%), trans-p-mentha-2,8-dien-l-ol (13.8%) and cis-p-mentha-2,8-dien-l-ol (9.3%). The main component of the leaf and flower oils of C. proximuswas piperitone (59.1% and 55.6%, respectively). The essential oils of the three Cymbopogonspecies were also studied concerning their antioxidant and antiradical activity. Their properties were very low, compared to the two commercially used antioxidants tested (BHT and 5-tocopherol). C. proximusshowed the strongest antioxidant activity (Antioxidant Value = 1.54), followed by C. giganteus(A.V. = 1.04) and C. citratus(A.V.=0.11). On die other hand, the oil of C. citratuswas estimated to present the highest antiradical power, followed by C. proximusand C. giganteus.

Eight essential oils obtained by steam distillation from the scented leaves of Pelargoniumspecies and cultivars were added at 250, 500 and 1000 ppm to a quiche filling, inoculated with either Saccharomyces ludwigiior Zygosaccharomyces bailii(at 108cfu g−1), Salmonella enteriditisor Listeria innocua(at 109cfu g_1). The quiche fillings were then kept at 25 °C for 24 h and the residual number of micro‐organisms determined using the pour plate technique. There was an effective antimicrobial activity by the Pelargoniumessential oils at 250 ppm, comparable with that of commercial thyme oil, an excellent antimicrobial agent, against Saccharomyces ludwigiiand Zygosaccharomyces bailii, and a lesser inhibition compared with commercial thyme against Salm. enteriditis. There was a greater diversity of activity against L. innocua, which was in some cases more effective than commercial thyme oil. At 500 ppm, there was a greatly increased inhibition of microbial growth using the Pelargoniumessential oils, which was comparable with that of commercial thyme, clove, geranium and coriander oils. As there is no evidence for the toxicity of any of these novel Pelargoniumoils, and their odour does not make the delicately flavoured quiche filling unpalatable, there is a strong potential for their use in food processing.

The essential oil of Ocotea comoriensisKostermans (Lauraceae) was obtained from bark by hydrodistillation of plant material collected in the Comoros Islands. Analysis by GC and GC–MS indicates a terpenic chemical composition, with camphene, α‐pinene and bornyl acetate as the major components. The volatile extract did not reveal important antioxidant, larvicide or antimalarial properties. Copyright © 2002 John Wiley & Sons, Ltd.