Characterisation of the most odour-active compounds in a peel oil extract from Pontianak oranges (Citrus nobilis var. Lour. microcarpa Hassk.)

Abstract

Isolation of the volatile fraction from the peel of Pontianak orange (Citrus nobilis var. Lour. microcarpa Hassk.) by a careful solvent extraction/vacuum distillation process followed by application of an aroma extract dilution analysis (AEDA) revealed 32 odour-active compounds in the flavour dilution (FD)-factor range of 4–2048, 26 of which could be identified. On the basis of high FD-factors, (R)/(S)-linalool, myrcene, (R)-limonene, and 1,8-cineole were characterised as the most potent odorants, followed by octanal, (E,E)-2,4-decadienal, nerol, (E)-2-dodecenal, geraniol, and (E,E)-2,4-nonadienal. In addition, one odorant resembling the characteristic sulphurous, resinous aroma of the Pontianak peel oil was detected with a quite high FD-factor of 128. By mass spectrometry followed by synthesis, 1-phenylethanethiol exhibiting an intense sulphurous, resinous smell at the very low odour threshold of 0.005 ng/L in air, was found to be responsible for the odour impression detected in the extract. 1-Phenylethanethiol occurring as a mixture of the (R)-(76%) and the (S)-enantiomer (24%) has previously not been reported as odorant in foods. Application of static headspace aroma dilution analysis (SHA) on Pontianak peel revealed the green, grassy smelling odour-active compounds hexanal and (Z)-3-hexenal as further important odorants in the headspace above the peels.