The development of methods for the selective capture and characterisation of fragrances and flavours from nature

摘要

The chemical senses of taste and smell are the two least well understood of our senses. Recent advances in our understanding of the genetic and molecular mechanisms have led to increasing interest in olfaction and gustation. Amongst the practical applications of fragrances and flavours are commercial consumer products. The primary source for inspiration for these is nature and the work discussed in this thesis addresses methods for isolating selected aroma and taste molecules from natural sources, for use as new ingredients in food and fragrance applications. The methods are designed to deal with the challenges of isolating and identifying species present at very low concentrations (as low as parts per trillion), of unstable nature and with the desire to target specific functional groups. Carbonyl and thiol compounds have been selected for trapping due to their interesting fragrance and flavour characteristics respectively. A portable reactive trap has been designed, built, and tested to isolate aldehyde (or ketone) compounds from the headspace of living plants. The trap uses the derivatising reagent, 0-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride coated on to a solid sorbent, Tenax TA'-"'. Reagents with immobilised reactive groups capable of selective reacting with thiol compounds have been investigated and the proof of principle has been illustrated for three different methods. The nature identical status of the cooling compound, L-monomenthyl succinate, has been demonstrated by using highly sensitive and selective analytical techniques to identify this compound in the berries and leaves of plant Lycium barbarum. A preparative liquid chromatography system was used to simplify plant extracts which were subsequently analysed using nano liquid chromatography-electrospray ionisation-tandem mass spectrometry (nLC-ESI-MS/MS). This system could be applied to the analysis of other natural source extracts.