The invention concerns a method and a device for measuring volatile substances in a global manner, with no prior separation of the different compounds. By xe2x80x9cglobal volatilesxe2x80x9d it is desired to signify that it is not necessarily a question of all the volatiles, but particularly a representative fraction of the set of volatiles released by an object. These volatile substances generally constitute the smell of a food or of an object. The measurement of the smell of a food or of an object in its global form represents a substantial advantage both quantitatively (intensity of the smell) and qualitatively (nature of the compounds constituting the smell). Although it is possible, as far, of course, as the key substances are known accurately, to quantitatively analyze the compounds constituting the aromatic profile of a product, it was not possible, until the development and perfecting of the techniques described below, to evaluate the volatile fraction in its global form. In the full assurance of this established fact, in the light of the results which have been obtained by virtue of the present invention, it can be considered that it is now possible to measure and quantitatively analyze, in a reproducible and reliable manner, this notion of xe2x80x9cfragrancexe2x80x9d.
The object of the invention is to create a method and a device of the type cited at the beginning which make it possible to obtain signals which are highly reproducible and also in agreement with the results of the sensory analysis. The object of the invention is resolved according to the present invention. The method of the present invention measures volatile substances in a global manner, with no prior separation of the different compounds, wherein the volatiles produced are collected by adsorption on adsorbent surfaces, the collected substances are next described directly in a detector, or desorbed and conveyed by means of an inert gas through a capillary tube which does not separate, or separates very little, to a detector, for a mathematical and/or statistical analysis of the signals obtained. The device of the present invention includes a head space for releasing the volatile substances, a system for collecting these volatile substances, a desorption system adapted to the collection system, a detection system and an evaluation system for interpreting the signals obtained.
The novelty of the invention consists of collecting volatiles, desorbing the molecules collected, transferring them without separating them and quantifying them by means of detectors. The diversity of the signals is obtained either by varying the sensors, or by varying the detection capabilities.
These concepts can be extended to volatile substances in solution by adsorption of these substances on sensors.
With the aim of quantitatively analyzing the global volatiles, with no prior separation of the different compounds, the idea arose of collecting these substances on a membrane, then desorbing this membrane directly in a detector. Most surprisingly, the signal delivered by the detector proved to be not only highly reproducible but also in perfect agreement with the results of the sensory analysis.
This technique therefore fully meets the expectations of the numerous researchers working in this field. In a recent publication dated March 1997, published in No. 129 of the CTIFL (Interbranch Technical Committee on Fruit and Vegetables), relating to the gustatory quality of peaches and nectarines, the authors (Danielle Scandella, Etienne Krauteler, Sophie Vxc3xa9nien) deeply regret that the measurement of global volatiles is still not possible xe2x80x9cThe physico-chemical measurements of firmness, sugar and acidity are not sufficient on their own to identify quality. The notion of fragrance, very important, is still not detectable by a device.xe2x80x9d