Personal dietary choices are largely based on flavor preferences. Thus understanding individual flavor perception and preference is vital to understanding the basis of human diet selection. We have developed novel tools to measure in real time and at an individual level volatile aroma compounds delivered breath-by-breath to the nose while eating and drinking. The same food may deliver different aromas to different people, due the specificities of their in-mouth environment (inter-individual differences). Moreover, a person may eat a given food in a different manner, leading to variations in the aroma profile reaching the nose (intra-individual differences). Understanding the basis of these differences opens the door to an individualized aroma science and the road to delivering nutritional value and health through products consumers prefer. The challenge to the food industry is to align what the consumer wants with what the consumer needs, delivering nutritional value and health through products they prefer.

We report on in-vivo breath-by-breath analysis of volatiles released in the mouth during eating of ripe and unripe banana using Proton Transfer Reaction-Mass Spectrometry (PTR-MS). The time-intensity profiles of isopentyl and isobutyl acetate, two key odour compounds of ripe, and (E)2-hexenal and hexanal, typical for unripe banana, are discussed. The questions we address is: how do retronasal aroma (nosespace, NS) and orthonasal aroma (headspace, HS) differ? Two main differences were noticed. First, the NS concentrations of some compounds are increased, compared to the HS, while others are decreased. Second, aroma in the mouth is dynamic, evolving with time. The in-mouth situation has characteristics of its own that may lead to an aromatic experience specific to the eating situation.

A recently developed technique, Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS), is reviewed based on applications on coffee. PTR-MS is a sensitive and fast method for on-line trace gas analysis. It consists of a specially designed chemical ionization cell, where headspace gas is continuously introduced and volatile organic compounds ionized by proton-transfer from H3O+. Protonated compounds are then mass analyzed in a quadrupole mass filter. First a description of the method will be given, with emphasis on the ionization mechanism. We then discuss a series of experiments that allow mass spectral intensities to be related to chemical compounds. Finally, two applications on coffee are discussed.