We report on the in vivo breath-by-breath analysis of volatiles released in the mouth during eating of ripe and unripe banana. The air exhaled through the nose, nosespace (NS), is directly introduced into a proton transfer reaction mass spectrometer and the time-intensity profiles of a series of volatiles are monitored on-line. These include isopentyl and isobutyl acetate, two characteristic odour compounds of ripe banana, and 2E-hexenal and hexanal, compounds typical of unripe banana. Comparing the NS with the headspace (HS) profile, two differences are outlined. First, NS concentrations of some compounds are increased, compared to the HS, while others are decreased. This indicates that the in-mouth situation has characteristics of its own—mastication, mixing/dilution with saliva, temperature and pH—which modify the aroma relative to an HS aroma. Second, we discuss the temporal evolution of the NS. While 2E-hexenal and hexanal steadily increase in the NS during mastication of unripe banana, no such evolution is observed in volatile organic compounds (VOCs) while eating ripe banana. Furthermore, ripe banana shows high VOC concentrations in the swallow breath in contrast to unripe banana.

Proton transfer reaction-mass spectrometry (PTR-MS) measurements on single intact strawberry fruits were combined with an appropriate data analysis based on compression of spectrometric data followed by class modeling. In a first experiment 8 of 9 different strawberry varieties measured on the third to fourth day after harvest could be successfully distinguished by linear discriminant analysis (LDA) on PTR-MS spectra compressed by discriminant partial least squares (dPLS). In a second experiment two varieties were investigated as to whether different growing conditions (open field, tunnel), location, and/or harvesting time can affect the proposed classification method. Internal cross-validation gives 27 successes of 28 tests for the 9 varieties experiment and 100% for the 2 clones experiment (30 samples). For one clone, present in both experiments, the models developed for one experiment were successfully tested with the homogeneous independent data of the other with success rates of 100% (3 of 3) and 93% (14 of 15), respectively. This is an indication that the proposed combination of PTR-MS with discriminant analysis and class modeling provides a new and valuable tool for product classification in agroindustrial applications.

Numerous publications have described measurements of breath isoprene in humans, and there has been a hope that breath isoprene analyses could be a noninvasive diagnostic tool to assess blood cholesterol levels or cholesterol synthesis rate. However, significant analytic problems in breath isoprene analysis and variability in isoprene levels with age, exercise, diet, etc., have limited the usefulness of these measurements. Here, we have applied proton transfer reaction-mass spectrometry to this problem, allowing on-line detection of breath isoprene. We show that breath isoprene concentration increases within a few seconds after exercise is started as a result of a rapid increase in heart rate and then reaches a lower steady state when breath rate stabilizes. Additional experiments demonstrated that increases in heart rate associated with standing after reclining or sleeping are associated with increased breath isoprene concentrations. An isoprene gas-exchange model was developed and shows excellent fit to breath isoprene levels measured during exercise. In a preliminary experiment, we demonstrated that atorvastatin therapy leads to a decrease in serum cholesterol and low-density-lipoprotein levels and a parallel decrease in breath isoprene levels. This work suggests that there is constant endogenous production of isoprene during the day and night and reaffirms the possibility that breath isoprene can be a noninvasive marker of cholesterologenesis if care is taken to measure breath isoprene under standard conditions at constant heart rate.