Coupling in vivo MS nose-space analysis and sensory methods to investigate flavor release and perception

Introduction: Among the different human senses, flavor perception is one of the most complex since it involves smell, taste and chemesthesis. A complete disentanglement of the complex process of flavor perception is far from being achieved [1] but it has been accepted that its key drivers are the volatile organic compounds (VOCs) reaching the olfactory receptors [2]. Proton Transfer Reaction Mass Spectrometry provides a unique tool to monitor in real time VOCs ensuing from the retro-nasal pathway during in vivo food consumption [3]. Due to analysis rapidity and high sensitivity, the technique, together with other direct injection mass spectrometry techniques, has become a reference tool for the investigation of the phenomena related to flavor perception and release [1]. In the last years, the technique has been applied to different food matrixes [4-6] demonstrating its optimum coupling with dynamic sensory methods as Time Intensity (TI) and Temporal Dominance of Sensation (TDS). This short review describes several studies which coupled PTR-MS with dynamic sensory methods to better understand flavor perception and release phenomena in a variety of foods (chewing gum and mayonnaise). The first two studies investigated the influence of ingredient formulation and aroma concentration in chewing gums on aroma release and perception . The third study explored the effect of physiological parameters (oral cavity volume, salivary flow and papillary count), gender and ethnicity on flavor release and perception. The fourth study investigated the interplay of mayonnaise properties (fat content, viscosity) and carrier properties (hardness of bread and potatoes) and its impact on aroma release and perception. 2. Experimental In vivo nose-space analysis with two different PTR-MS machines (PTR-ToF-MS and PTR-QiTOF-MS, Ionicon Analytik, Austria) was applied. For the chewing gum studies sensory evaluation on flavor intensity and sweetness was performed by applying a discontinuous TI method at different time intervals. In the first two studies different gum formulations and aroma concentrations were tested by 10-12 trained panelists in replicate. For the third study a total of 30 panelists divided between Caucasian-European and Asian-Chinese evaluated the same type of chewing gum in triplicates. For the mayonnaise study dynamic perception of lemon intensity through TI and in vivo aroma release of two lemon aroma compounds (limonene, citral) were assessed by 14 trained subjects in triplicate for three mayonnaises consumed alone and in combination with bread and potato of different hardness. 3. Results In the first and second chewing gum study, significant differences in total aroma release (p < 0.05) were observed between different chewing gum formulations. In particular, it was observed that these differences were compound dependent and that PTR-MS signals are associated to a high variability reflecting panelists’ physiological differences. In-nose aroma concentration was proportional to the initial aroma concentration in the chewing gum. In the third study, ethnicity was found to have a significant effect on both in nose-space concentration and sensory perception. For different mass peaks associated to mint flavor compounds, Chinese panelists exhibited higher levels than European ones (p< 0.05) generally after 90 seconds of consumption and after the gum was removed from the mouth (Fig 1). The same trend was found in sensory perception both for flavor and sweetness. No significant differences were found between panelists of different gender. The product characteristics were also confirmed to have an effect on both flavor perception and release. In the fourth study, fat content and viscosity influenced dynamic release patterns of limonene and citral. Addition of carrier foods (bread, potato) decreased lemon perception intensity of all mayonnaises while, in some cases, it increased the in-nose concentrations. Harder bread decreases lemon intensity to a larger extent than softer bread, whereas only small effects of potato hardness on lemon intensity were observed. 4. Conclusions Real time mass spectrometry analysis by PTR-MS can detect and monitor in-vivo VOCs release during food consumption and can optimally support dynamic sensory methods providing an accurate time-resolved quantification of the sensory stimulus. Our results indicate a multimodal effect of aroma release on both flavor and sweetness intensity in chewing gum. The first two studies indicated a relevant impact of chewing gum characteristics (i.e aroma concentration and gum base composition) on flavor release. The third study highlighted that individual differences due to physiological, biochemical and physicochemical phenomena have a relevant effect in aroma release and thus in sensory flavor perception. Finally, the last study showed that both dynamic perception and in vivo aroma release of condiments are affected by condiment properties in a complex interplay with carrier food type and properties. The proposed in-vivo methods allow the dissecting of their complex interaction also in the case of real food.