## 4 Discussion
However, the intensities of the NCS volatiles that could pass through the nasopharynx and be detected from the nose by the PTR-TOF-MS instrument were limited in both duration and strength, indicating that only a few aroma-active substances can be sensed after food consumption, thus affecting part of post-intake aroma enjoyment. The results revealed that volatile compounds were more prominently retained and perceived through retronasal pathways during in-mouth monitoring; this can be influenced by complex interactions during mastication, salivation, and temperature changes [20; 21]. In contrast, in-nose aroma release exhibited lower volatile concentrations, suggesting that the pathway to the nasal cavity may result in the loss of certain compounds [21]. The observed differences in the aroma release profiles of various ions in the NCS, particularly the intensity and rapid decline in the ion \(m/z\) 87.10 (dihydro-2(3H)-furanone and 2,3-butanedione) over seven breath cycles, underscore the complexity of aroma perception. This complexity could be influenced by the interactions between volatile compounds and food matrices as well as the physiological mechanisms of aroma release during ingestion [22; 23]. Accordingly, the volatile compounds that discharged ion \(m/z\) 87.10 could potently act as a buttery-caramel top-note to NCS, while other compounds, such as pyrazine, 2-methylpyrazine, 2-furanmethanol, and 5-methyl-2-furanmethanol, could provide nutty-roasted sweet base aromas [15; 16] (the aroma descriptions were also retrieved from [[http://www.thegoodscentscompany.com/](http://www.thegoodscentscompany.com/)]([http://www.thegoodscentscompany.com/](http://www.thegoodscentscompany.com/)), accessed on 20 October 2024). The retronasal kinetics of volatile compounds, such as the top or base (body) aroma, are important in flavor and sensory studies, particularly when using NCS as a raw material in various processed foods with different matrices, necessitating compatibility with other aroma-emitting compounds possessing distinct flavor qualities [24; 25]. The dynamic nature of aroma release and its dependence on the food matrix and processing conditions have also been observed in other food products, such as wine and coffee [23; 26]. This phenomenon highlights the importance of understanding aroma release kinetics and the impact of various flavor substances in shaping the overall sensory experience. The evaporation temperature influenced the sensory attributes of the NCS. As the temperature increased, the sensory intensities of the NCS tended to increase, and the most altered attributes were roasted aroma and bitterness, which could intensify its sensory perceptions. The increase in roasted aroma, which could be attributed to Maillard reaction products such as pyrazines [2; 16], aligns with the enhanced concentration of these compounds and their retronasal aroma releases in NCS produced at higher temperatures, notably NCS produced at 140 \({}^{\circ}\)C (Figure 4 vs. Table 1, Figure 3). This pattern demonstrates a correlation between higher heating temperatures and enhanced aroma development, most likely due to more apparent Maillard reactions and caramelization [14; 17]. On the other hand, the increase in the bitterness of the NCS obtained at higher temperatures could be attributed to sugar breakdown and bitter-tasting compound formation through thermal processing [14; 27]. Nonetheless, the balance between the roasted aroma and bitterness increase in the NCS might be an important factor in determining its acceptance requirements. Therefore, this study provides an important milestone for further practical applications of NCS products with varying flavor qualities and sensory properties, either consumed as table sugars or used as raw materials in processed foods and beverages.