## 1 Introduction  
Green tea, the most widely consumed beverage in Asia, has recently become more widespread in the West where black tea is traditionally consumed. Green tea is made solely with the leaves of _Camellia Sinensis_ that have undergone minimal oxidation under processing. The popularity of green tea is due to many factors. Firstly, the biological value related to the high content of catechins with recognized antioxidant properties. Indeed, a number of epidemiological studies have shown that regular tea drinkers have a lower chance of developing cardiovascular disease, degenerative disorders and cancers [1, 2, 3, 4]. The manufacturing process of green tea includes steaming, characteristic of most of the Japanese teas, like Sencha, or pan-firing, typical of most of the Chinese teas, i.e., Bancha. During these processes, the oxidase enzyme, present in tea leaves, is inactivated, thus preserving the green color of the leaves and the catechin composition. Together with the claimedhealth-promoting effects, another contributory factor to green tea's popularity is its flavor. The pleasant smell of green tea depends primarily on the composition of the odorants and their transformation due to different treatments, including roasting, steaming, baking, sun-drying or storage conditions (Figure 1) [5,6]. For example, Hojicha is the name given to some green tea varieties that are subjected to a roasting process at a high temperature (from 160 to 200 \({}^{\circ}\)C), altering the leaf color from green to reddish-brown and the aroma. Hojicha is often made from Bancha, tea from the last harvest of the season, or from other varieties, including Sencha. The desirable flavor of Hojicha, mainly defined as \"roasty\", is due to the formation of pyrazines [5,7,8], however, the changes in the odorant composition also contribute to the characteristic aroma. Pyrazines and acrylamide are commonly generated via the Maillard reaction during the roasting process, giving roasted green tea a strong odor [9]. On the other hand, the high demand for green tea is also due to the presence of bioactive substances, mainly catechins, hence the Hojicha pan-firing process should be optimized to avoid catechin degradation [10,11] and high levels of acrylamide, which is probably carcinogenic to humans [12], without compromising the quality. Since commercial Hojicha tea contains a non-negligible amount of acrylamide, [PERSON] et al. have suggested roasting conditions (160 \({}^{\circ}\)C for 30 min, or 180 \({}^{\circ}\)C for 15 min) which minimize the formation of acrylamide but at the same time ensure the formation of pyrazines which contribute to the pleasant aroma [8]. In general, comparing the composition of Sencha Ariake tea, considered as a typical reference sample, Bancha Hojicha tea shows lower levels of catechins, the absence of both theanine enantiomers and a relatively high level of the distomer (\(-\))-catechin and of (\(-\))-gallocatechin gallate. This suggested that thermal epimerization of (\(-\))-epicatechin and (\(-\))-epigallocatechin gallate occurs [2]. Herein, an investigation was conducted on the variation in the composition of the main aromas of selected Bancha and Sencha tea and the formation of pyrazines following roasting. The roasting process was carried out at different temperatures (160, 180 and 200 \({}^{\circ}\)C) for 30 min in order to assess the impact on the composition of the tea. The roasted conditions were selected according to [PERSON] et al. [8]. To this end, qualitative analysis of the composition of 22 green teas (including Bancha and Sencha) and two black teas and quantitative analysis on the main odorants from tea infusion was performed by headspace-solid-phase microextraction gas chromatography (HS-SPME GC-MS) in total ion current (TIC) and in single ion monitoring (SIM) modes. Figure 1: Different tea production processes.