## 1 Introduction  
The mastic plant (_Pistacia lentiiscus_) is an evergreen shrub, belonging to the Anacardiaceae family [1]. Currently, it has two subspecies: _Pistacia lentiiscus_ L., which grows naturally as a shrub, and _Pistacia lentiiscus_ var. Chia, which is a cultivated subspecies [2]. It is commonly known as the mastic tree because it naturally produces a plant-based resin called mastic gum with a characteristic aroma from its trunk and branches [3]. The mastic gum produced by the _Pistacia lentiiscus_ var. Chia subspecies has a considerable economic importance and is recognized for its distinctive and unique quality as a spice [4]. Mastic gum has been used in traditional medicine since Ancient Greece for the treatment of various ailments, including cough, sore throat, eczema, and gastrointestinal diseases [5]. Additionally, due to its strong characteristic aroma, it is used as a flavoring agent in the food industry, particularly in chewing gums, sweets, and alcoholic beverages. The mastic tree is grown in various Mediterranean countries, including Turkiye, Greece, Tunisia, Morocco, Spain, and Italy [3, 6]. Mastic gum is exclusively produced on the Greek island of Chios, and is an important source of economic income. Although the mastic tree is widely distributed along the Aegean and Mediterranean coasts of Turkive, it does not contribute to the economy. These trees are at risk of extinction due to some factors such as declining agricultural activities, urbanization, tourism, lack of maintenance (pruning, etc. ), destruction, and aging of the trees [7; 8]. An aroma compound is a volatile substance detected in the human nasal cavity, contributing to the sense of smell. The aroma of a food item is formed by the interaction of hundreds of different volatile compounds, present in the food in concentrations ranging from \(\mu\)g/kg to ng/kg. It is one of the most important quality parameters affecting consumer preference. The aroma compounds that are naturally present in various parts of plants are categorized into chemical classes, including terpenes, aldehydes, alcohols, esters, and ketones [9]. These constituents are usually determined by gas chromatography-mass spectrometry instruments (GC-MS). Mastic gum contains numerous volatile compounds, predominantly terpenes and terpenoids. Researchers in various countries have identified major volatiles in mastic gum such as \(\alpha\)-pinene, \(\beta\)-pinene, \(\beta\)-myrrene, limonene, and \(\beta\)-aryophyllene [10; 11; 12]. Mastic gum has a distinct strong aroma and a woody, bitter taste due to these terpenes [13]. The terpenes present in mastic gum are influenced by various factors, including the geographical region where the tree is grown, the collection time, the duration between exudation from the stem and collection, climate conditions, and the extraction methods applied. These factors also affect the general quality of mastic gum [2; 13]. Some of these volatiles, known as the aroma-active compounds (AACs) or key odorants, are responsible for the characteristic aroma of the mastic gum. Despite being present in very low concentrations, these constituents significantly contribute to its distinctive odor and are detectable by the human nose. To identify these AACs, highly sensitive techniques such as GC-Olfactometry (GC-O) and/or GC-MS-O, which utilize the human nose as a detector, are commonly employed [14; 15]. Most of the previous studies have focused on the volatile constituents, phenolic compounds, and antioxidant activity of both mastic gum resin and its essential oils [2; 16; 17; 18; 19]. However, only a single study has explored the AACs in mastic gums [11]. To the best of our knowledge, this is the first study to comparatively evaluate the AACs of mastic gum samples from two different geographical origins (Turkije and Greece) by combining AEDA and sensory analysis.