## 1 Introduction  
Citrus is one of the most widely produced fruits in the world, which mainly includes mandarin (_Citrus reticulate_), orange (_Citrus sinensis_), grapefruit (_Citrus paradisi_) and lemon (_Citrus limon_) [1]. During processing, large quantities of citrus peel waste is generated, which is an important source of bioactive compounds such as essential oils (EOs), flavonoids, carotenoids and vitamins [2]. Among them, citrus EOs are widely beloved for their delightful and invigorating aroma, making them in great demand in food, pharmaceutical, cosmetic and perfumery industries [2] and having promising market potential. Hence, the extraction of EOs is an effective way for the reclaimed utilization of citrus peel.  
The traditional extraction methods of EOs are cold pressing (CP) and steam distillation. The CP EO presents natural citrus aroma characteristics, since no chemical reactions occur in the extraction process that alter flavor composition. However, it contains some impurities such as pigments and waxes and has a low yield [3]. Hydrodistillation (HD) is also a commonly used method, with several shortcomings like long time consumption and losses of volatile compounds [4]. Therefore, some novel techniques were introduced such as microwave-assisted extraction [4; 5] and ultrasound-assisted extraction [6]. For example, microwave-assisted hydrodistillation (MADH) is one of the highly efficient and low energy consumption methods, as an excellent alternative for HD [7]. Anyway, noteworthy is the spinning cone column (SCC), an efficient counter-current liquid-gas contact extraction technology which emerged in recent years. It provides the advantages of high extraction efficiency, low residence time and a wide range of temperature control, thus greatly reducing the damage degree of heat-sensitive flavor compounds [8]. SCC has been applied in the food industry, including but not limited to the aroma recovery of tea and coffee [9], alcohol adjustment of wine [10] and extraction of essential oils [8; 11]. However, the application of SCC in citrus is still empty.  
'Huyou' (HY) is a unique citrus variety which is hybridized by _Citrus grandis_ ([PERSON] and _Citrus sinensis_ ([PERSON] [12]. It is mainly produced in Changshan country, Zhejiang Province, China. Compared to many other citrus species, HY EO exhibits stronger antibacterial activity, which may be related to the coexistence and content of D-limonene, \(\alpha\)-pinene, \(\beta\)-pinene, myrcene and ocimene [13]. Meanwhile, it shows strong antioxidant activity and has a potential to be used as a natural food preservative [13]. However, most studies on HY are focused on chemical constituents and its functional evaluation [14; 15]; there are very few studies on its flavor [13; 16]. Even though HY and graprefruit (GF) are both hybrids of pomelo and orange, their flavors still differ significantly. Yet, no comprehensive investigation has been conducted on the unique flavor of HY; thus, it remains unclear which specific aroma-active compounds contribute to the aroma differences between HY and GF.  
The flavoromics approach is an improvement over traditional flavor studies, providing a comprehensive and unbiased analysis of food flavor [17]. Moreover, the application of flavoromics enables flavor compounds to be correlated with sensory properties through high-resolution instrumental analysis and chemometrics [17; 18]. Thus, the objectives of this study are to (1) investigate the flavor difference of HY and GF EOs extracted by three different methods, (2) screen out the differential aroma-active compounds between HY and GF EOs using GC-O combined orthogonal partial least squares discrimination analysis (OPLS-DA) and (3) investigate the relationship between aroma-active compounds and sensory properties using partial least squares regression (PLSR).