## 1 Introduction  
Tea is now the second-most popular alcohol-free beverage worldwide and has great economic importance. Remarkably, so-called blend-tea (scented tea and flavored tea) maintains its popularity in Europe, the USA, and also nowadays, in the Asia zone for its unique flavor and remarkable health benefits. A wide variety of blend teas which combined different teas and various plant sources have been developed in the sale markets, such as citrus tea (citrus and black, green and white tea, orange flavor), jasmine green tea (dry jasmine flower and green tea, floral), blend lavender tea (lavender and black or green tea, herbal and floral), blend peach oolong tea (peach and oolong tea, sweet and fruity), and blend rose black tea (dry rose and black tea, floral) etc. Among these blend teas, citrus black tea has a long history and remains popular among contemporary consumers [1]. For a long period, Chinese and European are accustomed to mixing black tea and citrus or its peel/oil seeking a fruit flavor tea. Nowadays, citrus species including _Citrus reticulate_ (citrus), _Citrus limon_ (lemon), _Citrus bergam_ (bergamot) were considered as the three main kinds of citrus blend black tea which we can get from the market [2; 3; 4; 5]. However, the citrus black teas were difficult to be distinguished by ordinary consumers for the similar flavor characteristics and consistent packaging (tea bags), which provide easy opportunities for counterfeiters to adulterate the ungraded citrus sources. Therefore, the discrimination of the citrus black tea with different species was urgent and challenging. The aroma is one of the important and determining factors of food. Hundreds of volatile components with different concentrations and odor characteristics comprise various types of aroma qualities of tea beverages [6; 7]. As in most citrus fruits, the hydrocarbon monoterene limonene (citrus-like, herbal odorant) contributes the most to the aroma quality of the corresponding citrus [8; 9]. Notably, blend tea behaved more complex in flavor comparing with the traditional pure tea, for the superimposed and interaction effects among the enormous odorants sourced for teas and plant materials [10]. However, little is known about the aroma profiles and characterized odorants in commercial citrus blend black teas, although volatile compounds in different varieties of citrus, pure black, jasmine, and some traditional Earl Grey teas (bergamot/bergamot oil and black tea) have been investigated [11; 12; 13; 14]. Interactions between odorants may be involved, but what impacts the unique flavor characteristics of teas blended with citrus remains obscure. Advances in analytical technology have led to the development of comprehensive two-dimensional chromatography-time-of-flight mass spectrometry (GC\(\times\)GC-TOFMS). This technology should be able to provide more comprehensive and precise chemical information about the aroma profiles of citrus black teas compared with a traditional gas chromatography-mass spectrometry [15]. However, although \(>\)5-fold more aromatic compounds could be separated by GC\(\times\)GC-TOFMS, the main contributors to the overall scents of teas could not be determined by single chemical analysis, owing to diverse odor thresholds and concentrations of aromatic components. Thus, the active compounds had to be determined by evaluating the detailed odor characteristics of each individual aromatic component of the tea samples. We recently identified the key odorants in chestnut-like green teas and four of the most famous black teas using GC\(\times\)GC-TOFMS combined with gas chromatography-olfactometry/mass spectrometry (GC-O/MS) [14; 16]. This provided a technical reference for comparisons of characteristic odorants in citrus black teas. Here, the study was aimed to differentiate and identify the aroma profiles and characterized odorants in citrus blend black tea with different citrus species by head space-solid phase microextraction (HS-SPME)/GC\(\times\)GC-TOFMS combined with GC-O/MS technique.