## 1 Introduction  
Coffee is one of the world's most consumed beverages. The consumption of coffee and its trade share has been increasingly ascending in China in recent years [1]. The chemical composition of raw coffee beans depends on many factors, such as varieties, origins, and planting conditions (soil, temperature, water, etc.) [2]. The sensory profile is a very important indicator of coffee quality, which can be evaluated based on the international coffee flavor wheel. The wheel was developed by the American Specially Coffee Association and divided into two parts including tastes and aromas [3]. Coffee drinks present a certain sour and bitter taste, of which the sour taste is mainly caused by organic acids such as citric acid and malic acid, and the bitter taste mainly comes from alkaloids, chlorogenic acid baking products, and Maillard reaction products. The aroma of coffee varied significantly among the samples. Raw coffee beans are green and beauty, but roasted coffee beans appear brown or tan in color, with consumers' preferring roasted, nutty, floral, chocolate, etc. So far, more than 1000 volatile compounds have been found in coffee, such as pyrazines, furans, ketones, aldehydes, etc., and various volatile compounds work together to produce the coffee-specific aroma [4].  
The coffee flavor is affected by the processing technology (baking temperature and time), storage conditions, grinding and brewing process, etc. [5; 6; 7]. The typical attractive flavor of roasted coffee beans is mainly generated by the Maillard reaction, Strecker degradation, caramelization, and pyrolysis reactions during the high-temperature roasting process [8; 9]. The preparation conditions include the grinding particle size of the roasted coffee beans and the temperature of the hot water poured over the ground coffee, which also affect the level of extracted coffee flavor components [10].  
Some sulfur-containing compounds, such as 2-furfurfurylthiol, methanethiol, and 2-methyl-3-furanthiol, as well as furrans and pyrazines, are among the most significant volatiles in terms of coffee flavor, and extremely influence the sensory profile of coffee [11; 12; 13]. The sulfur-containing compounds, furans, and pyrazines are at low concentration levels in coffee, but their extremely low odor thresholds mean that they have a great olfactory impact. Gas chromatography-ion mobility spectrometry (GC-IMS) and electronic nose (E-nose) has been used to identify and distinguish volatile compounds in coffee from different origins through principal component analysis (PCA) [14]. However, the traditional one-dimensional GC (1D-GC) has defects of poor separation, insufficient peak capacity, and serious co-current interference. In recent years, two-dimensional gas chromatography-time-of-flight mass spectrometry (GC\(\times\)GC-TOF/MS) has been widely used due to its stronger peak separation ability, especially in separating numerous subtle volatiles in complex sample matrices [15]. It has better shape quality, higher peak purity, and increased accuracy of qualitative and quantitative data [15]. The chromatographic peaks are gathered in a two-dimensional (2D) plane by two columns, so each volatile has two retention indexes with a stable position. Since GC\(\times\)GC-TOF/MS can analyze thousands of components in a short time due to its extremely high spectral generation rate (up to 500 spectra/s), it has been applied to study the flavor of Baijiu [16], Chinese dry-cured hams [17], and brewed coffee [18; 19].  
Therefore, the objectives of the study were (1) to characterize the volatile organic compounds (VOCs) of three commercially available coffee products in three states (bean, powder, and brew); (2) to compare the VOCs produced in complex coffee matrix by GC\(\times\)GC-TOF/MS method and GC-TOF/MS method, and (3) to investigate the subtle but important aroma contributing compounds, such as sulfur-containing compounds, furans, pyrazines in varied coffee samples.