## 3 Results and Discussion
### Key-Aroma Analysis by ROAV  
Thousands of volatile compounds have been identified in food, but few have significant contributions to food flavor. These significant compounds are known as key aroma compounds [28]. ROAV can be calculated according to compound relative content and threshold value and used to evaluate the contributions of compounds to food flavor [21]. In previous studies [34], we found that black and green tea products made from Fuliang summer tea have high contents of flavor compounds (polyphenylols, polysaccharides, and amino acids).  
The ROAV values of 28 volatile compounds exhibited ROAVs (Table 3). Six compounds showed significant contribution (ROAV \(\geq\) 1) in BT: hexanal (1.33), nonanal (1.79), decanal  
Figure 4: Volatile profiles of three tea samples. **(A)** The number of volatile compounds of different categories identified by GC-MS in three tea samples. **(B)** The proportion of volatiles of different categories identified by GC-MS of three tea samples.  
(15.63), linalool (100), geraniol (2.61), and \(\beta\)-ionone (1.65). This result indicated that the BT made from summer tea has the same key flavor compounds as Keemun black tea [25]. Linalool had the highest ROAV value. It has floral, fruit, green, and orange-like odors, and contributes to the flower and fruit aromas of BT. The second-highest was decanal, which has orange and sweet odors, and contributes to the aroma quality of BT due to its low threshold (0.1 \(\upmu\)g/kg). Geraniol with rose-like, sweet, and honey-like odors, and \(\beta\)-ionone with floral, sweet, fruity, and berry-like odors, mainly contributed to the floral aromas in BT. Hexanal, with grassy, green, and fresh odors, and nonanal, with floral, green, and lemon-like odors, are fragrance aldehyde compounds and may have played a major role in the fragrance of BT. In addition, seven compounds were found to have important effects on the aroma quality of BT (0.1 \(\leq\) ROAV \(<\) 1): dihydroactinidiolide (0.77), methyl salicate (0.76), benzeneacetaldehyde (0.65), \(\beta\)-homocycloctiral (0.47), safranal (0.40), 2-pentyl-furan (0.21), and d-limonene (0.13). Benzeneacetaldehyde, with floral and green odors, showed the highest aroma intensity in Assam black tea, whereas methyl salicate had the highest concentration in Ceylon black tea. Methyl salicate is the typical aroma characteristic of Ceylon black tea [26].  
Five compounds contributed significantly to the aroma of GT (ROAV \(\geq\) 1): nonanal (1.98), decanal (14.09), (E,E)-2,4-decdienal (14.29), linalool (100), and \(\beta\)-ionone (3.12). Linalool had the highest ROAV value, which is responsible for the flower and fruit aromas, and is high in many kinds of high-quality spring green tea products, such as Jingshan tea [35], Japanese green tea [36], and Xihu Longjing tea [33]. The second was decanal, which had orange and sweet odors, and contributed significantly to the aroma quality of GT due to its low threshold. In addition, (E,E)-2,4-decadienal, with cucumber and melon odors, and nonanal, with floral, green, and lemon-like odors, may have contributed to the fragrance of GT. \(\beta\)-Ionone, which has floral, sweet, and fruity odors, can enhance the sweet characteristic of Japanese spring green tea [36]. In addition, eight other compounds were found to have important effects on the aroma quality of GT (0.1 \(\leq\) ROAV \(<\) 1), including hexanal (0.98), heptanal (0.94), methyl salicate (0.73), dihydroactinidiolide (0.68), geraniol (0.60), 2-pentyl-furan (0.26), sulactone (0.16), and geranyl acetone (0.13). Geranyl acetone, which has a floral odor, is the odor-active compound in Japanese green tea and can be one of the markers for the overall quality evaluation of green tea [36]. Geraniol, which had rose-like and sweet odors, showed a high flavor dilution factor. It is the main aroma compound of Chinese green tea [5].