# Effects of Three Different Withering Treatments on the Aroma of White Tea
## 1 Introduction  
White tea is primarily produced in Fujian Province, China, and is one of six major tea types consumed in China [1]. The flavor of white tea is the result of its unique processing. White tea is naturally withered and dried but is not fixed or rolled [2]. Withering is a key step that determines the quality of white tea by causing a series of changes in the internal composition of the tea leaves due to the gradual loss of water and the activation of various enzymes under certain external temperature and humidity conditions [3]. Various withering methods are used, including withering indoors, in a withering-tank, and under sunlight [4]. In indoor withering, the fresh leaves are placed on a bamboo plaque and allowed to wither naturally. In the withering-tank method, fresh leaves are laid thickly in a tank and heated with a blower. Finally, in sunlight withering, fresh leaves are laid on a bamboo plaque and placed outside in sunlight during the spring [5]. For black tea, red light withering treatments are used in the summer to improve the aroma of the tea significantly [6]. Moreover, short-term sunlight withering treatment can increase aromatic compounds in oolong tea [7]. Thus, specific withering treatments produce differences in the tea aroma.  
White tea is prized for its fresh and elegant aroma. Hexanal, linalool, (E)-2-hexanal, phenylethyl alcohol, benzaldehyde, and methyl salicate are the primary volatile compounds that determine the aroma of white tea [8]. The increase of free amino acids and the decrease of glycoside-bound volatile content during the withering process promotes the formation of the tea's unique aroma [9]. Increasing the withering time and the thickness ofthe spread leaves or using light-emitting diode light irradiation can improve the freshness and purity of the white tea aroma [10; 11]. Although numerous studies have investigated whitering treatment methods, the effects of different withering treatments on aroma have not yet been studied and remain unclear.  
Most investigations of white tea aroma use headspace solid-phase microextraction (HS-SPME) to extract and analyze volatile compounds. One such analysis that employed HS-SPME revealed that the aromas of four white teas of different tenderness exhibited significant differences in aroma [12]. A comparison of naturally aged white teas by using HS-SPME revealed that the rapid aging technique could enhance floral and herbal aromas [13]. However, HS-SPME is ineffective for extracting weakly volatile compounds [14]. Solvent-assisted flavor evaporation (SAFE) is a method that enables the isolation of volatile compounds from complex matrices in a low-temperature vacuum environment [15]. The volatile compounds extracted using SPME and SAFE were found to be mutually complementary in dried fermented sausages [16]. HS-SPME is effective for capturing intensely volatile compounds, whereas SAFE has poor performance for extracting these compounds because they tend to dissipate during the concentration process [14]. Combining HS-SPME with SAFE enables a more comprehensive analysis of the differences in volatile compounds between teas. To the best of our knowledge, no relevant studies have investigated the extraction of volatile compounds from white tea using HS-SPME and SAFE.  
The molecular sensory science approach is a powerful tool for choosing key odor-active compounds and revealing the reasons for differences in aromas between teas [17; 18]. In this study, white teas were collected by withered indoors (IWT), in a withering-tank (WWT), or under sunlight (SWT), and their volatile compounds were comprehensively extracted using SAFE and HS-SPME. The analysis was performed by combining a molecular sensory science approach with chemometric methods to compare the effects of the three withering treatments on the white tea aroma and to elucidate the reasons for any differences.