## 2 Materials and Methods
### GC-MS Analysis  
GC-MS analysis of green huajiao followed the method of a previous study [28]. The volatile compounds in the green huajiao samples were analyzed and identified by GC-MS (7890A-5975C, Mettler-Toledo Instruments Shanghai Co., Ltd., Shanghai, China). A chromatographic column HP-5 MS (30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m, Agilent Technologies, Santa Clara, CA, USA) with a constant purge flow rate of 1.5 mL/min was used for chromatographic separation and identification of VOCs in the samples. The initial temperature of the column was 65 \({}^{\circ}\)C, ramped up to 90 \({}^{\circ}\)C at 25 \({}^{\circ}\)C/min and held for 1 min, ramped up to 105 \({}^{\circ}\)C at 1 \({}^{\circ}\)C/min and held for 2 min, ramped up to 200 \({}^{\circ}\)C at 3 \({}^{\circ}\)C/min and held for 2 min, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Attributes** & **Definition** & **Reference Compounds** \\ \hline Citrusy & A compound aroma such as citrus, orange, grapefruit & 2 mL/L orange essence solution \\  & and other citrus fruits. & 1 mg/L geraniol alcohol-water solution \\  & A typical character of fresh fruit, vegetables or grasses, with an under-ripe odor & 2.5 mL/L cis-3-hexen-1-ol solution \\  & A pungent odor similar to that of herbal plants & 0.4 mg/L cuminol alcohol—aqueous solution \\  & Compound aroma of lemon-like fruit characteristics & 2 mL/L lemon essence solution \\  & combined with acidity and gives a feeling of freshness & 2 mL/L lemon essence solution \\  & and pleasant sensation & \\  & A stimulating odor with a cooling sensation, with a & 2 mL/L mint essence solution \\  & distinct filling of freshness & 2 mL/L cinnamaldehyde solution \\  & An irritating odor caused by spices such as anise, cinnamon, chilli and others & 2 mL/L vanilla essence solution \\  & Sweet & A sweet and aromatic odor, similar to vanilla & 2 mL/L vanilla essence solution \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Aroma descriptors, definitions and reference samples for sensory evaluation. and ramped up to 250 \({}^{\circ}\)C at 30 \({}^{\circ}\)C/min and held for 2 min. The carrier gas was helium, and the sample was injected using a split ratio of 20:1. The quadrupole MS conditions were: electron ionization source; electron energy 70 eV; MS detector temperature set at 230 \({}^{\circ}\)C; the temperature of the transmission line was 280 \({}^{\circ}\)C; the mass range was 35-500 amu. Qualitative and quantitative evaluation of volatile compounds was performed as follows. The volatile components were characterized by mass spectrometry, retention index (RI) was compared [29], and the MS results were searched using the NIST14.0 database, while compounds were characterized based on MS matches and structural information, and volatile compounds were identified if the matches were greater than 800. The actual RI values of the target compounds were compared to the standard RI values, and the standard RI values were matched to the NIST 14.0 mass spectrometry database. The peak times of the target compounds were matched with those of a series of n-alkanes (C4-C22) and the actual RI values were calculated using the following equation. \[RI=\left(n+\frac{t^{\prime}_{r}(x)-t^{\prime}_{r}(n)}{t^{\prime}_{r}(n+1)-t^{ \prime}_{r}(n)}\right)\times 100 \tag{1}\]  
where \(n\) is the carbon number; \(t^{\prime}(x)\) is the retention time of the compound retained between carbon number \(n\) and \(n+1\) n-alkanes; \(t^{\prime}(n)\) is the retention time of n-alkanes with carbon number \(n\); \(t^{\prime}(n+1)\) is the retention time of n-alkanes with carbon number \(n+1\). The results of the method with internal standards are relatively stable and the data are accurate. In this study, internal standards were added to semi-quantify the aromatic compounds in green huajiao.