# Profiling Taste and Aroma Compound Metabolism during Apricot Fruit Development and Ripening
## 2 Results  
### Quality Traits of Apricot during Development and Ripening  
Fruits were classified into five different stages (immature green, S1, maturation green, S2; turning, S3; green ripe, S4; and full ripe, S5) and picked according to peel color (Table 1 and Figure 1). Skin color changed dramatically between maturity stages and ripening. The longitudinal and equatorial diameters of cultivars tested varied from 16.25 to 50.85 mm and 20.83 to 49.55 mm during the development and ripening period, respectively (Figure 2a,b), while the weight increased from 2.6 to 54.35 g. Hongyuxing (HY) had the largest two diameters and fruit weight (Figure 2c), which presented the large fruit shape, and Danxing (DX) and Yechengheiyeyxing (YC) were the medium-sized fruit cultivars, Luntaixiaobiaxing (LT) and Baixing (BX) were the small fruit cultivars. The development of fruits tested was characterized by cell enlargement (0-27 or 32 days), rapid enlargement (0-57 or 91 days) and a period of retarded enlargement (74-101 days).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Cultvars**} & \multirow{2}{*}{**Abbreviation**} & \multirow{2}{*}{**Repository No. 1**} & \multicolumn{3}{c}{**Color Character**} & \multicolumn{3}{c}{**DAB 2**} \\ \cline{6-10}  & & & & **No. 1** & & **peel** & **pulp** & **S1** & **S2** & **S3** & **S4** & **S5** \\ \hline
1 & Danxing & DX & XD076 & red & orange & 21 & 32 & 56 & 74 & 82 \\
2 & Hongyuxing & HY & XD117 & red & orange & 21 & 32 & 61 & 74 & 82 \\
3 & Yechengheiyeycing & YC & XD018 & orange & white & 21 & 27 & 61 & 91 & 91 \\
4 & Luntaixiaobiaxing & LT & XD021 & white & light yellow & 21 & 27 & 57 & 65 & 74 \\
5 & Baixing & BX & XD094 & white & white & 21 & 27 & 61 & 88 & 91 \\ \hline \hline \end{tabular}  
* The united national number of cultivars; 2 DAB, Days after blossom.  
\end{table}
Table 1: Apricot cultivars used in the present study and the sampling time for each stage.  
With the development and ripening, the tittatable acid (TA) level decreased to the lowest point (<0.55 mmol L\({}^{-1}\) H\({}^{+}\)) at the full-ripe stage. Ychengheyexing (YC) and Luntaixioabiaxing presented low TA level at ripe stage (<0.4 mmol L\({}^{-1}\) H\({}^{+}\)), they are low acid cultivars (Figure 2d). In contrast, the total soluble solids (TSS) of fruit increased from 6.7 to 20.47 Brix, TSS of all tested cultivars increased rapidly after turning stage (Figure 2e). For almost all cultivars tested, the TSS increased to double the amount of turning stage at the full-ripe stage, and Danxing (DX) had the highest TSS. A similar trend was observed for the \(\sim\)100  
in change was observed in the ratio of TSS/TA (Figure 2f), the index increased slowly from 2.15 to 6.46 during early development period (S1 to S2), and then increased from 5.78 to 17.78 during the middle period (S3 to S4), at last increased rapidly from 17.78 to 49.75 (S4 to S5) during the ripening period.  
Fruit softened rapidly during development and ripening (Figure 2g). The firmness of fruit for all cultivars tested declined from 47.83 to 2.15 N, and the firmness of all fruit tested was less than 6 N at the full-ripe stage. Danxing (DX) had the lowest firmness of the tested cultivars (2.15 N). The levels of ethylene production increased from stage 1 (S1) to stage 4 (S4), then decreased at the stage 5 (S5) (Figure 2h), and an obvious peak of ethylene were observed at the stage 4 (S4) for all tested fruits (8.24-11.55 \(\mathrm{ng\cdot kg^{-1}\cdot s^{-1}}\)).