# Profiling Taste and Aroma Compound Metabolism during Apricot Fruit Development and Ripening
## 2 Results
### Changes in Organic Acids during Fruit Development and Ripening  
As shown in Figure 4a, all organic acids including oxalate, tartrate, quinate, malate, citrate, fumarate and total organic acids mostly increased during the early stages of fruit development (from S1 to S3) and decreased until fruits were full-ripe (from S4 to S5). Oxalate, tartrate, quinate, malate, citrate, and fumarate decreased from 2.07 to 0.07 mg/g FW, from 1.56 to 0.12 mg/g FW, from 33.47 to 2.98 mg/g FW, from 27.72 to 6.44 mg/g FW, from 10.22-3.53 mg/g FW and from 0.03-0.01 mg/g FW, respectively. Quinate, malate and citrate were the predominant organic acids throughout the whole fruit development and ripening period. Oxalate and tartrate were found at lower levels, while trace fumarate was also detected in the fruit of cultivars tested during the whole development period. The content of quinate in HY, YH and LT increased to the peak at the turning stage of fruit development, whereas BX accumulated the largest amount of quinate at stage 2 (S2), then decreased to the lowest point at the full-ripe stage (S5). The level of quinate in DX almost kept deceasing throughout the whole development period. Except for HY, higher level of quinate in pulps were found than in peels. DX had the highest quinate content of all tested cultivars. YC and BX presented significantly lower level of quinate than other cultivars tested. Malate in DX, YC and BX increased to the highest level at stage 2 (S2), and then kept decreasing. Malate in DX and LT reached the highest level at stage 3 (S3) and stage 4 (S4). Higher level of malate in peels of DX, YC and LT were observed than in their  
Figure 3: Sugar content (mg/g fresh weight, FW) and ratio in apricot fruit during development and ripening. (**a**) Changes in soluble sugar content; (**b**) The ratio of individual sugar content to total sugar content. Two capital letters in the middle are the cultivars shown in Table 1. All data are expressed as means \(\pm\) standard error of triplicate samples. pulps. A significantly lower level of malate was found in YC than other cultivars tested. The level of citrate kept increasing until stage 3 (S3) or stage 4 (S4) of fruit development, and then decreased at the full-ripe stage. HY presented the lowest level of citrate than other cultivars tested. Except for YC, oxalate generally decreased throughout the whole development period, and the lowest level of oxalate was found in HY. Significantly higher levels of oxalate were found in pulps than in peels. Tartrate was only detected in YC, LT, BX and DX peels, and the content of tartrate in peels tested increased to the highest level at stage 3 (S3), and then declined. Higher levels of tartrate in peels were observed than in pulps. Total acid had a similar trend to that of quinate. DX had significantly higher organic acids identified than other cultivars. Figure 4: Organic acid content (mg/g FW) and ratio in apricot fruit during development and ripening. (**a**) Changes in organic acids; (**b**) The ratio of individual organic acid content to total organic acids content. Two capital letters in the middle are the cultivars shown in Table 1. All data are expressed as means \(\pm\) standard error of triplicate samples. As for the ratio (Figure 4b), quinate, malate and citrate are the predominant organic acids in apricot regardless of developmental stage. Malate is the first major organic acid in apricot. The ratio of malate in fruit decreased from 71.97% to 34.14% in peels and 69.78% to 21.25% in pulps of cultivars tested, respectively. The ratio of quinate also decreased from 55.03% to 7.09% of total organic acids in peels and from 55.03% to 15.57% in pulps during development and ripening, respectively. However, the ratio of citrate increased significantly from 0% to 36.52% in peels and 0% to 45.98%, respectively. Quinate and malate account for more than 85% of total organic acids at the early stage, they are the major organic acids of fruit tested during early development.