Objective The study was conducted to understand the change characteristics of aroma components of aromatic cultivars at various developmental stages, with an emphasis on the exploration of the dynamic changes of aroma 2 acetyl-1-pyrroline (2AP) in different stages of grains.

Method The aroma compounds in two superior aromatic rice cultivars Meixiangzhan 2 (MXZ) and Xiangyaxiangzhan (XYXZ) of Guangdong Province were identified by headspace solid phase microextraction (HS-SPME) in combination with gas chromatography-mass spectrometer (GC–MS) method. Identification of aroma components in 11 samples cpllected from different developmental stages was conducted, including leaves at jointing stage (S1), spikelets at booting stage (S2), branches at booting stage (S3), milky grains (S4), glume of 10 days after flowering (DAF) (S5), dough grains (S6), glume of 20 DAF (S7), mature grains (S8), glume of 30 DAF (S9), brown rice (S10) and polished rice (S11).

Result A total of 63 volatile compounds (belonging to 7 chemical classes) in two rice cultivars were identified. There were about 35-40 compounds in most of samples, of which 14 compounds were detected in all samples. There were two rice cultivars with the most species and richest content of aroma compounds in the booting stage. In MXZ S3 stage, 43 aroma compounds were detected, of which 19 showed highest accumulation. Similarly, 42 aroma compounds were detected in XYXZ S2, of which 16 showed highest content. By contrast, the aroma compounds in S5 with the least species were identified, and 28 and 27 compounds were detected in the two rice cultivars, respectively. The 2AP was detected in all samples except for glumes. 2AP content was highest in leaves (100-120 ng/g), and the content decreased gradually with the maturity of grains. Significantly, the 2AP content of XYXZ in all grain stages was higher than that in MXZ. There were about 40 aroma compounds in S10 and S11. The contents of hydrocarbon, aldehyde and alcohol were higher than those of other classes. Further, the aroma compounds content in polished rice was lower than that in brown rice. 1, 2, 4-Trimethylbenzene and isophorone were only detected in the MXZ polished rice, while benzeneacetaldehyde, 1-octene-3-ol and dihydro-5-pentyl-2(3h)-furanone were specifically detected in XYXZ polished rice, indicating that these compounds contribute to the characteristic flavor of each aromatic rice.

Conclusion The aroma volatile profiles were similar between MXZ and XYXZ at various developmental stages. The booting stage was a key developmental stage where the aroma compounds were synthesized. The content of 2AP decreased gradually with the maturity of grains. The content of 2AP in all MXZ samples in various stages was lower than that in XYXZ. However, the content of most components including hydrocarbon, aldehyde, alcohol, ketone and ester in the polished rice were higher than that in XYXZ.