香稻不同发育时期香味物质的变化分析

Analysis on the Changes of Aroma Compounds in Aromatic Rice at Various Developmental Stages

【目的】掌握香稻整个生长发育过程中香味物质成分的变化特性,重点揭示特征香味物质2-乙酰-1-吡咯啉(2AP)在不同时期籽粒中的变化规律。【方法】采用顶空固相微萃取(HS-SPME)结合气相色谱-质谱技术(GC-MS),以美香占2号和象牙香占两个广东优质丝苗米为研究对象,分别采集拔节期叶片,孕穗期颖花,孕穗期枝梗,花后10、20、30 d籽粒,花后10、20、30 d颖壳,糙米和精米等不同时期的11份样品进行香味物质鉴定。【结果】两个香稻品种共鉴定出7类,63种香味物质,多数样品中香味物质数量为35~40种,其中14种化合物在所有样品中均被检出。两个品种在孕穗期香味物质种类最多、含量最丰富:美香占2号孕穗期枝梗中含43种香味物质,其中19个化合物含量达峰值;象牙香占孕穗期颖花中含42种香味物质,其中16种化合物含量达峰值。花后10 d颖壳中含香味物质种类最少,分别为28、27种。2AP在除颖壳外的其他组织中均被检出,在叶片中含量最高,达100~120 ng/g;随着籽粒成熟2AP含量呈下降趋势,美香占2号各时期籽粒中2AP含量均低于象牙香占。糙米和精米中约含40种香味物质,烃类、醛类和醇类含量较高,精米中多数香味物质含量低于糙米。1,2,4-三甲基苯、异佛尔酮只在美香占2号精米中被检出,而苯乙醛、1-辛烯-3-醇和γ-壬内酯在象牙香占精米中被特异检出,这些香味物质可能对两种米饭特征风味的塑造起重要作用。【结论】两个香稻品种在生长过程中香味物质变化特性相似,孕穗期是香味物质积累的关键时期,随着籽粒成熟2AP含量呈下降趋势,美香占2号各时期样品中2AP含量均低于象牙香占,但其精米中烃类、醛类、醇类、酮类和酯类等多数化合物含量均高于象牙香占。

【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.