Huang Tzou-Chi, Teng Chia-Shih, Chang Jia-Lin, Chuang Hui-Su, Ho Chi-Tang, Wu Mei-Li
Department of Food Science, National Pingtung University of Science & Technology, 912, Pingtung, Taiwan.
J Agric Food Chem. 2008 Aug 27;56(16):7399-404. doi: 10.1021/jf8011739. Epub 2008 Aug 5.
2-Acetyl-1-pyrroline (2-AP) was identified as the major flavor compound in aromatic rice varieties Tainung 71 and 72. In order to understand the mechanism of 2-AP biosynthesis in aromatic rice, we studied the formation of putative precursors, Delta(1)-pyrroline-5-carboxylic acid and methylglyoxal. The endogenous Delta(1)-pyrroline-5-carboxylic acid contents of Tainung 71 and 72 calli reached 191 to 276%, compared to nonaromatic rice Tainung 67. In addition, calli of Tainung 71 and 72 contained 1.30- and 1.36-fold, respectively, higher methylglyoxal levels than that of Tainung 67. Specific enzyme activities of Delta(1)-pyrroline-5-carboxylic acid-synthetic enzyme including Delta(1)-pyrolline-5-carboxylic acid synthetase (P5CS) and ornithine aminotransferase (OAT) increased significantly in aromatic rice varieties. The expression levels of P5CS1 and P5CS2 genes were found to be significantly higher in aromatic rice than nonaromatic rice. Results of a tracer experiment with (15)N-labeled glutamic acid revealed that the nitrogen atom of 2-acetyl-1-pyrroline was derived from glutamic acid. Upregulation of P5CS in aromatic rice Tainung 72 may contribute to the increase of Delta(1)-pyrroline-5-carboxylic acid level and thus leads to the accumulation of an extra amount of 2-acetyl-1-pyrroline.
2-乙酰基-1-吡咯啉（2-AP）被鉴定为香稻品种台农71和72中的主要风味化合物。为了了解香稻中2-AP生物合成的机制，我们研究了假定前体δ¹-吡咯啉-5-羧酸和甲基乙二醛的形成。与非香稻品种台农67相比，台农71和72愈伤组织中的内源性δ¹-吡咯啉-5-羧酸含量达到了191%至276%。此外，台农71和72的愈伤组织中甲基乙二醛水平分别比台农67高1.30倍和1.36倍。包括δ¹-吡咯啉-5-羧酸合成酶（P5CS）和鸟氨酸转氨酶（OAT）在内的δ¹-吡咯啉-5-羧酸合成酶的比酶活性在香稻品种中显著增加。发现香稻中P5CS1和P5CS2基因的表达水平显著高于非香稻。用¹⁵N标记的谷氨酸进行的示踪实验结果表明，2-乙酰基-1-吡咯啉的氮原子来源于谷氨酸。香稻品种台农72中P5CS的上调可能有助于δ¹-吡咯啉-5-羧酸水平的增加，从而导致额外量的2-乙酰基-1-吡咯啉的积累。
