Title: Volatile profile of aromatic and non-aromatic rice cultivars using SPME/GC-MS Authors
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 10, 2010
Publication Date: February 23, 2010
Citation: Bryant, R.J., Mcclung, A.M. 2010. Volatile profile of aromatic and non-aromatic rice cultivars using SPME/GC-MS. Rice Technical Working Group Meeting Proceedings. CDROM P. 108. Technical Abstract: Rice (Oryza sativa L.) is enjoyed by many people as a staple food because of its flavor and texture. Some cultivars, like scented rice, are preferred over others due to their distinctive aroma and flavor. The volatile profile of rice has been explored by many investigators, some of whom have determined a corresponding aroma using GC/Olfactometry. Although it has been shown that storage conditions can affect the aroma and flavor of rice, little research has been done to determine if aromatic rice cultivars from different genetic backgrounds produce flavor volatiles, other than 2-acetyl-1-pyrroline (2-AP), that would make them more desirable over other cultivars when cooked. It would also be important to see if the volatiles profile changes with time and temperature. In this study, seven aromatic cultivars with different genetic backgrounds: Aromatic se2 (Basmati 370 type); Dellmati (Domsiah or Della type); Dellrose (Della type); IAC 600 (Japan type); Jasmine 85 (Khao Dawk Mali 105 type); JES (Khao Dawk Mali 105 type); and Sierra (Della or Basmati 370 type); and two non-aromatic cultivars (Cocodrie and Wells) were double bagged in Ziploc freezer bags and stored at 30oC, 4oC, and -10oC. Each sample was examined for their volatile profile both before storage and every thirty days thereafter for 3 mo. using solid phase microextraction (SPME) fibers in conjunction with gas chromatography/mass spectrometer (GC-MS). Twenty mg of whole milled rice kernels were placed in a 2ml vial and 20ul of ultra-pure water containing 1ng of 2,4,6-Trimethylpyridine (internal standard) was added. The SPME fiber (1cm 50/30 divinylbenzene/carboxen/polydimethylsolaxane stableflex) was allowed to equilibrate for 18 min. at 80oC and then desorbed in the GC injector for 25s at 260oC. Each compound was identified by the presence of selected ions and their ratio, and comparison of the MS spectra obtained in the full scan mode to reference spectra in the National Institute of Standards and Technology mass spectral database. Eleven aldehydes, 15 alkanes, 10 alkenes, 10 ketones, 19 alcohols, 4 amines, 5 acids, and 19 miscellaneous compounds were identified. Of the 93 volatile compounds identified, 64 had not been previously reported in rice. Differences were found in volatile compounds of aromatic and non-aromatic rice other than 2-acetyl-1-pyrroline (2-AP). Most of the volatile compounds were present in freshly harvested rice and rice following storage with very few new compounds being identified only after storage. Dellrose, an aromatic cultivar, and Cocodrie, a non-aromatic cultivar, had the most complex volatile profiles (over 64 volatiles). Wells had the fewest (51) volatile compounds. Sixteen compounds were found only in aromatic cultivars and some volatiles were found to be unique to specific aromatic cultivars. JES contained more compounds that have the potential for production of off-flavors, whereas, Jasmine 85 and Sierra contained the least. However, no distinctive pattern was observed that would identify a cultivar as being derived from Basmati, Khao Dawk Mali 105 (i.e. jasmine), or other sources of aroma. This study showed that there is a great diversity of volatiles in both aromatic and non-aromatic rice cultivars and, with further research, this may lead to a better understanding of the combination of compounds that gives a cultivar a unique flavor.