Volatiles recovered in novel, diverse and uncharacterized long-grain rice varieties: Research Note

Authors: Beaulieu, John; Grimm, Casey; OBANDO-ULLAO, JAVIER - Costa Rican Institute For Research And Education On Nutrition And Health(INCIENSA); McClung, Anna

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2022
Publication Date: 6/17/2022
Citation: Beaulieu, J.C., Grimm, C.C., Obando-Ulloa, J.M. and McClung, A.M., Volatiles recovered in novel, diverse and uncharacterized rice varieties. Cereal Chemistry. https://doi.org/10.1002/cche.10579
DOI: https://doi.org/10.1002/cche.10579

Interpretive Summary: Whole rice and varieties with colorful bran offer consumers proven health-benefits. Two USDA long-grain rice varieties, and two others varieties that offer health-promoting capacity due to their unique germplasm were selected to study. These varieties have been characterized agronomically and/or with regard to phenolics and anthocyanin compounds but, not for volatiles. Besides the most important volatile in aromatic rice, 2-acetyl-1-pyrroline, there are well over 100 other aroma compounds in the literature across a wide range of aromatic and/or colorful bran rice varieties. Researchers have begun working with several novel and/or new rice varieties to develop value-added beverages, flours, freeze dried powders and health-promoting foods. We are interested in exploring the endogenous rice volatiles immediately after de-hulling, to differentiating possible volatile contributions from freshly prepared whole kernels, bran and flours. Four previously uncharacterized varieties (Rondo, Cahokia, Scarlett Tiara) were chosen to obtain volatile baselines that will be used to explore changes resulting from rice germination and processing during value-added product development. To the best of our knowledge, this is the first GC-MS volatiles report in Rondo, Cahokia, Scarlett and Tiara. Of the three colored-bran varieties, the purple rice Tiara delivered some of the highest compound levels for key aroma-impact volatiles known in rice, especially those varieties with colorful bran. For example, heptanal, 2-acetyl-1-pyrroline, benzaldehyde, guaiacol (2-methoxy phenol) and total compounds were significantly higher in Tiara, and benzothiazole had the significantly highest levels in Tiara and IAC600 compared to Scarlett, and the brown varieties. Cahokia high-protein rice delivered a surprisingly high volatile load, however, several compounds fell into classes that indicate oxidation and/or sensory issues if concentrations are excessive. Cahokia displayed the highest significant volatile compound levels reported in the analysis for hexanal, 2-heptanone, 1-heptanol, 1-octen-3-ol, octanal, (E)-2-octenal, 1-octanol, nonanal and total volatiles. Several other compounds were tentatively identified that might be of interest since they have pleasant fragrances. A more in-depth analysis and compound confirmation with standards is underway, to ultimately deliver a more comprehensive review of these data and trends.

Technical Abstract: Background and objectives. There is interest in developing value added rice based products with enhanced nutritional value, however organoleptic properties are critical for product acceptance. Five diverse rice varieties, four of which were previously uncharacterized, were evaluated for volatile compounds in whole grain, milled rice, bran, and flour to determine compound differences that may affect flavor. Findings. This is the first report of GC-MS volatiles recovered in Rondo (used for beverages and flour), Cahokia (a high protein brown rice), and two new pigmented bran varieties: Scarlett (red) and Tiara (purple) rice. Conclusion. Tiara delivered some of the highest levels for five key aroma-impact volatiles known in rice (heptanal, 2-AP, 2-pentyl furan, benzaldehyde, guaiacol), especially regarding those varieties with pigmented bran. Cahokia also delivered a high volatile load of several compounds that indicate possible postharvest shipping/handling oxidation in the paddy rice. Several compounds were identified that are associated with pleasant fragrances in other commodities. Significance and novelty. Five diverse rice varieties developed for specialty culinary and nutritional markets were characterized for 19 volatile compounds in whole grain and milled rice and their associated bran and flour. These volatiles may impact organoleptic properties influencing utilization of these varieties for future value added product development.