Development of Analytical Methods for Profiling Rice Aroma Volatiles, 2013



Project Leader

Susan Ebeler, professor, Dept. of Viticulture and Enology, UC Davis

Florence Negre-Zakharov, associate professor, Dept. of Plant Sciences, UC Davis

The goal of this new project is to develop analytical methods for profiling rice aroma volatiles that could be used in rice breeding programs to identify desirable characteristics.

An important volatile compound—2-acetyl-1-pyrroline (2AP)—is associated with a “popcorn-like” aroma in certain rice varieties. The objective of 2013 research was to develop a sensitive, high-throughput analytical method to analyze 2AP in single grains of rice and plant material such as rice leaves.

Based on discussions with scientists at the Rice Experiment Station (RES), researchers focused on whole rice kernels. Analyses were performed before cooking to determine initial amounts of 2AP.  (Future work may focus on the amount of 2AP formed as a result of thermal processing.)

Approximately 50 freshly milled rice samples (varieties and crosses) from the RES were analyzed for 2AP using gas chromatography combined with mass spectrometry. Several different solid phase microextraction (SPME) fiber phases were evaluated for sample preparation in order to obtain maximum response to 2AP. Extraction temperature and time conditions were also optimized. This method required minimal sample preparation and can be used with single rice kernels or larger samples.

The 2AP concentrations were generally consistent with what was expected, based on the breeding crosses and on prior analyses at RES. Importantly, differences in 2AP levels were observed among samples from the same variety planted in different fields and headrow plantings from different locations. Some varieties and crosses also appear to be more variable within a sample than others.

Significant variability among metabolites between biological replicates can be common in fruits and vegetables but has not been well-characterized in rice.