Near-IR Spectroscopy Analyzes Sesame Seeds

Daniel S. Burgess

One of the oldest known condiments, sesame seeds are a good source of dietary fiber, vitamins and minerals, including manganese and copper. Recently, sesame oil received attention as a source of polyunsaturated fats and of the antioxidants sesamin, sesamolin, sesaminol triglucoside and sesaminol diglucoside, which act to lower cholesterol and blood pressure and which may offer other health benefits.

Sesame seeds contain unique antioxidants that may offer health benefits. To better enable the identification and breeding of strains with the highest levels of these compounds, researchers are investigating the suitability of near-IR reflectance spectroscopy for the analysis of sesame seeds.

To enable sesame producers to breed strains with high levels of these beneficial compounds, scientists at Mokpo National University in Muan and at Kangwon National University in Samcheok, both in South Korea, are evaluating the suitability of near-IR spectroscopy for the nondestructive analysis of the seeds. Although further work will be necessary to develop a library of calibration models, their initial experiments suggest that near-IR spectroscopy can replace the destructive and labor-intensive high-performance liquid chromatography technique for this application.

Using a near-IR scanning monochromator from Foss NIRSystems Inc. of Laurel, Md., the researchers collected reflectance spectra between 400 and 2500 nm at a resolution of 2 nm from 63 4-g samples of intact seeds in a standard ring cup. It took approximately 1.5 minutes to collect a spectrum from a sample. In contrast, high-performance liquid chromatography, which they also employed in the experiments for reference, required days of sample preparation time and measurement runs of 20 minutes.

To test the calibration models they obtained from the spectra using various regression methods, they collected spectra from an additional 30 samples of sesame seeds. They determined that analysis for sesamin and sesamolin is best performed using data collected at 1600 to 1700 nm, for sesaminol triglucoside at 400 to 2500 nm, and for sesaminol diglucoside, at 1100 to 2500 nm.

The investigators note that the viability of near-IR spectroscopy for this application relies on having a calibration data set collected from specimens that are similar to those under analysis. Accordingly, it will be necessary to acquire spectra from sesame seeds cultivated in a variety of conditions, subjected to different drying and storage methods and harvested at various times of the growing season.

Journal of Agricultural and Food Chemistry, June 28, 2006, pp. 4544-4550.