Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2005
Publication Date: 10/19/2005
Citation: Lee, J., Finley, J.W., Harnly, J.M. 2005. Effect of selenium fertilizer on free amino acid composition of broccoli (brassica oleracea cv. majestic) determinded by gas chromatography with flame ionization and mass selective detection. Journal of Agricultural and Food Chemistry. 53:9105-9111.
Interpretive Summary: Florets from broccoli (Brassica oleracea) grown of four different levels of selenium fertilized soil were analyzed for their amino acid content. Consumption of selenium has been shown to reduce the risk of some cancers. Selenium enriched broccoli is being considered as a commercial product. Previous results had shown that selenium fertilization did increase the selenium content of the broccoli. In this study, we examined the free amino acids and were looking for selenium containing amino acids. Samples were analyzed using a commercially available kit that allowed rapid extraction and derivatization of the free amino acids for analysis by gas chromatography with flame ionization detection (GC-FID) and gas chromatography with mass spectrometric detection (GC-MS). Compared to the control sample, the broccoli grown on selenium fertilized soil had higher levels of all free amino acids and, thus, total free amino acids. The response of individual amino acids to the different levels of selenium was highly variable. The 8 essential amino acids (not synthesized by the body and therefore absorbed from foods) found in broccoli were also higher with selenium fertilization. No selenium containing free amino acids were detectable. These results demonstrate that fertilization with Se modified the free amino acid content.
Technical Abstract: Selenium-enriched broccoli florets, harvested from plants grown on soil inoculated with 4 levels of sodium selenate, were evaluated for their free amino acid composition using alkylchlorformate derivatization, solid phase extraction, and GC-FID or GC-MS. The selenium-enriched florets contained 0.4 (control), 5.7 (treatment A), 98.6 (treatment B), and 879.2 (treatment C) Ug/g Se (dry weight). Twenty-one free amino acids (genetically encoded and secondary metabolites) were identified in the control and all three treatments. The total free amino acid content of the broccoli florets ranged from 178 mmol/kg (dry weight), for the control, to 479 mmol/kg, for treatment C. Broccoli from treatment C contained the highest level of Se, had the most total free amino acids, and had an extremely high level of glutamine (GLN) when compared to the control and the other two treatments. In general, the smallest addition of Se to the soil (treatment A) induced increased levels of all the detectable amino acids when compared to control, while increased additions of Se (treatments B and C) produced mixed responses. Florets from treatment A contained the most essential amino acid content.