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Improved x-ray spectrometric method for determining glucosinolates

A. Pinkerton1, P.J. Randall1and R.J. Mailer2

1 CSIRO Division of Plant Industry, G.P.O. Box 1600, Canberra, A.C.T. 2601
2
NSW Agriculture, Agricultural Research Institute, Wagga Wagga, NSW 2650

Glucosinolates are the most detrimental components in oilseed rape; their breakdown products in the high protein meal after oil extraction can adversely affect animal growth. The Australian oilseeds industry has adopted the Canola standard, i.e. <30 pmol/g of four particular glucosinolates in meal. A rapid method for determining glucosinolates in seed and meal of rapeseed and other oilseed brassicas is essential for screening cultivars in breeding programs and for analysing batches delivered for crushing.

Methods

A recently developed X-ray fluorescence spectrometric (XRFS) method ( I) for determining oxidised S (S6+) and carbon bonded S (Sc) in plant material utilizes the small SK wavelength shift with change in chemical bonding (oxidation number). A glucosinolate molecule contains two S atoms, one S6+ and one Sc (Fig. I). Protein contains only Sc atoms. Analysis for S6+ provides an estimate of glucosinolate content (Fig. I ).

Figure 1. Principal S fractions in rapeseed.

Figure 2. Linear relationship between S6+ in rapeseed and total glucosinolates determined by glucose release (2).

Results and discussion

S6+ is highly linearly correlated with glucosinolate contents determined by chemical Methods (Fig. 2). Errors from inclusion of sulfate are small because sulfate, a small fraction of total S. is correlated with glucosinolates. The S6+ method is superior to an existing XRFS method (2) which uses total S because protein S. a large fraction of total S. is not correlated with glucosinolates.

References

4. Pinkerton. A.. Randall. P.J. and Norrish. K. 1991. Commun. Soil Sci. Plant Anal. 20. 1557-1574.

5. Mailer. R. and Wratten. N. 1985. Aust. J. Exp. Agric. 25. 932-8.

6. Wathelet. J.P., Wagstaffe, P.J. and Boenke. A. 1991. Report CD-NA-13339-EN-C. Office for Official Publications of the European Communities, Luxembourg.

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