The thymol method for glucosinolate determination

This paper details experiments aimed at optimising the conditions for the determination of glucosinolates in rapeseed (Brassica napus L) using the colorimetric thymol procedure. Glucose could not be substituted for sinigrin when preparing a standard curve for glucosinolate determination unless a correction factor was employed. The value of this factor was found to depend on the concentration of sulphuric acid. Although the coloured complexes formed between thymol and either glucose or sinigrin were found to be unstable at 100°C, the sinigrin/ glucose colour ratio remained relatively constant for incubation times from 40 to 60 min. It was found necessary to increase the amount of thymol present to a final value of 0.23% to ensure complete reaction of glucosinolates. The revised method can be employed successfully for the analysis of glucosinolates in both seed and meal.