Development and validation of a spectrophotometric method for simple quantification of total glucosinolates in cruciferous vegetables

Given their putative role in chemoprevention, there is an acknowledged need for validated methods for quantification of total glucosinolates in cruciferous vegetables. Based on the ferricyanide reaction with the 1‐thioglucose alkaline degradation product of glucosinolates described by Jezek et al. (J Agric Food Chem 47, 4669), we have developed a more simple and sensitive method for extraction and spectrophotometric quantification of total glucosinolates in various cruciferous vegetables. After shock freezing in liquid nitrogen, lyophilized and ground vegetables are treated with 80% boiling methanol to deactivate myrosinase and extract glucosinolates. Glucosinolates are then eluted through a strong anion exchange extraction cartridge, followed by treatment with 2N NaOH to release 1‐thioglucose. After addition of ferricyanide, absorption is measured at 420 nm and final values are adjusted for interfering compounds. Recovery of a sinigrin internal standard was 80%. The intra‐assay coefficient of variation was 7.9%. Linearity in dose response was observed with both internal standard (R 2 = 0.99) and amount of plant material extracted (R 2 = 0.99). Using sinigrin, the lower limit of detection was 0.1 μm/mL. This straightforward method may serve as an alternative to more time‐consuming and costly chromatographic methods. Support: Healthy Foods, Healthy Lives Institute.