Glucosinolate content and isothiocyanate evolution - Two measures of the biofumigation potential of plants

A total of 570 lyophilised Brassica root and shoot tissue samples were hydr olyzed, and the liberated isothiocyanates (ITCs) were analyzed by gas chrom atography-flame photometric detection (GC-FPD). Glucosinolates (GSLs) were extracted from samples of the same tissues and analyzed by highperformance liquid chromatography (HPLC). The concentrations of six GSLs/ITCs (2-propen yl, 3-butyl, 4-pentenyl, benzyl, 4-methylthiobutyl, and 2-phenylethyl) as d etermined by the two techniques were compared. In 79% of the samples, the c oncentration of GSLs in the tissues was greater than that of the ITCs relea sed on hydrolysis. Several possible reasons for the difference are proposed , including the effect of tissue storage time, hydrolysis of GSLs may be le ss efficient than the GSL extraction procedure, or some of the ITCs formed reacted with plant proteins and amino acids in the sample and were therefor e not detected in the extract. GSL concentration in plant tissues is used t o estimate the biofumigation potential of the plant tissue, whereas the act ual biofumigation effect is thought to be due to the ITCs formed by hydroly sis of the plant-based GSLs. The variation between ITC and GSL values there fore has implications for the assessment of the biofumigation potential of the plant tissue.