Original research articleProbing the free-radical scavenging activity of the extract, the major glucosinolate and isothiocyanate of Eruca sativa Mill. and Lepidium densiflorum Schrad. seeds

•Lepidium densiflorum seed extract has scavenging activity towards DPPH and OH.•L. densiflorum extract contains sinalbin which was not a good antioxidant.•4-hydroxybenzyl isothiocyanate was a better scavenger than sinalbin.•Glucoerucin was a better DPPH scavenger than erucin.•The glucosinolates and their isothiocyanates investigated are weak scavengers.

Sinalbin (SNB) and 4-hydroxybenzyl isothiocyanate (4-HBITC) were isolated from Lepidium densiflorum Schrad. seeds, while glucoerucin (GER) and erucin (ER) from Eruca sativa Mill. seeds. Free-radical scavenging assays (2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals (OH)) were used. The amount of plant extract required to scavenge 50% of the DPPH radicals (SC50) was 0.35 ± 0.053 mg mL−1 for L. densiflorum and 0.55 ± 0.067 mg mL−1 for E. sativa extract. The latter, however, was a better scavenger towards OH (3.4 ± 0.38 mg mL−1 for L. densiflorum vs. 1.0 ± 0.081 mg mL−1 for E. sativa). 4-HBITC was more active towards DPPH and just as active as ER towards OH. As expected, 4-HBITC was a better scavenger than SNB towards DPPH and OH. On the contrary, GER was found to be more efficient at scavenging DPPH than ER while their activities towards OH were the same. Overall, the compounds were not very efficient antioxidants.