Screening Glucosinolates, Their Hydrolysis Products, and Quinone Reductase Anticancer Activity of the USDA Arugula Germplasm Collection

Rocket or arugula (Eruca sativa Mill.) is common leafy vegetable consumed since ancient times in the Mediterranean region as a vegetable and for its medicinal properties. Arugula contains the phytochemical glucosinolates glucoerucin and glucoraphanin that are precursors of erucin and sulforaphane, isothiocyanates that provide mammalian anticancer bioactivity. Leaf tissue of 41 arugula USDA germplasm accessions were harvested from the greenhouse and assayed for glucosinolate and hydrolysis products concentrations by high performance liquid chromatography and gas chromatography, respectively. Glucoraphanin, glucoerucin, and dimeric glucosativin were the major glucosinolates with concentrations ranging from 0.51–8.66, 0.58–7.32, and 3.16–17.45 µmol/g dry weight, respectively. Concentrations of hydrolysis products of glucoraphanin (sulforaphane) and glucoerucin (erucin) ranged from 0.18–6.45 and 0.28–4.30 µmol/g dry weight, respectively. There were significant positive correlations between glucoraphanin and sulforaphane (r² = 0.82) as well as between glucoerucin and erucin (r² = 0.79). Nitrile forms of hydrolysis products were not detected by GC-MS and GC-FID, suggesting that there was no epithiospecifier protein activity in arugula. Quinone reductase (QR) activity as an anticancer biomarker was measured on leaf samples of 41 arugula germplasm accessions. There was more than 2.3-fold QR inducing activity difference between lowest and highest accessions. This information will be useful for the identification and development of arugula cultivars with improved health promoting properties.