Influence of the Culture System and Harvest Time on the Specialized Metabolite Composition of Rocket Salad (Eruca sativa) Leaves

Abstract

Eruca sativa is a leafy vegetable widely consumed fresh in salads and recognized for the presence of bioactive compounds, such as glucosinolates (GLS) and flavonols. This plant is traditionally cultivated in soils but adapts well to soilless cultures, such as hydroponics and aquaponics. However, despite the good results in the literature on E. sativa cultivation in soilless systems, the influence of the culture systems and harvest time on the specialized metabolite-based chemical composition of E. sativa leaves is not entirely understood. Based on the above, this study aimed to evaluate the specialized metabolite composition of three different cultivation types, i.e., using soil (SCS), nutrient film technique (NFT)-based hydroponic (HCS), and aquaponic (ACS) culture systems, along three growing cycles, and collected at two commercial harvest times, i.e., 21 days after transplanting (DAT) to get early plant material, namely “baby leaf”, and 42 DAT as the traditional harvest time. The chemical composition was obtained by liquid chromatography coupled with mass spectrometry (LC-MS), and multivariate statistics supported the analysis of the whole dataset. The SCS was characterized to promote an important accumulation of two antioxidant flavonols, i.e., (kaempferol and isorhamnetin diglucopyranosides) in young leaves (21 DAT). The hydroponically-grown plants exhibited a smaller number of various compounds. The ACS-cultivated leaves accumulated indole-containing glucosinolates and a marker associated with harvest time, spirobrassinin, a cruciferous oxindoline phytoalexin. These findings constitute the first report of those compounds relevantly accumulated by the effect of soilless cultures and a starting point for further studies related to the metabolite regulation of E. sativa under hydroponics and aquaponics.