Comparative effects of noble metal nanoparticles on glucosinolates, phenolic compounds and antioxidant activity in kale (Brassica oleracea var. acephala) in vitro cultures.

Kale (Brassica oleracea var. acephala) shoot cultures were supplemented with Au, Pt, Ag or Cu nanoparticles (NPs; 5-15 ppm; ≤5 nm) to modulate their phytochemical composition. ICP-MS, UHPLC-HRMS, LC-DAD and four antioxidant assays were applied to evaluate metabolic outcomes. PtNPs produced the strongest and most comprehensive enhancements, raising total glucosinolates (GLS) from 4.06 μmol/g DW (control) to 9.75 μmol/g DW (10 ppm) and markedly increasing key indolic GLS, including glucobrassicin (5.10 μmol/g DW; 10 ppm PtNPs), 4-methoxyglucobrassicin (1.59 μmol/g DW; 15 ppm PtNPs) and neoglucobrassicin (2.67 μmol/g DW; 10 ppm PtNPs). Selected phenolic compounds showed the strongest increases under PtNPs treatment, particularly rosmarinic acid, reaching 58.49 mg/100 g DW (15 ppm PtNPs), and caffeic acid, reaching 26.04 mg/100 g DW (10 ppm PtNPs). Consistently, PtNPs yielded the highest antioxidant activity across FRAP, DPPH, CUPRAC, and ABTS. MTT and LDH assays indicated no overt cytotoxicity of most NPs-enriched extracts, although selected condition-dependent effects were observed.