Phytochemical profile and biological activities of Nerium Oleander L. flowers and leaves

This study investigated the phytochemical composition and biological activities of leaves and flowers from seven Nerium oleander L. cultivars grown in Tunisia to evaluate their potential for industrial and crop-related applications. Primary metabolite analysis showed that flowers had a higher accumulation of metabolites than leaves, with the 'Roseum Plenum' (RP) cultivar reaching a peak total soluble sugar concentration of 31.57 µg/ml, dominated by sucrose (19.47 µg/ml). Amino acid profiles were also significantly higher in flowers; glycine peaked at 50.66 µg/ml in 'Villa Romaine' (VRS), while 'RP' flowers showed elevated levels of asparagine (3.17 µg/ml) and glutamine (1.18 µg/ml), suggesting elevated amino acid production and stress resilience. Regarding the secondary metabolome, catechin emerged as the predominant compound, reaching 13.67 µg/ml in 'Petit Salmon' (PS) flowers compared to 6.64 µg/ml in 'R' leaves. Other abundant polyphenols identified across the profiles included caffeic and ferulic acids. In addition, quercetin and quercitrin were identified as the main flavonoids, with particularly high concentrations observed in the 'PS' cultivar. Biological assays demonstrated that floral extracts generally possess superior bioactivity. 'RP' flower extracts exhibited exceptional antimicrobial potency, specifically against Escherichia coli and Salmonella typhimurium, significantly outperforming leaf extracts. Antioxidant tests (DPPH, FRAP, and lipid peroxidation) further confirmed that 'PS' and 'Mont Blanc' (MB) cultivars are the most active. These findings indicate that N. oleander flowers, particularly from the 'Roseum Plenum' and 'Petit Salmon' cultivars, serve as high-value sources of bioactive compounds for the development of natural antioxidants and botanical antimicrobial agents in the industrial and agricultural sectors.