Phenolic compounds, antioxidant activity and ultrastructural study from Protea hybrid 'Susara'

Abstract

In the present study we investigated the chemical composition and the phenolic contents of the ethanolic extract from aerial parts of Protea hybrid ‘Susara’, its antioxidant activity and also the structure and ultrastructure of the leaves and stems by light microscopy (LM) and transmission electron microscopy (TEM). Phytochemical research led to the isolation of twelve compounds including: (6-ethoxy-3,5-dihydroxy-4-oxotetrahydro-2H-pyran-2-yl)methyl 4-hydroxybenzoate (1), 4-ethoxy-2,3-dihydroxy-4-oxobutyl 4-hydroxybenzoate (3), 2-ethoxy-4-(hydroxymethyl)phenol (4) and 1,5-anhydro-d-glucitol (5). Moreover, fourteen phenolic compounds were identified and quantified by RP-HPLC, and the predominant was catechin, followed by gallic and syringic acids. Compound 4 showed the highest radical scavenging activity (98%) with a half-time (t1/2) of 10 s. In TEM, the phenolic compounds were osmiophilic, appearing within the cell lumen of different tissues as isolated droplets of different sizes and fine granular material. Aerial parts presented thick cuticles and heavily lignified tissues with strong reinforcements of sclerenchyma, all indicating scleromorphic features. Our finding suggested that some agriculture waste biomass could be converted into high-added value products with a potential use within the food preservation, pharmaceutical, cosmetic and therapeutic industries.