Characterization of St. John's wort (Hypericum perforatum L.) and the impact of filtration process on bioactive extracts incorporated into carbohydrate-based hydrogels

Hypericum perforatum L. (HPL) is also called as St. John's wort and is traditionally used as a herbal tea and food supplement because of its excellent bioactive properties. One of the main objective of the present study was to investigate the effect of an additional filtration process on the properties of final HPL extract. Physicochemical studies of crude and filtrate extracts were performed by Fourier-transform infrared spectroscopy, UV-vis spectrometry, and gas chromatography with mass spectroscopy. Filtration efficiency was evaluated by dynamic light scattering at 20 degrees C and 37 degrees C. Determined hydrodynamic diameters of the HPL particles were 180 and 189 nm, respectively, after filtration. Bioactivity tests were performed with four bacterial strains from Pseudomonas genus. The effect on bacterial membrane permeability based on the size of extract particles was also determined. The HPL crude and filtrated extracts were then incorporated into three hydrogel matrices: agar-agar, alginate, and apple's pectin. Low-field nuclear magnetic resonance (LF-NMR) and water activity tests were performed to study the biopolymer matrix. Texture analysis and L*-a*-b* color tests were performed according to the possible color change of HPL extract on the biopolymer matrix. Additional filtration processes are preferable to obtain nano-sized plant-based structures and might affect on the final extract properties. A detailed structural analysis of raw materials and carbohydrate-based hydrogels are necessary for further evaluation of bioactive properties.