Characterisation and free radical scavenging activities of novel red pigment from Osmanthus fragrans’ seeds

A novel red pigment (RP) was isolated from Osmanthus fragrans  ’ seeds. The optimised experimental parameters of extraction obtained with a four-factor at three-level orthogonal array experimental design L9(34)L9(34) were ethanol concentration, temperature, pH and extraction time as 90%, 78 °C, 2.5 and 40 min, respectively. A yield of 34.6 ± 2.2 g/100 g was obtained under optimised conditions. The red pigment directly from O. fragrans’ seeds can be dissolved in alkaline, acidic waters solutions and hydrophilic organic solvents in common use. The colour of a water solution of RP changed with pH. RP was stable to heat in the temperature range of 25–100 °C. Physical and chemical properties of RP revealed that the red pigment was also stable in the presence of Na2SO3, NaCl, amino acid, organic acid, sugar, starch or metal-ions (such as Ca2+, Cu2+, Fe3+, Zn2+, Al3+, Mg2+ and Na+), but was bleached by strong oxidants (KMnO4, K2Cr2O7 and NaOCl). Subsequently, free radical scavenging activities of RP were assessed using 2,2′-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals using a new resonance scattering spectral method. RP showed an excellent DPPH radical scavenging activity and was superior to butylated hydroxytoluene (BHT), and exhibited quite a strong concentration-dependent inhibition of hydroxyl radical at low concentrations compared with ascorbic acid and quercetin. When the concentration of RP was 0.03 μg/ml, the scavenging percentage of hydroxyl radical reached 92.3%. Salidroside was isolated as an active principle.