Physicochemical characteristics and antioxidant activity of melanoidin pigment from the fermented leaves of Orthosiphon stamineus

Abstract

The melanoidin pigment (OS-M) was isolated from fermented leaves of Orthosiphon stamineus Benth. (Lamiaceae), with a 0.37% yield (from dry plant weight), and characterised. OS-M is a phenolic polymer with a molecular weight of 4.4 kDa. Determination of basic physicochemical parameters using elemental analysis, functional group analysis, UV-Vis- and FTIR-spectroscopy of OS-M indicated that the isolated polymer was similar to typical melanoidins. Experimental data show that aromatic fragments dominate the OS-M structure, which also contains a small amount of aliphatic fragments. Investigation into the antioxidant activity of OS-M under in vitro conditions demonstrated that O. stamineus melanoidin has a scavenging effect against free radicals (DPPH•, ABTS•+, O2•-) and NO molecules, inactivates molecules of H2O2, chelates Fe2+-ions and oxidises NADH.