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

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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 Keywords: of 4.4 kDa. Determination of basic physicochemical parameters using elemental antioxidant activity analysis, functional group analysis, UV-Vis-and FTIR-spectroscopy of OS-M fermented leaves indicated that the isolated polymer was similar to typical melanoidins. Experimental Lamiaceae data show that aromatic fragments dominate the OS-M structure, which also contains melanoidin a small amount of aliphatic fragments. Investigation into the antioxidant activity of Orthosiphon stamineus Benth 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.