First isolation of tryptophan from edible lotus (Nelumbo nucifera Gaertn) rhizomes and demonstration of its antioxidant effects

Abstract

Various vegetables were investigated for antioxidant activities in two assays, namely, inhibition of lysis of erythrocytes induced by peroxyl radicals and inhibition of lipid peroxidation. The lotus (Nelumbo nucifera Gaertn) rhizome showed the strongest antioxidant activity in both assays. The crude extract (L) of lotus rhizome was chromatographed on a macroporous adsorption resin named NKA. The resulting three fractions were designated L1, L2 and L3, respectively. L2 showed the highest antioxidant activity and was further fractionated by Sephadex LH-20 chromatography. Eight fractions were obtained and named from L2a to L2h, respectively. L2c showed the strongest activity in inhibiting hemolysis of erythrocytes and was further purified by high-performance liquid chromatography. L2c-3 was identified as tryptophan. Its inhibitory concentration of 50% (IC₅₀) value in inhibiting hemolysis of erythrocytes was 156.3 μg/ml (i.e. 765.4 μM). This is the first report on isolation of tryptophan from the aqueous extract of lotus rhizome and demonstration of their antioxidant activities.

Keywords::

• Tryptophan
• antioxidant
• Nelumbo nucifera Gaertn
• hemolysis

Declaration of interest: The authors thank support of this project by funds from National Natural Science Foundation (grant number 30970021), the Chinese Ministry of Health (grant number 2008ZX10001-002) and the National Key Scientific Program of China (grant number 2008ZX09401-05). The authors declare no conflicts of interest.