Antioxidant Activity and Stability of Nanocapsules of Red Ginger (Etlingera flexuosa) Endemic to Central Sulawesi

Abstract

Nanoencapsulation is a technique used to maintain the active compounds’ stability against environmental stressors. Etlingera flexuosa, an endemic ginger found in Central Sulawesi, is being explored for its potential as a herbal medicine by formulating its extract into nanocapsules. The objectives of this research are to evaluate the antioxidant activity, physicochemical characteristics, and stability of E. flexuosa ginger nanocapsules under varying conditions of temperature, pH, and sodium chloride (NaCl) concentrations. The rhizome, stem, and leaf of E. flexuosa ginger were extracted using ethanol. The nanoencapsulation employed κ-carrageenan as the coating matrix, with extract-to-matrix ratios of 1:1, 1:2, 1:3, 2:1, and 3:1. Antioxidant activity was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and the nanocapsules’ stability was evaluated using UV-Vis spectrophotometry. 
The results showed that the best antioxidant activity (IC₅₀) of the nanocapsules was obtained at an extract-to-matrix ratio of 1:2. The IC₅₀ values of rhizome, stem, and leaf extract of E. flexuosa ginger, respectively, were 53.73 µg/mL, 80.36 µg/mL, and 102.10 µg/mL. After nanoencapsulation at an extract-to-matrix ratio of 1:2, the IC₅₀ values of rhizome-NPs, stem-NPs, and leaf-NPs were 43.22 µg/mL, 77.38 µg/mL, and 94.61 µg/mL, respectively. Particle size analysis revealed that the nanocapsules derived from three parts of E. flexuosa ginger had sizes below 1000 nm. The zeta potential (ζ) values for rhizome-NPs, stem-NPs, and leaf-NPs were -6.4 mV, -6.9 mV, and -8.1 mV, respectively. The nanoencapsulation effectively preserved the bioactive compounds’ stability from the rhizome, stem, and leaf of E. flexuosa ginger under varying pH, temperature, and NaCl concentrations.