Total phenolic content, total flavonoid content and radical scavenging activity from zingiber zerumbet rhizome using subcritical water extraction

Abstract

Subcritical water extraction (SWE) is an alternative technique implemented water as a solvent. The objective of this work was to extract Zingiber zerumbet rhizome using SWE at a temperature range from 100ºC to 180ºC with duration from 5 to 25 min. The extracts were analysed for total phenolic content (TPC), total flavonoid content (TFC) and radical scavenging activity (RSA). Soxhlet extraction using ethanol was used for a comparison purpose. Results showed the highest TPC and TFC was obtained at 180ºC and 25 min extraction, with the yield of 18.52 mg GAE/gDW and 2.34 mg QE/gDW of rhizome for TPC and TFC, respectively. RSA at peak of 83.9 % inhibition at the condition of 180ºC and 10 min extraction. In comparison to Soxhlet extraction, the extract after SWE gives the highest amount of TPC and RSA. However, the values for TFC are lower as compared to ethanolic extract. Therefore, SWE process for Zingiber zerumbet extract is favourable for higher TPC and RSA. A direct linear correlation between the RSA with the TPC and TFC of the extracts shows that a strong correlation was observed between TPC and the RSA with the R2 obtained was 0.910 as compared to moderate correlation (R2=0.785) perceived in TFC. Thus, it shows higher radical scavenging activity in Zingiber zerumbet was contributed by phenolic content as compared to its flavonoid content. In overall, SWE is a potential alternative extraction process that should be further explored.