Total Phenolic Content, Total Flavonoid Content and Radical Scavenging Activity from Zingiber zerumbet Rhizome using Subcritical Water Extraction

Subcritical water extraction (SWE) is an alternative technique that implement water as a solvent. The objective of this work was to compare the efficiency of SWE in temperature range from 100ºC to 180ºC at extraction times ranging from 5 to 25 minutes with an ethanolic soxhlet extraction in terms of total phenolic content (TPC), total flavonoid content (TFC) and radical scavenging activity (RSA) from Zingiber zerumbet.  Results showed the highest TPC were obtained at 180ºC and 25 min (19.88 mg GAE/g dry sample). The TFC is observed to be slightly fluctuated with time at the respective temperature. The RSA reached the maximum of 83.9 % inhibition at 180ºC and 10 minutes of SWE. A direct linear correlation shows the strong correlation were observed between TPC and RSA(R2=0.910) compared to moderate correlation (R2=0.785) perceived in TFC. It shows that using SWE, phenolic content in Zingiber zerumbet more contributed to its radical scavenging activity compared to its flavonoid content. In comparison to soxhlet extraction, SWE process for Zingiber zerumbet extract is favorable for TPC and antioxidant properties. However the values for TFC in general is lower compared to soxhlet extraction. SWE is a potential alternative extraction process that should be further explored.