Optimization of ethanol extraction of antioxidative phenolic compounds from torrefied oak wood (Quercus serrata) using response surface methodology

A torrefaction treatment process followed by ethanol extraction was applied for extracting antioxidant components from oak wood. Response surface methodology (RSM) was applied to optimize the ethanol extraction conditions of antioxidant compounds from torrefied oak wood (severity factor Ro = 4.23). Response values were assessed such as total polyphenol content, total flavonoid content, and DPPH radical scavenging activity. Optimal extraction conditions were found as follows: ethanol concentration 69.15 %, extraction temperature 71.60 degrees C and processing time 70.15 min for total polyphenol content; ethanol concentration 66.93 %, extraction temperature 69.52 degrees C and time 66.09 min for total flavonoids content; ethanol concentration 68.18 %, extraction temperature 51.77 degrees C and time 74.22 min for DPPH radical scavenging activity. The experimental values agreed with those predicted within a 95 % confidence interval indicating the suitability of RSM in optimizing the ethanol extraction of antioxidant compounds from the torrefied oak wood. However, no significant correlation was found between antioxidant activity (DPPH), neither with total polyphenol content nor with total flavonoid content.