Application of response surface methodology to optimize the drying condition of black tea using superheated steam dryer

Abstract

Drying conditions of black tea using superheated steam (SHS) was optimized based on central composite design (CCD) of response surface methodology (RSM). The effects of independent variables (temperature and time) towards the total phenolic content (TPC), scavenging free radical ability, ferric-reducing antioxidant power assay and sensory attributes (infusion colour, aroma, flavour and astringency) were analysed using regression polynomial equations. Analysis of variance (ANOVA) showed that quadratic model fitted the experimental design well, with a p-value less than 0.05 and highest coefficient of 0.9474. The optimum drying conditions were achieved at 166.74°C and 21.2 minutes where the experimental values were in accordance with predicted values, with percentage errors (PE) less than 10%. Temperature (140°C – 180°C) was concluded to have most significant effect and showed a positive direction in most responses. This effect definitely able to support the application of a SHS dryer for the quality production (antioxidant and sensory properties) of black tea.