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

Abstract

Drying conditions of black tea using superheated steam (SHS) were optimized based on a 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, avour and astringency) were analysed using regression polynomial equations. Analysis of variance (ANOVA) showed that a quadratic model tted the experimental design well, with a p-value less than 0.05 and a highest coefficient of 0.9474. The optimum drying conditions were achieved at 166.7°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 the most signicant effect and showed a positive direction in most responses. This effect was denitely able to support the application of a SHS dryer for the quality production (antioxidant and sensory properties) of black tea.