Drying is a well-known preservation method that uses to extent the shelf life of food materials during storage. In herbal industry, the drying is conducted by using several methods. It is believed that drying methods could affect the herbs physical and chemical properties. In this project, the effects of different drying methods on colour changes, rehydration ratio and bioactive constituent of C. nutans herb were investigated. The herb was dried under sunlight, shade, vacuum oven, and microwave. Results showed that the dried leaves have better retention of TPC and higher antioxidant activity as compared to the fresh leaves. Vacuum oven dried samples showed the highest antioxidant activity and significantly high in TPC. Besides, vacuum and under shade dried herbal leaves had no significant effect on the colour changes. Moreover, leaves dried under vacuum oven was also observed to exert the highest rehydration ratio due to less cell breakdown during drying. Therefore, vacuum drying has greater performance in term of retaining colour, less microstructure changes and greater TPC and antioxidant activity. It could be suggested that by adding vacuum to other drying methods may able to enhance the herbal quality.

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, flavour and astringency) were analysed using regression polynomial equations. Analysis of variance (ANOVA) showed that a quadratic model fitted 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 o C and 21.2 minutes where the experimental values were in accordance with predicted values, with percentage errors (PE) less than 10%. Temperature (140 o C -180 o C) was concluded to have the most significant effect and showed a positive direction in most responses. This effect was definitely able to support the application of a SHS dryer for the quality production (antioxidant and sensory properties) of black tea.

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.