Results and discussion
Drying analysis
During drying at 35 °C, the heat pump dryer was able to reduce the RH to 27 ± 2%. The RH measured during hot air drying at 45 °C was 60 ± 5%. Variation in moisture content with time during air drying of Pandanus leaves at drying air temperature of 35 °C and 27% RH and 45 °C with 60% RH is shown in Fig. 1. The corresponding values of standard deviation for each data point have been shown through vertical bars. From the plot of moisture content against drying time, it is clearly evident that drying time was less in case of hot air drying at 45 °C. The total time required for drying at 35 °C was 900 min and at 45 °C was 540 min to reduce the moisture content from 382.28% db to about 5% db. The reduction of total drying time with increase in temperature may be due to increase in vapour pressure within the product, which resulted in faster migration of moisture to the product surface. The plots in Fig. 1 followed the general trend of drying curves as reported for many food materials (Ahmed and Shivhare 2001; Davinder and Shashi 2005; Pal et al. 2008). At the higher temperature, the drying curve exhibited a steeper slope, thus exhibiting an increase in drying rate.