Drying Characteristics of Roselle (Hibiscus Sabdariffa) Calyces Under Low-Temperature and – Relative Humidity Atmosphere

Abstract Roselle (Hibiscus sabdariffa ) offers nutritional and medicinal benefits for human life. To preserve its quality and shelf life, the post-harvest measures should be taken appropriately. Drying is the common method to preserve its shelf life and occasionally its quality. The current study is concerned with the experimental investigation of the drying characteristics of Roselle calyces at low temperature and low relative humidity conditions. A household refrigerator was utilized to produce low temperature and low humidity environment. The experiment included two different drying loadings; the first used 550 g of fresh calyces, while the second used 275 g. During drying, the air temperature and relative humidity in the drying chamber fluctuated in a saw-like manner and their profiles mirrored each other; whenever the temperature increased, then the relative humidity decreased, excepting that after the first point of inflection both temperature and relative humidity decreased. The air temperature ran between 1°C to 4°C. At the first stage, the relative humidity dropped to 30%, then increased, and fluctuated between 50% and 60%. The drying loading did not affect the air temperature and relative humidity profiles, excepting the extent to which the curves ceased. The moisture loss took place fairly slow at first and faster afterwards. The drying rates did not reveal a constant-rate period. Both drying loadings showed similar drying rate profile, except that for higher drying loading, the profile shifts to the higher moisture content.