Studies on moisture sorption isotherm and nutritional properties of dried Roselle calyces

Freshly harvested roselle calyces of dark and light red varieties were sundried and oven dried and evaluated for proximate composition and moisture sorption studies. pH of sundried roselle calyces were higher than oven dried roselle calyces. Also, oven dried dark red Roselle calyces was significantly higher in crude protein, fat, dry matter, moisture and ash. Higher values potassium, phosphorus, sodium, magnesium, iron, zinc and calcium were also found in red Roselle calyces. Vitamin C content of oven dried light red Roselle calyces was significantly lower than Vitamin C of other Roselle calyces at p 0.05. Roselle calyces exhibited the typical three stage sigmoidal curve found in most foods Braunaeur-Emett-Teller (BET Type II). There was also a concomitant increase in the equilibrium moisture content (EMC) as relative humidity increased in all roselle calyces irrespective of the temperature regimes. Sun dried roselle calyces gave the highest rate of water absorption unlike oven dried roselle calyces. In conclusion oven drying is the best method to dry freshly harvested roselle calyces, oven dried dark red roselle calyces was high in nutrient composition and all roselle calyces exhibited the typical three stage sigmoidal curve found in most foods Braunaeur-Emett-Teller (BET Type II).