Mechanical Drying of Senna leaves ( Cassia angustifolia )

Senna (Cassia angustifolia) is an important medicinal crop which is being exported from India. The present method of drying the leaves is under sun or shade which results in poor quality product. An attempt was made to dry senna in a forced flow type dryer at different temperatures. Sennoside concentrate which is an important quality aspect of Senna revealed that drying at 45 °C was superior compared to other samples.

is a general practice of drying the harvested leaves by spreading them on the floor, which results in contamination and affects quality.The appearance and leaf quality deteriorate due to the heat developed inside the thick layer while drying.
Improper and delayed drying changes the colour to black, which results in lower price in the market.(THEHINDU, dated 31.8.2006)Hence drying the crop in a mechanical dryer could alleviate the problem to a lesser extent thereby improving the quality for export market.

Raw material
Freshly harvested senna leaves of the variety KKM-1 were used for conducting drying studies.The harvested leaves were obtained from farmer's field.

Forced flow dryer
The dryer consists of a drying chamber, plenum chamber, heating chamber and a blower driven by 2HP motor.Loading and unloading of the material is done through the door provided at the drying chamber.An inspection door is provided at the front of the dryer.The ambient air entering through the blower gets heated up in the heating chamber having 6 kW electric heaters and enters into the plenum chamber.From the plenum chamber the hot enters into the drying chamber where the product is kept for drying.The hot air after absorbing moisture from the product is discharged into the atmosphere through the exhaust provided above the drying chamber.The overall dimension of the dryer was 900x900x16500 mm.(Fig. 1)

Drying studies
In one set of experiment 5 kg of harvested senna leaves were dried in the dryer at 40° C and in another trial 5 kg of the same was dried at 45°C.Senna leaves were also dried under shade (32±2ºC) for comparison.The initial moisture content of the leaves before drying was estimated by hot air oven method of drying.Weight of the samples were recorded at intermittent intervals during drying and the final moisture content of the sample was estimated based on the final weight achieved at the end of drying.Sennoside concentrate, an important parameter which decides the quality of the sample was estimated analytically.

Statistical analysis
The experimental data was analyzed as per the procedure of one way/ two way classified ANOVA using computer software package"AgRes"

Drying characteristics of senna leaves
Drying studies on senna leaves were conducted at 40 & 45°C temperatures in the forced flow type dryer.The initial moisture content of the   leaves was estimated to be 186 % (d.b) and the leaves were dried to a final moisture of about 5% (d.b).It could be seen from Fig. 2 , it took 2.5 hours to dry senna leaves at 45°C whereas for the same lot at 40°C the drying time was about 4 hours.
For the same lot for shade drying of the leaves it took about 5 days for drying to a final moisture content of 5.9% (d.b) (Fig 3 .)

Effect of drying on the quality of dried senna
The quality of the dried senna leaves were evaluated in terms of its sennoside concentrate (Table 1) Statistical analysis revealed that there was significant difference in the sennoside concentrate at different drying condition.It could be seen that senna dried at 45°C (Fig. 4) showed higher yields (2.69%) in terms of its sennoside concentrate whereas at 40°C it was 2.44 %.However shade dried sample had a low sennoside content of 2.2%.This may be due to the fact that during shade drying, since the sample is spread in layers, heat is formed inside the layers during slow drying which in turn affects the quality of the end product.Improper and delayed drying changes the leaf colour to black, which results in a lower price in the market (Prabhu, 2006)