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Drying Characteristics of Basoka Leaves (adhatada Vasica)

M A Hoque
Scientific Officer
Machinery Repair and Maintenance Division, Bangladesh Agricultural Research Institute, Gazipur.

B K Bala
Professor
Department of Farm Power and machinery, Bangladesh Agricultural University, Mymemnsingh-2202

M A Hossain
Senior Scientific Officer
Farm Machinery and Post Harvest Process Engineering Division, Bangladesh Agricultural Research Institute, Gazipur

Abstract/ Executive Summary:

This study presents the drying characteristics of basoka leaves under blanched and non-blanched conditions using hybrid solar dryer and mechanical tray dryer at three temperature levels (40, 50 and 60°C). The drying rate increases with the increase in drying air temperature as well as blanching also increases the drying rate. Moisture contents of basoka leaves were 3.85% (wb) and 4.83% (wb) for blanching and non blanching samples after 9 hours and 14 hours of drying at 40°C while the initial moisture content was 80.60% (wb). For drying at 50°C it took 7 hours to reduce moisture content of blanched leaves to 3.36% (wb) but for non-blanched samples it took 10 hours to reduce moisture content to 4.66% (wb) from equal initial moisture content 80.37% (wb). Drying at 60°C in a mechanical dryer with blanching and without blanching reduced the moisture content from 77% (wb) to final moisture content of 3.26% and 4.28% (wb) after 6 hours and 8 hours of drying respectively. The intensity of green (-a*) colour of blanched basoka leaves was significantly higher than that of the non-blanched leaves. Five thin layer drying models have been fitted to the experimental data of blanched basoka leaves. The Page equation was found to be the best followed by Midilli et al. (2002) model. The agreement between the predicted and experimental results was excellent.

Keywords: Drying characteristics, Basoka leaves, Balanched and non balanched condition

Location: BARI

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Basok (Malabar nut)

Objectives:

To determine the optimum drying air temperature and develops models of drying kinetics and also assesses the quality attributes of dried basoka leaves in terms of color.

Methodology:

The hybrid dryer installed at BARI was used for drying of basoka leaves at 40 and 50°C and the tray dryer at BARI laboratory was used for drying of basoka leaves at 60°C. Fresh basoka leaves were collected from local villages of gazipur sadar upzilla. Three samples were water blanched and another three samples were non-blanched. Three samgles of basoka leaves were blanched at 80 e for 3 minutes. The initial moisture content of the basoka leaves was determined by oven method drying at 105°C for 24h. The hybrid dryer basically consists of a concentrating type solar collector and a drying unit. The dimensions of the flat plate concentrating solar collector were 2.3m long, 1.6m wide and 0.5m high. The mechanical tray dryer consists of a drying chamber, heater, electric blower etc. The overall dimensions of the drying chamber of the mechanical tray dryer are 1.42m x 0.64m x 0.86m. Inner dimensions of the chamber are 0.80m x 0.50m x 0.60m. The leaves of basoka were dried under blanched and non-blanched conditions at 40 and 50°C using solar hybrid dryer and at 60°C using tray dryer. Before starting an experimental run, the whole apparatus was operated for at least one hour to stabilize the air temperature and air velocity in the dryer. Drying was started usually at 09:00 am and continued until it reached the final moisture content (about 3 to 5%, wb). Ambient temperature and temperature inside the dryer temperature was measured with a digital thermometer connected with k type thermocouples. Solar radiation was measured with a Lux meter during the day time. Velocity of drying air was measured with a thermo-anemometer. Weight losses of the samples in the solar dryer were recorded during the drying period at one hour of interval with an electronic balance. After completion of drying, the dried samples were collected, cooled in a desiccator to the ambient temperature and then sealed it in the plastic bags. Mathematical models for thin-layer drying of leaves of basoka under blanched conditions were developed by using direct least square method between moisture ratio MR) and drying time (t). Moisture ratio was defined. Five commonly used thin layer equations were selected to fit the experimental data of drying of blanched basoka leaves by the direct least square method using SPSS 1l.5. The constant final moisture contents were considered as the equilibrium moisture contents of the samples.

Source of Information: JOURNAL OF AGRICULTURAL ENGINEERING, Vol-36/AE, pp. 01-12, JUNE 2009, ISSN:0379-4318.

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Blanching increases the drying rate of basoka leaves. The drying rate increased with the drying air temperature. Moisture contents of basoka leaves were 3.85% (wb) and 4.83% (wb) for blanching and non blanching samples after 9 hours and 14 hours of drying at 40°C while the initial moisture content was 80.60% (wb). For drying at 50°C it took 7 hours to reduce moisture content of blanched leaves to 3.36% (wb) but for non-blanched samples it took 10 hours to reduce moisture content to 4.66% (wb) from equal initial moisture content 80.37% (wb). Drying at 60°C in a mechanical dryer with blanching and without blanching reduced the moisture content from 77% (wb) to final moisture content of 3.26% and 4.28% (wb) after 6 hours and 8 hours of drying respectively. Green (-a*) colour of blanched basoka leaves was significantly higher than that of the non-blanched leaves. The lightness increased for blanching and decreased with the increase in drying air temperatures. Hue angle also decreased with the increase in drying air temperatures. This implies that colour change was not significant between 50 and 60°C. The chroma of the dried product was significantly changed due to blanching, but change in chroma due to increase in drying air temperature was insignificant. Five thin layer drying models were fitted to the experimental data of blanched basoka leaves. The Page equation was found to be the best. The agreement between the predicted and experimental results was excellent.

Knowledge Management: Journal