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Drying Characteristics of Ginger Rhizome (zingiber Officinale)

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

M A Hoque
Bangladeh Agricultural Research Institute, Gazipur, Bangladesh

M A Hossain
Bangladeh Agricultural Research Institute, Gazipur, Bangladesh

M Borhan Uddin
Department of Food Technology, Bangladesh Agricultural University, Mymemnsingh 2202, Bangladesh

Abstract/ Executive Summary:

This paper presents the drying characteristics of ginger rhizome under blanched and nonblanched conditions using hybrid solar dryer and mechanical tray dryer at three temperature levels. The drying rate increases with the increase in drying air temperature and blanching also increases the drying rate. The drying rate depends on shape and size of the ginger rhizomes. The highest drying rate was found for sliced samples of ginger rhizome followed by splitted and whole root samples. Five thin layer drying models were fitted to the experimental data of blanched and sliced ginger rhizomes. The Page equation was found to be the best followed by Midilli, Kucuk & Yapar (2002). The agreement between the predicted and experimental results was excellent. Colour of ginger rhizomes were slightly changed after drying. Lightness of ginger rhizomes decreased with an increase in drying temperature for all samples except sliced and blanched samples. The colour of the dried sliced and blanched ginger rhizome for different drying air temperatures was almost same. For drying of ginger rhizome, it must sliced and blanched and dried either at 60 ⁰C or 70 ⁰C in a mechanical tray dryer for better quality dried products.

Keywords: Ginger rhizome, Hybrid solar dryer, Tray dryer, Lanching, Lhin layer drying model, Colour change.

Location: BAU, Mymensingh

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity: Ginger

Objectives:

To determine the drying characteristics of ginger rhizome using solar hybrid and tray dryer.
To determine the optimum drying air temperature, develop models of drying kinetics and also assess the quality attributes of dried ginger rhizome in terms of color.

Methodology:

The hybrid dryer installed at BARI was used for drying of ginger rhizome at 50 ⁰C (Hossain & Hoque, 2008) and the tray dryer at BARI laboratory was used for drying of ginger rhizome at 60 ⁰C and 70 ⁰C and three drying experiments were conducted. Fresh ginger rhizomes were collected from local market of Gazipur district in Bangladesh. The ginger rhizomes were processed in three different sizes (whole, splitted and sliced). Three samples of each of the different shape and size of the product were water blanched and another three samples were non-blanched. Fresh ginger rhizomes were dried in three forms- whole, longitudinally splitted and sliced. Whole fresh rhizomes were cut longitudinally to make just equal two parts by knives. Slicing was done with a mechanical slicer in 4 mm in thickness measured by a vernire slide calipers. Three samples of all three forms were blanched at 80 ⁰C for 5 min utes. The initial moisture content of the ginger rhizome was determined by oven method drying at 105 ⁰C for 24 hr (Park, Vohnikova, & Brod, 2002). The dryer basically consists of a solar collector and a drying unit. The dimensions of the flat plate concentrating solar collector were 2.3 m long, 1.6 m wide and 0.5 m high. The transparent cover of the collector was 4 mm thick clear glass. Black painted corrugated iron sheet about 200 mm below the glass cover was used as an absorber plate. To increase the efficiency of the solar collector, flat type reflector made of glass mirror was added at top of the solar collector. The dimensions of the reflector were the same as those of the solar collector so that it could be used as a reflector in day time and as a cover in night time or in adverse weather. This reflector had adjustable angles that could be changed according to the change of the sun’s angle during the day to collect higher amount of sun rays that fall down on the solar collector. In addition, the collector was placed on 4 legs with 140 mm wheel to turn the solar collector horizontally and change its direction according to the change of the sun’s angle. The solar collector was insulated by 50 mm thick polystyrene. A centrifugal blower operated by a 0.75 kW, 220 V electric motor was connected at one side of the collector to draw the atmospheric air in the collector and push out the heated air into the dryer at a desired air velocity. Air flow was controlled by a variac connected with the electric motor. For auxiliary heating, two electric heaters (2 kW´2= 4 kW) were installed at the entry of the collector. A temperature controller was set to maintain constant temperature inside the dryer. The length and width of the solar dryer were same as the collector (2.30 m ×1.60 m). It was located directly under the solar collector and 200 mm under the absorber plate. It was divided into 4 parts with equal dimensions. In each of the parts there were 2 trays for drying. This allows the usage of 8 drying trays in the drying unit. The drying air was passed across the ginger placed in thin layers on 8 horizontally stacked trays and arranged in two vertical columns. Each tray was made of wooden frame and plastic net with dimensions of 1040 mm × 780 mm. The drying air was heated up in the solar collector and passed to the drying chamber. The drying air from the solar collector was passed through a curved passage downward, then again turned into the drying unit to flow over and under all the drying trays and then exhausted through an outlet. The temperature in the dryer was maintained constant at 50 ± 1⁰C using temperature controller and adjusting airflow by a variac.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 1.42 m ´ 0.64 m ´ 0.86 m. Inner dimensions of the chamber are 0.80 m ´ 0.50 m ´ 0.60 m. There were arrangements for fixing five trays. Heated air was passed in over the trays through fourteen holes and passed out with same numbers of holes. Air was circulated over the electric heater installed at the bottom of the dryer with a fan sucking fresh air from the right side of the dryer. There was an arrangement to control the velocity of the air by reducing or increasing the opening of the holes. Sensors were used to detect the temperature level. When the temperature is higher than the desired temperature, the heating system is off and the reverse is true when the temperature is below the desired temperature. The ginger rhizome as a whole, splitted and sliced (4 mm) were dried under blanched and nonblanched conditions at 50⁰C using solar hybrid dryer and at 60⁰C and 70⁰C 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 inside the dryer. Drying was started usually at 09:00 am and continued until it reached the final moisture content. Ambient temperature and temperature inside the dryer temperature was measured with a digital thermometer (K202, Voltcraft digital thermometer, Germany) connected with k type thermocouples. Solar radiation was measured with a Lux meter (LX-9626, China) during the day time. Velocity of drying air was measured with a thermo-anemometer (AM-3848, China). Weight losses of the samples in the solar dryer were recorded during the drying period at two hours of interval with an electronic balance (EK-200g, Max 200 ± 0.01g). 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. Thin layer drying equations and expressions for the drying parameters as a function of drying conditions are required for simulation of the drying systems (Bala, 1997). Three general approaches for thin layer drying are the development of (1) empirical equations, (2) theoretical equations and (3) semi-theoretical equations. Theoretical approach concerns either the diffusion equation or simultaneous heat and mass transfer equations. Semi-theoretical approach concerns approximated theoretical equations. The main justification of the empirical approach is a satisfactory fit to all experimental data. The details of the development of thin layer drying models and expressions of the drying parameters are given in Bala (1997). This study considers empirical and semi-theoretical thin layer drying equations. The colour of fresh and dried ginger rhizome samples were measured by a chromameter (CR- 400, Minolta Co. Ltd., Japan) in CIE (Commission Internationale l’Eclairage) Lab chromaticity coordinates. L*, a* and b* represent black to white (0 to100), green to red (-ve* to +ve) and from blue to yellow (-ve* to +ve) colours respectively. Out of five available colour systems, the L*a*b* (Krokida, Tsami & Maroulis, 1998; Lozano & Ibarz, 1997; Maskan, 2001) and L*C*ho (Zhang, Baerdemaeker & Schrevens, 2003) systems were selected because these are the most widely used systems for evaluation of the colour of dried food materials. The instrument was standardized each time with a white ceramic plate. Three readings were taken at each place on the surface of samples and then the mean values of L*, a* and b* were averaged. The different colour parameters were calculated using the following equations (Lopez Camelo & Gomez, 2004).

Source of Information: Proceedings of the 5th CIGR Section VI International Symposium on Food Processing,Monitoring Technology in Bioprocesses and Food Quality Management, Potsdam, Germany, 31 August - 02 September 2009

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Drying characteristics of ginger rhizomes of different shape and size at three temperature levels of 50, 60 and 70 ⁰C under blanched and non-blanched conditions were investigated. The drying rate increases with the increase in drying air temperature and hence the drying time decreases with increase in drying temperature.The rate of increase of drying rate was relative low at low temperature. Blanching increases the drying rate and there is a significant difference between the drying curves for blanched and non blanched samples. The drying rate depends on shape and size of the ginger rhizomes. The highest drying rate was found for sliced samples of ginger rhizome followed by splitted and whole root samples. Five thin layer drying models were fitted to the experimental data of blanched and sliced ginger rhizomes. The Page equation was found to be the best followed by Midilli, Kucuk & Yapar (2002). The agreement between the predicted and experimental results was excellent. Colour of ginger rhizomes in combination of L* (from black to white), a* (from green to red) and b* (from blue to yellow) were slightly changed after drying. Lightness of ginger rhizomes decreased with an increase in drying temperature for all samples except sliced and blanched samples. The colour of the dried sliced and blanched ginger rhizome for different drying air temperatures was almost same. For drying of ginger rhizome, it must sliced and blanched and dried either at 60 ⁰C or 70 ⁰C in a mechanical tray dryer for better quality dried products.

Knowledge Management: Report/Proceedings