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Drying Kinetics of Ginger Rhizome (zingiber Officinale)

M. A. HOQUE
Scientific Officer
FMP Engineering Division, Bangladeh Agricultural Research Institute (BARI), Gazipur

B. K. BALA
Department of Farm Power and Machinery, Bangladesh Agricultural University (BAU), Mymemnsingh 2202

M. A. HOSSAIN
Senior Scientific Officer
FMP Engineering Division, BARI, Gazipur

M. BORHAN UDDIN
Department of Food Technology and Rural Industries, BAU, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

This paper presents the drying kinetics 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 to predict the moisture content of sliced ginger rhizome in thin layer. The agreement between the predicted and experimental results was excellent. Colour of ginger rhizomes was slightly changed after drying. Lightness of ginger rhizomes decreased with an increase in drying temperature for all samples except sliced and blanched samples. For drying of ginger rhizome, it should be sliced and blanched and dried below 70⁰C for better quality dried products.

Keywords: Ginger rhizome, Hybrid solar dryer, Tray dryer, Blanching, Thin layer drying model, Colour change.

Location: Bangladesh Agricultural Research Institute (BARI)

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Ginger

Objectives:

The purpose of this study is to determine the drying kinetics 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 colour.

Methodology:

The hybrid dryer installed at Bangladesh Agricultural Research Institute (BARI) was used for drying of ginger rhizome at 50 ⁰C (Hossain and Hoque, 2008) and the tray dryer at BARI laboratory was used for drying of ginger rhizome at 60⁰C 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 e.g., whole (60 mm length @ 20 mm dia. finger), splitted (60 mm length @ 20 mm dia finger splitted longitudinally to make two) and sliced (20 mm dia. finger @ 4 mm thickness). Three samples of 100 g each of the different shape and size of the product were water blanched and another three samples were not blanched. Fresh ginger rhizomes were dried in three forms- whole, longitudinally splitted, and sliced. Whole fresh rhizomes were cut longitudinally to make equal two parts by knives. Slicing was done with a mechanical slicer in 4 mm in thickness. Three samples of all three forms were blanched at 80⁰C for 5 minutes (Murad et al., 2004). The initial moisture content of the ginger rhizome was determined by oven method drying at 105⁰C for 24 hours (Park et al., 2002). Comparison of temperature at 50, 60, and 70⁰C were made in this study. Here temperature is factor and there is no effect of method of temperature (whether it is raised by solar, cabinet dryer or other means). It is convenient to raise temperature 50⁰C in solar dryer and 60 and 70⁰C temperature in cabinet dryer. So, solar and cabinet dryer was used to dry ginger at different temperature. Experimental procedure The ginger rhizome as a whole, splitted, and sliced (4 mm) were dried under blanched and non-blanched 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 in the dryer. Drying was started usually at 09:00 am and continued until it reached the final moisture content (about 8 to 9%, wb). 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.

Source of Information: Bangladesh J. Agril. Res. 38(2): 301-319, June 2013, ISSN 0258-7122

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Drying characteristics of ginger rhizomes of different shapes and sizes at three temperature levels of 50, 60, and 70⁰C under blanched and non-blanched conditions were investigated. 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. The moisture content of the whole ginger rhizome remain almost constant during the whole drying period and this is true for either blanched the whole samples or non-blanched the whole samples. The drying rate increased with the drying air temperature. The rate of increase of drying rate was relative low at low temperature. The drying time decreases with increase in drying temperature. Lightness of ginger rhizomes decreased with an increase in drying temperature for all samples except sliced and blanched samples.

Knowledge Management: Journal