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vol. 11, nr. 1 (2008)
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Drying kinetics, water activity, shrinkage and texture of walnut kernels
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Adam Figiel1, Agnieszka Kita2
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1 Institute of Agricultural Engineering, Wroc³aw University of Environmental and Life Sciences, ul. Che³mońskiego 37/41, 51-630 Wroc³aw |
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2 Department of Food Storage and Technology, Wroc³aw University of Environmental and Life Sciences, ul. Norwida 25, 53-375 Wroc³aw |
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vol. 11 (2008), nr. 1,
pp. 71-80
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abstract:
Walnut kernels were dehydrated using two drying methods: convective and vacuum-microwave. In the convective method air velocity was 2 m s-1 and temperature 55C. Vacuum-microwave dehydration was performed under pressure changing from 4 to 6 kPa at microwave power of 480W. The decrease in moisture content of walnut kernels dehydrated in convection was described by a two term exponential function, while in vacuum-microwave method by linear function in the first drying period and by an exponential function in the second period. The relationship between the moisture content and water activity for walnut kernels was described using an exponential equation. The study revealed that shrinkage was changing until the moisture content of walnut kernels reached 0.3 kg kg-1 db. It was found that de-creasing moisture content of walnut kernels till 0.46 kg kg-1 db resulted in considerable increase in the breaking force and breaking extension estimated at bending strength test. Further lowering of moisture content caused a decrease in breaking force while the value of breaking extension remained constant. The significant decrease in breaking extension occurred when exceeding 0.14 kg kg-1 db.
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keywords:
walnuts, drying kinetics, water activity, shrinkage, texture
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original in:
English
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