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vol. 11, nr. 1 (2008)
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Drying kinetics and antioxidant activity of oregano
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Klaudiusz Jałoszyński1, Adam Figiel1, Aneta Wojdyło2
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1 Institute of Agricultural Engineering, Wrocław University of Environmental and Life Sciences, ul. Chełmońskiego 37/41, 51-630 Wrocław |
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2 Department of Fruits and Vegetables Technology, Wrocław University of Environmental and Life Sciences, ul. Norwida 25, 53-375 Wrocław |
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vol. 11 (2008), nr. 1,
pp. 81-90
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abstract:
Oregano was dehydrated by three methods: freeze drying, convective drying and vacuum-microwave drying (VM). Freeze drying was conducted at temperature of -60C and under pressure of 65 Pa. The temperature of heating plate was 30C. Convective drying was performed at three temperatures: 50, 60 and 70C. Hot air velocity was 1 m s-1. In VM dehydration the pressure in drying chamber was changing from 4 to 6 kPa and three microwave power levels were applied: 240, 360 and 480W. The decrease in moisture content of oregano dehydrated in convection was described by an exponential function, while in VM method by a linear function in the first drying period and by an exponential function in the second period. Moisture content at the critical point which divides drying curves into two periods was about 1.4 kg kg-1dm regardless of the drying temperature used. The study revealed that the increase in drying temperature (convective dehydration) and in microwave power (VM) resulted in decreasing of drying time. Freeze drying was the least destructive method of drying because of the antioxidant activity. The most harmful method was convective drying at temperatures of 60 and 70C. It was observed that higher phenolic content in dried oregano may be reached by reduction of temperature in convective method or by increasing the microwave power in V-M method.
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keywords:
oregano, drying kinetics, antioxidant activity, polyphenols
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original in:
English
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