| China is a country with high production of ginseng, fresh ginseng water content is as high as 75%, is not easy to save. Study on drying technology of fresh ginseng can effectively improve the quality of dried products, and is an important way to improve the international competitiveness of the ginseng. This paper aims to study on combined microwave and far-infrared drying mechanism, fresh ginseng as the research object, to study the effect of drying process parameters on the drying quality (surface color difference, saponin content, surface shrinkage rate) and drying efficiency (drying time)., optimizing the parameters of drying, provide theoretical and technical guidance for drying ginseng processing. The subject of this paper comes from the Liaoning Province, scientific research fund project-"Drying Characteristic of Combined Microwave and Far-infrared Drying(20141056)’", research contents and achievements included:(1) Experimental study on microwave drying of ginseng slices. Through the effect of different microwave drying time on ginseng slices drying quality (surface color difference, saponin content and surface shrinkage rate), with drying time increased from 90 s to 150 s, slice surface color difference from 2.65 to 4.09, saponin content decreased from 0.14 mgml-1 reduced to 0.025 mgml-1, surface shrinkage rate increased from 5.3%to 25.83%. At the same time, the edge of the slice was severely deformed, so the microwave drying time should not be more than 150 s, and at this moment the water content of ginseng slices was 50%.(2) Experimental study on far-infrared drying of ginseng slices. In the study the slice thickness and drying time were as test factors, slice drying quality (surface color, saponin content, surface shrinkage) and drying efficiency (drying time) were as test indexes. The study included full factorial experiment. Results showed that with increasing of slice thickness from 1 mm to 4 mm, the slice and drying efficiency (drying time), surface color and surface shrinkage rate were generally showing a decreasing trend and saponin content showed increasing trend; with increasing of drying temperature from 50℃ to 65℃, drying efficiency (drying time), surface color and surface shrinkage rate were generally showing a rising trend and saponin content showed decreasing trend.(3) Study on the single factor test of combined microwave and far-infrared. Moisture content of combined microwave and far-infrared drying conversion point (conversion moisture content), slice thickness and far-infrared drying temperature as experiment factors, drying quality (surface color, saponin content and surface shrinkage rate) and drying efficiency (drying time) as test indexes, The single factor test was carried out and the variance of the test results was analyzed. The results showed that the conversion moisture content, slice thickness and far-infrared drying temperature had significant effect on the test indexes, and determined the range of various experimental factors:conversion water content 50-65%, slice thickness 1-4 mm, far-infrared drying temperature 50-65℃.(4) Orthogonal experiment study on combined microwave and far-infrared drying of ginseng slice. Conversion moisture content, slice thickness, and far-infrared drying temperature as experiment factors, drying quality (surface color, saponin content and surface shrinkage rate) and drying efficiency (drying time) as test indexes were studied in the orthogonal test. The results showed that the conversion moisture content, slice thickness and far-infrared drying temperature had significant influence on the test indexed, based on the experimental analysis of the regression equation, the influence sequence of experimental factors on drying efficiency (drying time) was:slice thickness> far-infrared drying temperature> conversion moisture content; the influence sequence on surface color was:slice thickness> far-infrared drying temperature> conversion moisture content; the influence sequence on ginsenoside content was:far-infrared drying temperature> slice thickness> conversion water content; the influence sequence on surface shrinkage rate was:slice thickness> far-infrared drying temperature> conversion water content.(5) Optimization and verification of combined microwave and far-infrared drying process parameters of ginseng slice. Through establishment of mathematical model, response curved face was used to analyse interaction of double factors, using multi-objective nonlinear regression theory and method, first guaranteed ginseng slice drying quality (surface color, saponin content and surface shrinkage rate), followed by consideration of under the premise of the drying efficiency (drying time), the optimal combination of process parameters of combined microwave and far-infrared drying was:conversion water content 65%, slice thickness 3 mm, far-infrared drying temperature 54℃. |
