| Kelp ( Laminariaja ponica ) is a kind of nutritious sea vegetable. Kelp produced in Fujian Province was used as the material in this research was dried and then pulverized through different methods. The optimal parameters of dehydration pulverization was selected through orthogonal experiments. Furthermore, its physicochemical properties and application depengding on the theoretical foundation were also studied.Firstly, kelp was dried through the methods of hot-air drying, micro-wave drying, vacuum microwave drying and vacuum freeze drying respectively and the ingredients change of kelp and the energy consumption of every method are measurated. The yields of dried kelp powder through above-mentioned methods were compared. The results indicated that the progress of hot-air drying, microwave drying and vacuum micro-wave drying all could be divided into three periods, namely accelerating period, constant speed period and speed-reducing period. Whereas, when kelp was pre-frozen before vacuum freeze drying, its drying period was further divided into sublimation drying period and analytic drying period, and the content of calcium, magnesium, selenium and iodine in dried kelp was relatively higher than those through the other three methods. The energy and time consumption of microwave drying and vacuum microwave drying is less, but the powder yield of or above 200 meshes was comparatively lower than those through other methods. The vacuum freeze drying method consumed more time and energy but the highest yield of powder of or above 200 meshes was given. To be a Compromise between time and energy consumption and powder yield, the method of hot-air drying was proved to be the optimum method.In the second place, single-factor experiments, with factors including amount of roughly pulverized kelp powder (500g, 625g, 750g, 875g, 1000g), wind speed of ultra-mizer (14 Hz, 23 Hz, 32 Hz, 41 Hz, 50 Hz), rotating speed of ultra-mizer (10 Hz, 17 Hz, 24 Hz, 31 Hz, 38 Hz), and water content of kelp powder (5%, 9%, 13%, 17%, 21%), were done in this research. Then orthogonal experiments, with factors including wind speed (28 Hz, 32 Hz, 36 Hz), rotating speed (36 Hz, 38 Hz, 40 Hz), amount of roughly pulverized kelp powder, were also done. The two groups of experiments mentioned above showed that the optimal amount of kelp powder above 80 meshes, optimal wind speed and optimal rotating speed are 690g, 32 Hz and 40 Hz respectively. Under this condition, the yield rates of ultra-micro kelp powder of or above 200 meshes of kelp dried through vacuum freeze drying, hot-air drying, microwave drying and vacuum microwave drying were 74.78%, 71.34%, 46.10% and 42.06% respectively.Thirdly, the physicochemical properties of ultra-micro kelp powder were studied. The structure of kelp powder was observed with electron microscope and its angle of repose, angle of slip, wettability, solubility and stability of its turbid liquid with water, and expansibility are measurated. The results show that the best method of kelp processing is vacuum freeze drying, which is followed by hot-air drying, and the indexes of microwave drying and vacuum microwave drying are various.Finally, kelp powder processed through different drying methods and of different grain diameters were applied to different uses. Through applying kelp powder into the processing of bread, the ranking of influencing factors (from the greatest to the slightest) of kelp bread was proved to be: yeast powder, amount of kelp powder, grain diameter of kelp powder, the drying method of kelp powder. And the kelp bread with 1.9% of yeast powder and 2% of kelp powder was proved to be the best on condition that the kelp powder should be above 200 meshes and should be dried through vacuum freeze drying. Ultramicro kelp powder also can be added to other foods and the application of ultramicro kelp powder in food processing has a bright market prospect. Through analysis, processing and application, conclusion is made that the kelp powder of or above 200 meshes enjoys the widest application. |
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