Study Of The Microwave-assisted Foam-mat Drying For Blackcurrant Pulp

As an abundant nutrition and pleasent flavor berry, fresh blackcurrant berry and its product are paid great attention by the domestic and overseas consumers for its products. The powder from the dehydration of blackcurrant berry can be as the food additive directly and drink after seasoning process. Microwave-assisted foam mat drying (MFMD) method combined advantages of foam mat drying and microwave drying mode, which manufactures the high quality blackcurrant berry powder. However, little researche was reported on MFMD equipment and its application for the dehydration of blackcurrant berry.This study aim to design a set of microwave-assisted foam mat drying system for the drying of blackcurrant berry, and to realize pipelining drying blackcurrant berry by using MFMD method, which may provid important theoretical basis for subsequent industrialisation production.The paper were studied as the following aspects:1. A blackcurrant berry pulping and foaming machine was designed and manufactured, which could be applied pre-treated provided foamed materials before microwave drying process.Its main structure include material tank, stirring apparatus, material conveying cube and baffle.Part entities establish, the whole structure assemble and interference check were conducted by three-dimensional design software CATIA. The material mechanics and finite element analysis were used to stress analysis and strength check the key components, these provided reliable guarantee for manufacture and operation of the machine.2. To meet the requirements of mechanical motion, both stirring apparatus motor control system and material conveying apparatus control system were designed. Stirring apparatus motor provided power for stirring apparatus using a frequency conversion, which meet differential speed requirements. Control system for the material conveying apparatus controls the motion of stepper motor using micro control unit (MCU) to realize the motion of the stepper motor with the positive and negative motion direction and distance, to control turning angle in the process of motion and to adjust the motor speed. This control system provides the precision of material conveyin.3. Microwave-assisted foam mat drying experiment for blackcurrant pulp were conducted by designed pulping and foaming machine fixed existed microwave dehydrator. A response surface analysis method with three factors and three levels was applied to analyze and optimize the drying parameters, in terms of browning of color, anthocyanin content and moisture content (d.b.) for final moisture content of materials, and the corresponding regression model was established .The results show that the sequence of the effect of various factors on browning of color from high to low is drying time>initial microwave intensity> thickness of material layer. The sequence of the effect of various factors on colormoisture content (d.b.) is initial microwave intensity>drying time> thickness of material layer. The sequence of the effect of various factors on the anthocyanin content is initial microwave intensity>drying time>thickness of material layer.The reasonable drying parameters were obtained as follows: the initial microwave intensity of 10 w/g, the drying time of 8 min, and the equivalent thickness of foamed pulp of 6 mm. An experiment verfied the validation of optimal parameter.4. According to reasonable drying parameters obtained from the experimental results, a continuous microwave dehydrator was designed, which is composed of the microwave system, resonator, transmission system and the fan. A microwave-assisted foam-mat drying system was developed, which combinates three processes including pulping, foaming machine and continuous microwave dryer for the drying of blackcurrant pulp.