Research On Combination Drying Process And Kinetics Of Ginger Slices Using Microwave-hot Air Dehydration

Ginger was the perennial herbaceous plant roots which had rich nutritional valueand specific medicinal value. Ginger was one of the primary spicy vegetables. Freshginger was not easy to storage in room temperature because of water content above90%. Dehydrated ginger was the one of the main ginger products. Traditional dryingmethods were lack of energy conservation and quality assurance. Microwave and hotair combinaton drying was a new technology integrating microwave drying and hot airdrying, which had characteristics of fast drying rate, high quality and environmentalprotection. Combinaton drying using microwave and hot air was become a researchtrend. Microwave and hot air combinaton drying technology and kinetic models forginger slices were studied. Meanwhile effects on quality characteristics of Hot air andmicrowave combinaton drying were studied. Therefore an important recommendationsfor the further development and industrialization of ginger products was offered.1. Hot air-microwave combinaton drying technique was applied and disscussedfor ginger slices. At first, effects of thickness of ginger slice, hot air temperature,moisture content of conversion point, microwave power on content of gingerol wereinvestigated. On the basis of single factor experiments, hot air-microwavecombination drying process were optimized by response surface methodology ofthree-factor three-level, and corresponding regression equation was established.Results showed that optimum drying conditions were as follows: slice thickness of4mm, hot air temperature of67℃, moisture content of conversion point of36%,microwave power of119W. Under these conditions content of gingerol of(2.04±0.031)%was obtained. Relative error between tested and predicted values ofgingerol content was-0.97%, then they were similar basically.2. Microwave-hot air combinaton drying technique was applied and disscussedfor candied ginger slices. At first, effects of microwave power, moisture contentof conversion point, hot air temperature on the content of gingerol were investigated.On the basis of single factor experiments, microwave-hot air combination dryingprocess were optimized by response surface methodology of three-factor three-level,and corresponding regression equation was established. Results showed thatoptimum combination drying conditions were as follows: microwave power of231W, moisture content of conversion point of65%, hot air temperature of61℃. Under theseconditions, content of gingerol of (0.73±0.025)%was obtained, and relative errorbetween tested and predicted values of gingerol content was-2.67%.3. The hot air-microwave combinaton drying kinetics of ginger slices wereinvestigated. Eight commonly used drying mathematical models were selected andused to fit the experimental data of moisture ratio changes with the drying time usingnon-linear regression analysis for establishing a suitable mathematical model thatdescribes the drying of ginger slices. Results showed that the front hot air dryingprocess could be described with Midilli model MR=aexp(-ktn)+bt and the latermicrowave drying process could be described with Two term model MR=aexp(-kt)+(1-a)exp(-kat).4. The microwave-hot air combinaton drying kinetics of candied ginger sliceswere investigated. Eight commonly used drying mathematical models were selectedand used to fit the experimental data of moisture ratio changes with the drying timeusing non-linear regression analysis for establishing a suitable mathematical modelthat describes the drying of candied ginger slices. Results showed that the frontmicrowave drying process could be described with Page model MR=exp(-ktn) and thelater hot air drying process could be described with Midilli model MR=aexp(-ktn)+bt.5. The quality parameters were compared according to the gingerol content,vitamin C content, rehydration ratio, energy consumption, sensory quality andmicrocosmic structure. The results show that gingerol content, vitamin C content,rehydration ratio in ginger slices dehydrated by combining hot air and microwave werehigher than single hot air drying or single microwave drying products. Ginger slices ofsensory evaluation scores from high to low order was hot air and microwavecombinaton drying, microwave drying, hot air drying. Compared with hot air drying,drying time of microwave-hot air combinaton drying and microwave drying werereduced by55.75%,62.01%respectively. Compared with hot air drying, total energyconsumption of microwave-hot air combinaton drying and single microwave dryingwere reduced by59.76%,98.04%respectively. Compared with single hot-air or singlemicrowave drying method, cellular structure of ginger slices dehydrated by combininghot air and microwave were clear and complete.