| Hot air coupling microwave (AD&IM) drying was adopted for ginger drying, in the meanwhile intermittent and varied power microwave was used to make microwave more homogeneous. Different pre-treatments (osmotic dehydration, high pressure, carbon dioxide maceration) was combined with AD&IM in order to find out the most suitable, efficient, energy saving and best quality preserved approach for ginger drying. The main results and conclusions are as follows:(1) Hot air drying, infrared drying, freezing drying, microwave drying and AD&IM drying were selected to conduct the comparison of drying energy consumption, drying time and quality preserved of dried ginger slices. The results showed that AD&IM drying played an excellent role in retaining6-gingerol,8-gingerol and10-gingerol content as well as its merits of shorter drying time and lower energy consumption. The extract of ginger dried by AD&IM yields the best scavenging ability of DPPH· and ABTS·.(2) The osmosis effectively inhibited enzymatic browning reactions, and had a good protection for color and phenolic compounds of ginger. Dried samples after constant pressure osmosis and pulsed vacuum osmosis had a better rehydration ratio than samples directly dried by AD&IM. Gingerol, shogaol and zingiberone of dried samples pretreated by pulsed vacuum osmosis were significantly higher than those of ginger directly dried by AD&IM. Volatiles of fresh ginger were more similar to those of dried samples with pulsed vacuum osmosis, which suggested that volatile components of dried gingers could be preserved the when pulsed vacuum osmosis was applied.(3) Dried gingers after500MPa high-pressure pretreatment yielded the best scavenging capability of DPPH-and ABTS-as well as Fe3+reducing ability, significantly higher than samples without high pressure processing. Dried ginger with blanching pretreatment ran the second place while dried samples with freeze combing high pressure treatment turned out to be much weaker in terms of above abilities. The drying rate of ginger after high pressure pretreatment was significantly increased, the drying time of dried samples with freeze combing100MPa,500MPa, blanching and freeze pretreatments were shorten by30%、20%、25%and10%, respectively, compared with dried samples without pretreatments. The fresh samples had more similar volatile components with dried samples pretreated by freeze combining with250MPa and100MPa.(4) A new environmental friendly pretreatment was studied, namely Carbonica Maceration (CM). Carbon dioxide can change the permeability of the cell and trigger the anaerobic respiration, which had positive effect on dynamics of AD&IM drying and quality of dried gingers.CM pretreatments can significantly reduced the drying time.The drying time of ginger pretreated by CM2(0.2MPa,40℃,10h) was reduced by35%.In the meanwhile, CM pretreatment significantly improved the content of gingerol and shogaol of dried ginger.The highest gingerol content was found in CM4(0.2MPa,30℃,10h) pretreated samples and its6-gingerol,8-gingerol,10-gingerol and6-shogaol content were2.49,1.45,1.45and1.36times, respectively, of AD&IM dried samples. Dried gingers with CM pretreatment had much smaller colour change with fresh samples, so CM had very good protection for the color of dried samples.(5) Based on the Lambert law of microwave energy absorption and the second Fick law of mass transfer, one-dimensional planar mathematical models were established to predict the moisture and temperature distribution of ginger during hot air coupling with microwave drying.The relative deviations of models were within10%, suggesting models can well simulate the actual AD&IM drying process of ginger. The models can provide effective means for process optimization and automatic control for AD&IM in production application. |
PDF Full Text Request