| Pumpkin pomace, the by-product of the pumpkin juice, is rich in β-carotene and dietfiber. The object of this study was to optimize vacuum microwave drying (VMD) of pumpkinpomace in order to extract β-carotene by supercritical fluid extraction (SFE) technique andoptimize SFE of β-carotene from pumpkin pomace. And also investigate a novel productiontechnology for pumpkin powder.One method for the drying of pumpkin pomace was investigated and selected amongVMD, Freeze Drying, Vacuum Drying, VMD-Fluidized bed combined drying. The samplewas dried until the moisture content reached 5% (dry basis). Drying kinetics curve andretention curve of β-carotene were employed. Results showed that the drying time of VMDcombined with Fluidized-bed drying, which is less than an hour, is much less than that ofFreeze Drying and Vacuum Drying, which is more than 20 hours. And also, the deactivationrate of β-carotene in the VMD and combined drying, which are 7.69%, 12.46% and 9.43%,respectively, is similar like that in Freeze Drying, which is 4.25%. VMD was selected todehydrate the pumpkin pomace.During the VMD, the effects of microwave power level (668.37,446.93,250.14W) andvacuum pressure (8000,6000,4000Pa) on the drying rate and β-carotene degradation wereevaluated .Results showed that the drying rate increased with the increasing of the microwavepower. Higher vacuum pressure increased drying rate with a significant drop of β-carotenecontent. A maximum of 92.31% of β-carotene was remained at 668.37w and 4000Pa.Comparing the three empirical drying models, Page equation, with a γ2 of 0.9763, was used todescribe the microwave vacuum drying rate curves of pumpkin pomace which was muchbetter than the other two models.The orthogonal experiments of three factors and three levels, the temperature of theextractor (45,55,65℃),the pressure of the extraction fluid (2.5,3.0,3.5×106Pa) and addition ofcosolvent (0,5,10%,m/m) were used to determine the optimum extraction condition of β-carotene. A maximum of 88.27% of β-carotene was extracted at 65℃ and 2.5×106Pa withthe addition of 10% ethanol as a cosolvent. Concentration of ethanol and temperature werethe most important factors in increasing extraction yield. There was the relation between thecontent ofβ-carotene and color index a.Drying kinetics curve, deactivation curve of β-carotene, color, texture, rehydrationratio, retention rate of β-carotene during storage of the pumpkin powder dried by VMDwere evaluated and compared with those dried by Freeze Drying, Vacuum Drying,VMD-Fluidized bed combined drying. The comparison showed that the quality of pumpkinpowder dried by the combined drying method was close to that of freeze dried pumpkinpowder and much better than that of conventional vacuum dried ones. And theβ-carotenecontent of pumpkin powder dried by Freeze Drying greatly decreased during the storage.The combined drying, a combination of VMD (30min) and Fluidized-bed drying was selectedto be employed in the production of pumpkin powder.The temperature of microwave-vacuum drying of thin layer pumpkin slice (2mm,4mmand 6mm)was studied by introducing a theoretical VMD mathematical model of carrot slice.The theoretical and experimental drying curves showed that the theoretical model was not inagreement with experimental data very well. The VMD model of pumpkin slice will beobserved in the further studies.
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