A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development

Thesis (M. Sc.) - Asian Institute of Technology, 2018

Purple sweet potato is one of the superfood with good nutraceutical properties. A large amount of purple sweet potato was decayed during storage due to its high moisture content. Dehydration process can prevent such loss. Microwave vacuum drying is alternative drying method that can dry food materi als faster than conventional methods and preserve its quality. Fabricating an affordable microwave vacuum drying is proved to be successful by modifying the commercial microwave oven. Drying kinetic s and mathematical modeling is studied to explain the beha vior of purple sweet potato dehydration process under microwave vacuum dryi ng. P retreatment effect also included in this study. The time required to dry 53.5 g of purple sweet potato slice by microwave vacuum drying is ranging from 6.5 - 14 minutes depend on the power level of the microwave as well as the pretreatment that was conducted to the samples. The constant drying rate of the pretreated samples is higher compare d to the untreated sample, although it takes longer time to dry, for example i n 600 W power level, the drying of was 8 minutes and 10 minutes for untreated and pretreated samples respectively. Effective moisture diffusivity of the purple sweet potato in microwave vacuum drying is in the range of 10 - 7 g/(g min). The best mathematical model to be used in this experiment is logarithmic model with R 2 value was more than 0.99. Physical properties of the dried product from microwave vacuum drying was harder in texture and more purple in term of color. WAI, WSI, and SC of both powder was observed with almost no significant different . Microwave vacuum drying was proven to be better drying method than hot air drying in preserving the anthocyanin and phenolic compounds of purple sweet potato. The powder from mic rowave vacuum drying also has higher antioxidant activity. Blanching can be used as pretreatment which lead to better physical properties than untreated samples.