Effect of Microwave-Vacuum Drying on Drying Characteristics and Quality of Mulberry

บทคัดย่อ

Mulberries (Morus nigra) are rich in antioxidants and essential bioactive substances that human body is not able to produce them. Mulberries are used effectively in folk medicines, e.g., treat fever, protect liver and kidney from damage, and lower blood pressure. However, mulberries are high moisture content fruits and extremely sensitive to storage. In addition, their harvesting seasons are very short. Drying to lower moisture content for prolonging shelf life and for further usage in other food applications is needed. The application of microwave-vacuum drying (MVD) is promising since MVD leads to higher drying rate and yields the dried product of better quality. In this study, microwave-vacuum drying of mulberries was investigated. Fresh mulberries with initial moisture content of 810 % (db), water activity of 0.98, were dried at various microwave powers (65, 120 and 170 W) and absolute pressures (41.33, 31.33 and 21.33 kPa) until the final moisture content of 12 % (db), water activity of 0.55, were reached. The results revealed that the microwave power and absolute pressure levels significantly influence on drying characteristics and qualities of the MVD mulberries, viz., color and hardness. Thus, the optimum condition for microwave-vacuum drying is at microwave power of 120 W and absolute pressure of 21.33 kPa.