Development of dehydration process for heat sensitive biological and agricultural products using microwave vacuum technology

Abstract

The objectives of this research were; 1) to design and develop a microwave vacuum dehydration system; 2) to commission and test the microwave vacuum dehydration system and 3) to compare the effectiveness with conventional dehydration methods. A microwave vacuum dehydration system was successfully developed for dehydration of heat sensitive materials such as biological and agricultural products. Microwave is recognized as a fast heating process characterised by volumetric heating. Contrary to conventional dehydration method which heats from the surface of material, microwave heats material from inside out. Incorporation of vacuum enhances the microwave dehydration process by allowing water to vaporize at lower temperature. Thus, dehydration of heat sensitive materials can be achieved at low temperature and shorter time thereby preventing degradation of nutritional values and texture. Commissioning and testing of the developed microwave vacuum dehydration system showed that the system is capable to produce good quality of dehydrated products. This can be achieved by adjusting microwave power and vacuum pressure. In comparison of different dehydration methods for jackfruit, it was found that vacuum microwave dried sample had higher rehydration potential, better in colour, aroma and structure, lower density and softer texture than hot air dried products. The hot air dried products were darker in colour, hardness and shrunken. Less discolouration and structural changes occurred in vacuum microwave drying. Although freeze dried product was the highest in rehydration potential and structural retention, the vacuum microwave dried product however was rated as equal to or better than freeze dried products in terms of colour, aroma and overall preference in both the dehydrated and rehydrated state.