A three‐stage microwave‐vacuum, pulsed‐vacuum, and vacuum drying method for lotus seeds

Abstract

In this study, a three-stage microwave-vacuum, pulsed-vacuum, and vacuum drying method (MVD-PVD-VD) was proposed to reduce the quality loss of dried lotus seeds. The effects of MVD-PVD-VD, double combination of microwave vacuum drying, and pulsed vacuum drying (MVD-PVD), PVD, MVD, VD, and hot air drying (HAD) on the quality of lotus seeds were comparatively investigated. Results showed that MVD-PVD-VD took some advantages over the other four drying methods as it allowed the lowest shrinkage, and the highest porosity, rehydration capacity, total phenolic content, and nine phenolics contents. It was shown that with the decreasing moisture content of conversion point for the changing of MVD into PVD and PVD into VD during MVD-PVD-VD, the required drying time and shrinkage ratio decreased, and porosity and rehydration capacity increased. This study demonstrated that MVD-PVD-VD is an effective alternative method for the drying of lotus seeds. Practical applications Lotus seeds, the mature fruit from the Nelumbo nucifer, are important commercial crops and widely consumed as dietary staple or dietary supplement in many countries. Because of its perishable characteristic, fresh lotus seeds must be dehydrated to extend its shelf-life for off-season use. Drying is one of the most important and worldwide spread methods for food preservation. However, conventional drying methods are time-consuming and may cause significant loss in the quality of the product. To this end, a three-stage microwave-vacuum, pulsed-vacuum, and vacuum drying method are proposed in this paper to dehydrate lotus seeds. Results showed that this method is an effective alternative method for the drying of lotus seeds.