Abstract:To improve the quality and efficiency of single-batch mass drying of wolfberry, a room-temperature vacuum drying system was designed and manufactured to have a capacity to dry 1 125 kg of fresh wolfberry fruits per batch. On the basis of no-load test results, the drying efficiency of the system for wolfberry was studied by side pumping, end pumping, and combined pumping. The vacuum capacity and heating capacity of the system were experimentally proved to meet the design requirements. During vacuum drying at room temperature, the water loss rate of wolfberry peaked at 4 kg/h and then gradually decreased to 1.5 kg/h with drying time. Compared with end pumping and combined pumping, side pumping resulted in a shorter drying time (7.00% and 3.13% less, respectively) and a higher dehumidification efficiency (29.27% and 19.23% higher, respectively). As the drying temperature decreased (from 60 to 53 ℃), the proportion of high-quality dried wolfberry fruits gradually increased (from 54% to 79%), and the proportion of air-filled wolfberry fruits gradually decreased. Local temperature and humidity uniformity in the drying oven is an important factor affecting these proportions in the final dried wolfberry products. The research results lay a foundation for the development of a room-temperature vacuum-drying system with a capacity to dry 4 tons of fresh wolfberry fruits per batch, while providing a reference for the development of these systems for fruits, vegetables, and Chinese herbs as well as for optimizing the final vacuum-dried products of wolfberry.
