Technologic parameter optimization in pilot-scale process of heat pump drying of Areca catechu L.

Abstract: Areca catechu L. belongs to perennial aiphyllium of palmae. It has very high medicinal value and is regarded as the first one of 4 kinds of the south medicines in China. Areca catechu L. abounds in Hainan, 10% for fresh food, more than 90% dried for further processing, Areca catechu L. drying has become the important processing industry in Hainan, the annual output of dried betel nut is about 200 000 t, and the annual output value is more than 10 billion yuan. For the Areca catechu L. drying, there are hot air drying and vacuum freeze drying, which have not been applied in production because of the limitation of experimental conditions and equipments, and the traditional furnace drying, steam drying and heat pump drying are used in production. The traditional furnace drying is a kind of small workshop processing, and its characteristics of small scale, large labor intensity and serious pollution are difficult to adapt to the modern agriculture development, so it has been gradually eliminated. For the steam drying whose heat source is from the burning coal, the characteristic of large scale and high mechanical strength adapts to the intensive agricultural product processing development, however it is limited because of a lot of greenhouse gases emitted from burning coal. Only the energy-conservation and environment-protection drying method is suitable for the Areca catechu L. drying industry's sustainable and healthy development. The betel nut drying was studied using the heat pump drying equipment in this paper. The influences of boiling time on betel nut hardness, and drying temperature and loading capacity on moisture content of dried fruit were analyzed via the single factor experiment. The technology parameters of heat pump drying were optimized by the orthogonal experiment, and the quality of the dried betel nut was evaluated using the weighted score method. After 30-day storage, the physical, chemical and microbiological indicators of the dried fruits were detected, and moreover, the advantages and benefits were analyzed based on the comparison between the heat pump drying method and the steam drying and traditional drying methods. The optimum drying parameters were: boiling time of 15 min, initial drying time of 12 h at 50 ℃, following drying time of 84 h at 65 ℃, loading capacity of 3.5 t, 25% air relative humidity of dried room, and 16.8% water content of betel nut. The results showed as follows: the ratio of good dried fruit was 96%, the uniformity of dried fruit was 91%, the power consumption of dried fruit was 0.92 (kW·h)/kg, the comprehensive score of dried betel nut quality was 90.1, and the color of dried fruit was either olive yellow or brown. After 30-day storage at 25℃, the dried fruit did not mildew, and the physical and chemical indicators were in the controllable range. The cost of drying betel nut by heat pump was more economical, 11% lower than that of the steam drying and 50% lower than that of the traditional drying. The heat pump drying had the advantages of energy saving, low emissions, intelligent operation, low drying cost and good economic benefit. The research results provide the technical reference for the standardized processing of the betel fruit with the heat pump drying method.