Comparative study of three drying methods: freeze, hot air- assisted freeze and infrared-assisted freeze modes
Comparative study of three drying methods: freeze, hot air- assisted freeze and infrared-assisted freeze modes
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作者：
T. Antal
在三种干燥方法下进行脱水试验，以评估干燥曲线和能量吸收。苹果（Malus arteritica L.）在不同的加工条件下干燥立方体，应用冷冻干燥（FD）、热空气辅助的冷冻干燥和红外辐射辅助的冷冻干燥。使用常规冷冻干燥而不进行预干燥来制备对照样品。研究了在60 ° C和80°C空气温度下的热空气与冷冻干燥（HAD-FD）的组合。红外冷冻干燥（IR-FD）是一种较新的加工方法。采用5 kWm-2的红外功率强度对苹果块进行干燥。结果表明，红外辐射功率和热风温度对冷冻干燥的干燥速率和干燥时间有影响。在预脱水过程中，红外辐射加热的干燥速率高于热风加热.测定了成品的水分活度、色泽、硬度和复水率。与HAD-FD干燥相比，IR-FD干燥的物料色泽好，复水率高，硬度低。单级FD样品的质量接近IR-FD材料。据观察，与FD和HAD-FD干燥处理相比，IR-FD方法显著降低了能量消耗。食品物料的干燥动力学一般采用Henderson-Pabis模型和三次多项式模型。结果表明，这些数学模型能够较好地预测含水率的变化。
The dehydration tests were conducted at three drying methods to evaluate the drying curves and the energy uptake. Apple ( Malus domestica L.) cubes were dried under different processing conditions applying freeze drying (FD), freeze drying assisted by hot air and freeze drying assisted by infrared radiation. Control samples were produced using regular freeze drying without the pre-drying. Hot air combined with freeze drying (HAD-FD) at 60 and 80°C air temperatures was investigated. The infrared-freeze drying (IR-FD) is a relatively new processing method. The Idared apple cubes were dried with 5 kW m -2 IR power intensity. It was observed that the infrared power level and hot air temperature affected the drying rate and time of freeze drying. The infrared radiation heating had a higher drying rate than hot air during the pre- dehydration. The water activity, colour, firmness and rehydration ratio (RR) of finished products were measured. The dried material produced with IR-FD had desirable colour, higher rehydration rate and lower firmness than dried by HAD-FD ones. The quality of single-stage FD samples was close to IR-FD materials. It was observed that the IR-FD method drastically decreased the energy consumption, compared to FD and HAD-FD drying treatments. The mathematical models such as Henderson-Pabis and third-degree polynomial are used to describe the drying kinetics of food material. It was found that those mathematical models performed adequately in predicting the changes of moisture ratio.