关键词: 云南小粒速溶咖啡, 真空冷冻干燥, 初始孔隙, 参数优化

Abstract: In order to explore the optimal technological parameters of vacuum freeze‑drying of unsaturated Yunnan small grain instant coffee, by using Yunnan small instant coffee concentrate as the main raw material, the unsaturated material was prepared by “liquid nitrogen ice cream process” for vacuum freeze drying. On the basis of single factor experiment, Box-Behnken design in response surface method was used to investigate the effects of drying temperature, drying pressure, specific surface area and their interaction on sensory evaluation, unit energy consumption and drying time. The regression equation was established to obtain the optimal process parameters. The results show that the vacuum freeze‑drying process is always in the stage of slowing down. The higher the drying temperature is, the greater the drying rate is and the faster the moisture content decreases. The larger the specific surface area of the sample is, the higher the drying rate is and the faster the moisture content drops. The specific surface area of the sample has significant effects on sensory scores (P<0.01), and the drying temperature, drying pressure and specific surface area of the sample has significant effects on unit energy consumption (P<0.01). Drying temperature and specific surface area of samples has significant effects on drying time (P<0.01). The optimized drying parameters are as follows: drying temperature 58 ℃, drying pressure 50 Pa, sample specific surface area 4.13 cm2/g. Under these conditions, the sensory score of unsaturated Yunnan small instant coffee is 7.62, unit energy consumption is 2.81 kJ/g, and drying time is 275 min.

Key words: Yunnan small grain instant coffee, vacuum freeze?drying, initial pore, parameter optimization