关键词: 苹果片, 气体射流冲击干燥, 品质评价, 响应面, 综合优化

Abstract:

【Objective】 In order to obtain the drying process parameters of apple slices with high quality and low energy consumption, the effects of air temperature, slice thickness, air velocity and their interaction on the vitamin C (V_C) content, rehydration ratio and energy consumption were investigated during the air-impingement drying of apple slices. 【Method】 With the air temperature, slice thickness and air velocity as the factors, and the three-factor response surface Box-Behnken response surface design was carried out with the V_C content, rehydration ratio and unit energy consumption of apple slices as the response. The factors and their interactions between the various factors were analyzed, and a quadratic regression model of V_C content, rehydration ratio and unit energy consumption was established and verified by applying three optimization methods, including genetic algorithm, fgoalattain function method and membership degree comprehensive evaluation method, were applied respectively. 【Result】 The factors’ order of influencing on the Vc content was as the follows: Air temperature, slice thickness and air velocity. Regarding the air temperature, both the interactions between the slice thickness and the air velocity were extremely significant, respectively. The factors’ influencing rehydration ratio ordered as the air temperature, air velocity and slice thickness, and all these factors had an extremely significant effect; the interactions between slice thickness and air velocity were significant. The orders influencing on the energy consumption were the slice thickness, air temperature and air velocity. And the air temperature, slice thickness and the interactions between air temperature and air velocity were extremely significant, air velocities and the interactions between air temperature and slice thickness were significant. The established regression model of V_C content, rehydration ratio and energy consumption was statistically significant (P<0.05), suggesting that the model could be used to analyze and predict air-impingement drying parameters. The optimal drying parameters analyzed by genetic algorithm were of 63.24℃ air temperature, 2.00 mm slice thickness and 12.00 m·s ^-1air velocity, respectively. Under these conditions, the V_C content, rehydration ratio and energy consumption of apple slices were 66.96 μg/100 g, 3.83 and 26.49 kJ·g ^-1, respectively; the optimal process parameters obtained by fgoalattain function were as: air temperature 71.62℃, slice thickness 2.37 mm, air velocity 11.18 m·s ^-1, and V_C content was 64.90 μg/100 g, rehydration ratio was 3.41, and unit energy consumption was 25.85 kJ·g ^-1; the optimal process parameters obtained by the comprehensive evaluation method of membership degree were as: air temperature 63.57℃, slice thickness 2.00 mm, air velocity 12.00 m·s ^-1, and V_C content was 66.94 μg/100 g, rehydration ratio was 3.79, unit energy consumption was 26.53 kJ·g ^-1. With the fitness value as the index, it could be concluded that the genetic algorithm optimized results were the best. 【Conclusion】The genetic algorithm could be used for the multi-objective optimization in air-impingement drying apple slices. The optimum parameters were of 63℃ air temperature, 2 mm slice thickness, and 12 m·s ^-1air velocity. With these parameters, the V_C content, rehydration ratio and unit energy consumption under this parameter were 66.85 μg/100 g, 3.78, and 26.59 kJ·g ^-1, respectively. In conclusion, the air-impingement technique could be applied in the drying of apple slices with high V_C content, high rehydration ratio and low energy consumption.

Key words: apple slice, air-impingement drying, quality evaluation, response surface, comprehensive optimization