双孢菇微波冷冻干燥特性及干燥品质

为获得干燥时间短、产品质量高的蘑菇制品,采用微波冷冻干燥技术对双孢菇进行干燥处理,研究其在不同微波比功率(0.25,0.5,0.75 W/g)和系统压强(50,100,150 Pa)下的干燥曲线、有效水分扩散系数、复水比、收缩率、白度、维生素C保存率、能耗及基于模糊数学推理法下感官评定的变化规律;通过非线性拟合建立了适用于双孢菇微波冷冻干燥的数学模型;基于干燥能耗、干燥时间及部分品质指标对不同条件下双孢菇微波冷冻干燥过程进行加权综合评价。结果表明:微波比功率对干燥速率及干制品物理品质指标影响比对其他指标的影响更显著(P0.05);系统压强对干制品营养含量指标、干燥能耗以及感官评定的影响比对干燥特性的影响显著(P0.05);采用Henderson and Pabis模型能够准确(R20.9)描述干燥过程中水分变化规律;双孢菇有效水分扩散系数在10-10 m2/s数量级且受微波比功率影响更明显(P0.05);微波比功率和系统压强过高会造成双孢菇干制产品不被消费者接受;当微波比功率和系统压强分别为0.25 W/g和100 Pa时双孢菇微波冷冻干燥的综合评分值最高为0.67847,该条件较适合应用于双孢菇微波冷冻干燥中。研究探索了不同微波冷冻干燥条件下双孢菇干燥及品质特性的变化规律,为双孢菇微波冷冻干燥较优工艺参数组合的选择提供了理论依据。

Drying characteristics and quality of button mushrooms during microwave freeze drying

Abstract: Button mushroom is the most widely cultivated and consumed mushroom throughout the world and it contributes about 40% of the total world production of mushroom. Button mushrooms are extremely perishable and their shelf life is only about 24 h in ambient conditions. Various physiological and morphological changes occur after harvest, which make these mushrooms unacceptable for consumption. Hence, they should be consumed or processed promptly after harvest and for this reason the mushrooms are traded mostly in dried form in the world market. The convective drying method is the most commonly used to dry mushrooms. Nevertheless, due to long drying time and high drying temperature at industrial scale, the problems of darkening in color, shrinkage, loss in flavor and decrease in rehydration ability easily occur. In recent years, microwave freeze drying (MFD) has been investigated as a potential method for obtaining high quality dried food products with low energy consumption. Thus, to achieve faster drying rate with high product quality, MFD was applied to dry button mushrooms. The drying curves, effective moisture diffusivity, rehydration ratio, shrinkage ratio, vitamin C retention ratio, energy consumption and the sensory evaluation based on the fuzzy reasoning were investigated, which were considered to reflect the drying and quality characteristics of button mushrooms under different microwave loading levels (0.25, 1.0 and 0.75 W/g) and system pressure (50, 100 and 150 Pa). The drying models were obtained by the nonlinear fitting of drying curves. The weighted comprehensive evaluation of button mushroom MFD processes were also carried out based on energy consumption, drying time, rehydration ratio, whiteness index and vitamin C retention ratio. Results showed that, when changing the microwave loading level, the reduction ratio of the minimum value to the maximum value of drying time, effective moisture diffusion coefficient, whiteness index, rehydration ratio and shrinkage ratio were higher than those obtained by changing the system pressure. It meant the microwave loading level had a more significant influence on drying rate and physical quality index than the system pressure. However, the system pressure had more obvious influence on nutritional content index, energy consumption and sensory evaluation compared to the microwave loading level. Through the nonlinear fitting function of Origin pro 8.5, we found the R-square of Henderson and Pabis model fitting curve was the highest, which implies the Henderson and Pabis model could well describe the moisture variation in drying process; the effective moisture diffusion coefficient of button mushrooms during the MFD was in the range of 3.423×10-10-5.654×10-10 m2/s, and it was on the 10-10 m2/s order of magnitude and more influenced by microwave loading level. In addition, the products obtained under high microwave loading level and system pressure would be not accepted by consumers. Taking energy consumption, drying time, rehydration ratio, whiteness index and vitamin C retention ratio into account, 0.25 W/g microwave loading level with 100 Pa system pressure was proposed as the favorable condition for button mushroom MFD. The results provide a theoretical basis for the selection of the suitable processing technology for the MFD of button mushroom.