Research On Microwave-vacuum Freeze-drying Technology Of Oyster Mushroom And Development Of Its Crispy Skin

Pleurotus ostreatus is one of the main fungi cultivated in China.It is rich in protein,vitamins,and minerals.It is not only delicious,but also has many physiological functions such as anti-tumor,anti-oxidation,reducing blood lipid,and immune-enhancing activity.At present,the contrast of drying method and microwave-vacuum freezing combined drying technology of Pleurotus ostreatus have not been reported yet.In this paper,microwave drying,vacuum freeze drying and microwave-vacuum freezing combined drying of Pleurotus ostreatus were processed to optimize the best drying method.By the optimized method,platy mushroom crisp snacks were manufactured.The main research contents and results are as follows:(1)Using fresh Pleurotus ostreatus as raw material,the dry moisture content,drying rate,rehydration ratio,sensory score,color difference,texture,microstructure and unit energy consumption of Pleurotus ostreatus were used as indicators to compare the effects of microwave drying and vacuum freeze drying on dried Pleurotus ostreatus products.The results show that all aspects of microwave-vacuum freezing combined drying are in moderate conditions.Therefore,this experiment will use microwave-vacuum freezing combined drying technology optimize the drying process of Pleurotus ostreatus.(2)In order to obtain the optimal drying process of Pleurotus ostreatus and improve the quality of its dried products,this experiment adopts the microwave-vacuum freezing combined drying process.Use the Box-Benhnken design(BBD)method of Design-expert software to designed experiment.The single factor and response surface test methods were used to analyze the effects of microwave power,conversion point moisture content and vacuum freeze drying time on the dry basis moisture content,drying rate,rehydration ratio and sensory score of dried Pleurotus ostreatus.According to the experimental data,the quadratic regression model of four indicators was obtained,and the response surface analysis was carried out.The optimized drying process of Pleurotus ostreatus was as follows:microwave power 300W,conversion point moisture content 37%,vacuum freeze drying time 11h.Finally,the nutrient content of the dried Pleurotus ostreatus product(in dry basis)under the optimal process conditions was determined,and the protein content in the dried product was 26.5%,the crude fat content was 2.20%,and the total sugar content was 49.8%.Under this condition,the product index regression model was established,and the two-stage moisture prediction equation was obtained:MR=exp(-0.09883t-0.19858t1/2)and MR=0.47945exp(-4.33333t).The regression model has a high coefficient of determination and a good fitting degree.The theoretical value of the statistical model established by the regression analysis method is highly consistent with the experimental value and can be used for predicting the results in the drying process of Pleurotus ostreatus.(3)Fresh Pleurotus ostreatus as raw material,based on the microwave-vacuum freeze-drying optimal process,using four kinds of different pretreatments:blanching ultrasonic impregnation,blanching seasoning boiled,fumigation ultrasonic impregnation and cellulase treatment to dispose Pleurotus ostreatus.Then prepare Pleurotus ostreatus crisp snack foods.After comparative analysis of its moisture content,color,hardness,brittleness and sensory evaluation,the Pleurotus ostreatus prepared by the cellulase treatment method has excellent quality such as gray color,no curl at the edges,rich flavor of the Pleurotus ostreatus and moderate crispness.