Study On The Combined Drying Process And Quality Of Strawberry

With the development of science and technology and the improvement of people's living standard,the demand for diversified and high-quality dehydrated fruit and vegetable products is increasing.Combined drying as the preparation of high-quality fruit and vegetable crisp is gradually favored by researchers.Due to the technical characteristics such as the high-pressure difference and the low-temperature,carbon dioxide differential puffing(CDP)can not only control the texture of fruit and vegetable materials,but also better retain the heat sensitive nutrition.Therefore,the purpose of this study is to enhance the quality of strawberry slices by exploring an appropriate combined drying method in CDP combined with hot air drying(HAD),vacuum drying(VD),and vacuum freeze-drying(FD).Scanning electron microscope(SEM)and the mercury injection technology were used to analyzed the quality changes between the different combined drying methods.The principal component analysis was used to selected the combined drying method with higher comprehensive quality.The response surface optimization(RSM)was used to optimize the parameters of the combined drying process of strawberry slices.The main conclusions of this study were as follows:1.Study on the characteristics of HAD,VD and FD of strawberry.Under different single drying methods,the total drying time of strawberry slice products was FD,VD and HAD from high to low.The Wang and singh model,Logarithmic model,and Two-term exponential model were the optimal models of HAD,VD,and FD of strawberry respectively.2.Effects of different combined drying methods on the quality of strawberry slices.The effects of nine combined drying modes(CDP coupled with FD,HAD and VD)on the sensory evaluation,color,shrinkage,hardness,brittleness,microstructure,pore structure,nutrition and total energy consumption of strawberry slices were studied.Comprehensive analysis shows that the overall sensory score of FD+CDP+FD strawberry slices was the highest.The ?a value of HAD+CDP+HAD strawberry slices was the lowest,and the ?a value of VD+CDP+FD strawberry slices was the highest.There was no significant difference in the ?E value of strawberry slices gained by different combined drying methods.The shrinkage,crispness and hardness of FD+CDP+FD strawberry slices were the lowest,followed by those of VD+CDP+FD,FD+CDP+VD and VD+CDP+VD strawberry slices.The best porosity and nutrient index could be obtained by FD+CDP+FD strawberry slices.The porosity,average pore size,total pore volume,vitamin C,total anthocyanins and flavonoids contents of FD+CDP+FD strawberry slices were the highest,followed by FD+CDP+VD,VD+CDP+FD and VD+CDP+VD,which were all higher than those of HAD strawberry slices.The total energy consumption of HAD+CDP+HAD(10.09�0.23 KWH/kg)was the lowest,but that of FD+CDP+FD(19.04�0.19 KWH/kg)was the highest.The scanning electron microscopy(SEM)showed that the tissues of VD+CDP+VD,VD+CDP+FD,FD+CDP+VD and FD+CDP+FD strawberry slices were loose and the holes were clear.The results of principal component analysis and correlation analysis of 18 evaluation indexes showed that the sensory evaluation,shrinkage rate and crispness were the core quality indexes,and the comprehensive scores of FD+CDP+VD and VD+CDP+VD were 0.6297 and 0.6313,respectively.3.Optimization of VD+CDP+VD strawberry slice.Response surface methodology(RSM)was used to optimize the combined drying process of VD+CDP+VD strawberry slices.The optimized parameters of VD+CDP+VD strawberry slices were as follows: the moisture content of pre-drying was 38.26%,the pressure difference of CDP was 2.77 MPa,the residence time of CDP was 50 min.The moisture content had the greatest effect on the quality of strawberry slices,followed by the pressure difference of CDP and the residence time of CDP.4.Optimization of FD+CDP+VD Strawberry slices.Response surface methodology(RSM)was used to optimize the combined drying process of FD+CDP+VD strawberry slices.The optimized parameters of FD+CDP+VD strawberry slices were as follows: the moisture content of pre-drying was 35.64%,the pressure difference of CDP was 2.83 MPa and the residence time of CDP was 47.13 min.The effect of the pressure of CDP on the quality of strawberry slices was the greatest,followed by the residence time of CDP and the moisture content.5.Comparison in quality of strawberry slices gained by combined drying method and single drying method.The scores of overall sensory evaluations of VD+CDP+VD and FD+CDP+VD strawberry slices were 95.30�0.23 and 96.18�0.18,respectively,higher than those of FD and shrunken FD strawberry slices.The shrinkage rate of VD+CDP+VD and FD+CDP+VD strawberry slices was 18.13�0.09% and 12.82�0.10%,respectively.The crispness of VD+CDP+VD and FD+CDP+VD strawberry slices was 6.78�0.10 mm and5.72�1.06 mm,respectively,higher than those of FD and shrunken FD strawberry slices.Factor analysis was used to analyze the quality indexes of four strawberry slices.The results showed that the comprehensive score ranked form high to low as FD+CDP+VD,VD+CDP+VD,FD strawberry slice,and shrunken FD strawberry slices.In conclusion,quality and crispy strawberry slices could be obtained by FD+CDP+VD and VD+CDP+VD.