Characterization Of Osmotic Dehydration Based Combination Drying Of Chili Pepper

At present,with the constant improvement of food quality including taste,color and quality,dehydrated vegetable becomes one of the most important export products in China.Dehydrated vegetable is not only easy to store but also to transport.But in the process of dehydration,it needs to improve the drying rate and make sure that the quality of dehydrated vegetable is not affected or just affected slightly.Scientific drying method for vegetables is required in the drying process.Combined drying technology develops rapidly because of advantages of low cost,high efficiency and good quality.In this study,the characteristics of osmotic dehydration of chili pepper were investigated by experiments of osmotic dehydration,using temperature,osmotic time,different osmotic solutions as factors,and the handling process of osmotic dehydration of the chili pepper was optimized.After osmotic dehydration,the chili pepper was selected for hot-air drying and infrared drying test,and the characteristics of osmotic dehydration,osmosed hot-air drying,osmosed infrared drying,rehydration,and quality of chili pepper were investigated by experiments of osmotic dehydration,osmosed hot-air drying,osmosed infrared drying and rehydration,using water loss,solids gain,water loss and solids gain ratio,effective moisture diffusion coefficient,activation energy,VC retention rate,pungency degree,rehydration rate,recovery rate,and sensory evaluation as indices.As a result,good reference can be given for the process and storage of chili pepper with high quality and low cost to improve the drying technology and industrialization of the chili pepper products.At the same time,the basic drying theory of chili pepper was studied and drying mathematical model was established,and the accurate simulation of the drying characteristics was expressed.It has certain academic significance and value of design and development for high performance drying equipment.The study can provide data support which depends on analysis of the influence of different factors,optimization of drying process parameters and improvement of drying efficiency.The main conclusions of this study are as follows:Firstly,with increase of temperature or salt content of the osmotic solution,water loss and solids gain of chili pepper increase.After osmotic dehydration of 2 h,4 h and 6 h in osmotic solution of 45% sugar plus 10% salt with solution temperature 45oC,the values of water loss and solids gain ratio of the chili pepper are 4.31±0.12,5.21±0.10 and 5.74±0.13,respectively.Air temperature is the main factor that affects the infrared drying,followed by air speed.The optimal air temperature range for chili pepper drying is 45~50oC,and under the same drying condition,moisture content of osmosed hot-air drying sample can meet storage moisture requirement earlier than that of direct osmosed infrared drying sample.The moisture content of chili pepper sample decreases from 82.4% to 72.3% after osmotic dehydration of 1h in osmotic solution of 45% sugar plus 10% salt with solution temperature 45oC,and the drying time of chili pepper after osmotic dehydration shortens 1-2 hours,resulting in decreases of energy consumption and cost during drying process.Effective moisture diffusion coefficient of chili pepper almost linearly increases with increase of air temperature during hot-air drying.For air speed of 1.8m/s,activation energy of direct hot-air drying and osmosed hot-air drying are 53.25±1.08 kJ/mol and 44.42±0.88 kJ/mol,respectively.Secondly,range analysis and variance analysis results show that the optimal infrared drying process for chili pepper is: drying temperature 55oC,radioactivity distance 50 mm and laying thickness 6mm.Drying temperature is the main factor that affects the infrared drying,and it is followed by laying thickness.Vc retention rate,pungency degree,rehydration rate and recovery rate of chili pepper sample processed by osmosed infrared drying are higher than those processed by direct infrared drying,and the characteristics of rehydration and quality of the former sample are better than the latter one.Thirdly,drying curves obtained were processed to find the most convenient model among 10 different models defining drying rates given by several authors.The results showed that Page Model is the best kinetics model for describing the drying characteristics of chili pepper under conditions studied,and it has the highest values of coefficient of correlation and the lowest values of chi-square and root mean square error,which can well describe the drying characteristics of chili pepper.The Page Models for describing the infrared drying and hot-air drying characteristics of chili pepper were built and validated as well,and the results showed that the Page Model is the best mathematical model for these drying processes.