Effects Of Different Drying Methods On Raspberry Quality

Raspberry is loved by consumers because of its bright color,unique flavor and taste.At the same time because of its fruit is rich in amino acids,vitamins,anthocyanins,ellagic acid and other functional ingredients,has become a popular scientific research.However,the organization of raspberry is soft,fruit juice is rich in content,and the harvest season temperatures are high,it is difficult to store for a long time.This seriously reduces the quality of raspberry and the development of agricultural industrialization about raspberry has limited.Raspberry drying process can extend the raspberry shelf life,it is very important and practical significance for further development and utilization of raspberry.In order to improve raspberry drying efficiency,raise the quality of raspberry processed products and enrich product categories,raspberry as raw material in this paper,which collected from Shenyang Agricultural University raspberry test garden,the effects of five drying methods?natural drying,hot air drying,heat pump drying,explosion puffing drying and vacuum freeze drying?on physical properties,color,Vc content,anthocyanin content,total phenolic content,reducing sugar and total sugar content,SOD activity and antioxidant activity of raspberry dry products were studied.Based on the comparative analysis of these quality characteristics,we select the appropriate drying method that can preserve the nutritional value of raspberry.The response surface optimization of the processing parameters of this method was also carried out to determine the best raspberry drying technology and provide a theoretical basis for the raspberry drying processing.The first part mainly studied effects of five different drying methods on physical properties,color,nutrients and antioxidant activity of raspberry dried products.The experimental results showed that in terms of physical properties,the yield and texture characteristics of vacuum freeze-dried products are better than those of the other four drying methods.In terms of color,hot air drying,vacuum freeze drying and natural drying raspberry compared with fresh raspberry color value is smaller,better retention of color,and heat pump drying and explosion puffing drying raspberry color difference is larger.In terms of nutrients,vacuum freeze drying because of its lower drying temperature,shorter drying time and less contact with oxygen and other characteristics,the loss of nutrients was significantly less than the hot air drying and other four kinds of drying.Among them,Vc content was 74.06%of fresh raspberry;retention rate of anthocyanin was 54.24%;total phenolic content was 73.47%of fresh raspberry;retention rate of reducing sugar and total sugar was 79.80%and 99.45%;SOD activity is up to 863.9 U/g.In terms of antioxidant activity,vacuum freeze drying raspberry is better on DPPH free radicals,ABTS⁺radicals scavenging ability and Fe³⁺reduction ability.Based on the above evaluation,vacuum freeze drying efficiency is the highest.The quality of dried products,the nutrients of raspberry and antioxidant capacity is better,which is more suitable for drying.It can be applied to industrial production.The second part mainly based on the single-factor experiment,the Box-Behnken method experimental design method was used to establish the mathematical model of raspberry vacuum freeze-drying.The test of significance shows that the model can be used to reflect the actual problems.Through this quadratic regression model,the effects of drying time,heating plate temperature and drying chamber vacuum on the crispness,color difference and water content of raspberry dried products were analyzed.The study found that among the three factors,hot plate temperature was the most significant factor affecting the quality of vacuum freeze-dried raspberries.Through the comprehensive single factor experiment and response surface analysis,the best technology of raspberry vacuum freeze-drying was obtained.The results show:The optimum conditions of raspberry vacuum freeze-drying process were drying time 4.08 h,heating plate temperature 71.62?,drying chamber vacuum 62.76 Pa.With the actual production,verify the best process parameters.Set the process parameters:drying time 4 h,heating plate temperature 72?,drying chamber vacuum 63 Pa.The result is dry raspberry crispness1.765,color difference value 3.55,moisture content 3.31%.Response surface optimization effect is better,the measured value and the predicted value of a higher fit.It shows that the process parameters optimized by the response surface method have practical significance.