Effects of Chemical Osmotic Pretreatment on Drying Characteristics and Quality of Blueberry under Hot Air Drying

In order to study the effects of chemical osmotic pretreatment on the characteristics and quality of blueberry under hot air drying,fresh blueberries were pretreated with 2.5 g/100 mL K2CO3+0.6 g/100 mL olive oil,and 5.0 g/100 mL K2CO3+0.6 g/100 mL olive oil at(45±0.5)℃,respectively.The changes of water content,rehydration,hardness,microstructure,color difference,active ingredient anthocyanin,total phenol and DPPH radical scavenging capacity of dried blueberries in different treatment groups under hot air drying were compared and analyzed.The results showed that the dehydration rates of blueberries vary greatly according to the type of pretreatments when the samples were dried to the same water content with hot air.Specifically,the dehydration rate of dried blueberries pretreated by 5.0%K2CO3 solution was the highest,followed by 2.5%K2CO3 osmotic pretreatment and lastly the control group;the corresponding dehydration time was 10,14 and 20h,respectively.The physical qualities of dried blueberries,involving the browning degree,color difference,rehydration and microstructure,were significantly different between the chemical osmotic pretreatment group and the control group(P<0.05).The chemical osmotic pretreatment of K2CO3 solution increased the dehydration rate of the samples,shortened the drying time and maintained the quality of blueberries dried with hot air.There was no significant difference between the physical quality of dried blueberries pretreated by 2.5%and 5.0%K2CO3 solution(P>0.05),whereas there was significant difference in drying time and nutrient quality which is characterized by total phenols,anthocyanins,DPPH radical scavenging rate,soluble total sugar(P<0.05).Conclusion:5.0%K2CO3 osmotic pretreatment combining with hot air drying can improve the dehydration rate,shorten the drying time and maintain the physical and nutritional quality.