Microwave Combined With Thermosonication For Browning Inhibition In Apple Whole Fruit Juice

Apple juice produced by whole apples(WAJ)contains abundant nutrients.The enzymatic browning and sedimentation of apple juice during manufacturing and storage significantly impede its industrialization.In this study,microwave,ultrasound and heat treatment technologies were applied to solve those problems during the WAJ juice production.The changes in color and quality of the WAJ juice during the processing and storage were studied.On the basis of the application of these combined technologies,the browning of WAJ juice was inhibited.This provides a technical basis for industrialized production of WAJ juice.The main results and conclusions are as follows:(1)The whole apple was pretreated by microwave under different conditions.The browning index,total phenols,polyphenol oxidase activity,soluble quinone and antioxidant activity of the apple juice were investigated.Principal components analysis(PCA)was used to analyze various indicators for optimization of the microwave pretreatment condition.The results showed that microwave pretreatment significantly inhibited the browning of apple juice,decreasing the activity of polyphenol oxidase and increasing the total phenol content and antioxidant capacity of apple juice(p<0.05).The PCA showed that the optimum microwave treatment conditions were 800 W and 140 s.The browning index,polyphenol oxidase activity and soluble quinone content of apple juice were 30.1%,32.5%and 17.3%less than these obtained from the blank group,respectively.The total phenol content was 2.2 times higher than that in the blank group.These results indicated microwave pretreatment can be used to inhibit the enzymatic browning of WAJ juice.(2)By comparing browning index,polyphenol oxidase activity and total phenol content of WAJ juice prepared by microwave pretreatment under 800 W,140 s and traditional thermal inactivation(85?,15 min),the microwave pretreatment significantly improved the color of apple juice(p<0.05)and the mechanism of the microwave pretreatment on WAJ juice color improvement was also investigated.The results showed that the significant inhibition of browning of WAJ juice prepared by microwave pretreatment under 800 W and 140 s were mainly due to the reduction of the activity of polyphenol oxidase in a short time without oxygen,destroy the structure of apple cell structure and increase the total phenol content of apple juice.It could be a potential approach to manufacture WAJ juice without browning(3)The thermosonication sterilization was applied in the WAJ juice.By comparing to traditional thermal sterilization(100?,10 min),and pasteurization(65?,30 min)treatment,optimum thennosonication sterilization condition was 50?,8 min.6 W/L,which was selected by single factor and orthogonal test.In addition,the degree of inhibition non-enzymatic browning was determined by the color,total phenol,reducing sugar,amino acid and other indicators.The results showed that the thermosonication sterilization effectively delayed Maillard reaction during sterilization(p<0.05)and inhibited phenolic oxidative polymerization during storage.Thermosonication sterilization is a promising approach to inhibit non-enzymatic browning of WAJ juice.