Analysis Of Polyphenols And Protein Composition Of Litchi Cloudy Juice Precipitation And Study On Its Stabilization Technology

Litchi cloudy juice tends to precipitate and brownish during storage.To study the material base of this phenomenon,,this paper analysed the factors of the instability of Lichee turbid juice and the possible material basis for the formation of the precipitate by tracking the changes of physical and chemical components in the storage process of litchi turbid juice.And the product of litchi turbid juice was developed by high pressure homogenization,adding stabilizer and antioxidant,which effectively improved the stability of Lichee turbid juice and inhibited the browning.The main results are as follows:1.Precipitation composition of lychee cloudy juice and physicochemical changes during storageLitchi turbid juice was stored at 4?and 25?for 10 weeks,and the physical and chemical changes are as follows:the longer the storage time and the higher the temperature,the more precipitation of cloudy litchi juice and the more serious browning.During the storage period,the total protein content of the cloudy juice decreased,while the contents of albumin,globulin,gliadin and glutenin in the precipitated protein increased.And the higher the temperature,the more obvious the change.The cloudy litchi juice after storage of the precipitate composition was analysed,the results showed that the total sugar,crude protein,total dietary fiber,ash content and total phenol content in the precipitate of litchi turbid juice accounted for 48.23?±0.88?%,27.47?±0.40?%,15.54?±0.51?%,2.43?±0.08?%,792.80?±2.93?mg/kg)of dry matter respectively.2.Structural identification of phenolic compounds and characteristics of crude protein componentsProanthocyanidins B₂ and quercetin-rutin-rhamnoglycoside of the litchi turbid juice supernatant decreased significantly,but the two phenolic compounds were not detected in the precipitation.In the process of storage,there was a new phenolic substance in the precipitation,which we are not determined,and may be a polymer formed after the oxidation of the original phenolic compounds.The subunit molecular weight of the supernatant protein and the globulin and gliadin in the cloudy juice of litchi mainly concentrated at 30-95 kD,which was much lower than that of glutenin??270 kD?.So glutenin with high molecular weight may directly deposite during storage.The denaturation temperature of the supernatant protein,glutenin and alcohol protein is lower than 95?.So in the process of fruit juice sterilization,some protein denaturation resulted in settlement.The free thiol content of supernatant protein,globulin and gliadin exceeded 50%of total sulfhydryl group,and the content of two sulfur bonds is low.It is easier to fold during storage,providing a basis for later exposure of protein active sites,as well as flocculation and sedimentation.3.Study on the control technology of the stability of litchi turbid juiceThrough single factor and correlation experiment analysis,the best homogenization condition is obtained as follows:the pressure is 20 MPa and the average number of times is three.The optimum stabilizer ratio of pectin,CMC and xanthan gum was 1.39,3.50 and 0.50 g/L respectively.The best antioxidants of ascorbic acid,L-cysteine and sodium sulfite were 6.00,1.14 and 0.07 g/L respectively.