The Research On The Processing Technology Of Concentrated Litchi Juice

The effects of reduced pressure concentration on the quality of litchi juice were researched with litchi juice. The results indicated that the total soluble solids in litchi juice were increasing with concentrated times increase, but the titrable acidity, the content of vitamin C and total amino acids decreasing, volatile aromatic compounds decreadsing abruptly. To preserve the intrinsic quality of litchi juice, in terms of the data detected in this research, not more than two concentrated times should be chosen. The optimized parameters were-0.088MPa of vacuum degree,152L/h of flow rate,56℃±2℃of steam temperature,concentrated twice, and the density of concentrated juice is32.61°Brix.The effects of ice-thawing concentration on the quality of litchi juice were researched. The results indicated that this concentrated method had the advantages of simple operation, and the total soluble solids and the browning degree in litchi juice were decreasing with thawing volume increasing. The particular volatile aromatic compounds of litchi juice in the course of concentration always existed. Taking all facts into consideration, the thawing litchi juice with40%of volume was found as the boundary point, with the ratio of40%of the concentrated juice and60%of the residual liquid. Rich volatile aromatic compounds can be found in the residual liquid and can be concentrated by other methods. With the method, we can get the litchi juice, by which the total soluble solid density can reach21.83°Brix.The effects of rotary evaporation on the quality of litchi juice were researched. The results indicated that this process needed less time to get the juice which had more condensed total soluble solids, but volatile aromatic compounds and nutrients were lost some. Comparing with general vacuum pump and high vacuum pump rotary evaporation, it can be figured out that the latter was better in color of the litchi juice and was close to the color of original one.Thus,High vacuum pump rotary evaporation is better than the general.The optimal conditions were-1×103Pa of vacuum degree,45℃of evaporation temperature,by which the total soluble solid density can reach45°Brix.Comparing the effects of six condition of concentration, including reduced pressure concentration, freeze-dry concentration, ice-thaw concentration, general vacuum pump rotary evaporation, high vacuum pump rotary evaporation and vacuum microwave dry concentration, on the quality of litchi juice. The results showed that nutrients in litchi juice can be preserved better under the condition of reduced pressure concentration, freeze-dry concentration and vacuum microwave dry concentration.Thermal processing methods,for example, rotary evaporation can lose the particular volatile aromatic compounds of litchi juice and the flavor compounds can be found in the distillate.Non-thermal processing methods can preserve the particular volatile aromatic compounds.For example, ice-thaw concentration can keep rich kinds and high content of volatile aromatic compounds. Taking volatile aromatic compounds into consideration, Non-thermal processing methods were better than thermal processing methods.Taking all factors into consideration,freeze-dry concentration and ice-thaw concentration are good methods to concentrate litchi juice.Freeze-dry concentration can preserve more nutrients,so freeze-dry concentration can be chosen as the best process to concentrate litchi juice.