Effect of Five Different Concentration Methods on the Quality of Litchi Juice
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Abstract:
In order to obtain high-quality concentrated litchi juice, the effects of 5 different concentration methods (vacuum concentration, freezing-thawing concentration, freezing concentration, secondary freeze concentration, primary freezing combined with vacuum concentration on the quality of concentrated juice were compared and analyzed. The results showed that the quality of the concentrated juice samples obtained by different concentration treatments differed significantly. Compared with the other concentration methods, vacuum concentration made the total phenol content being increased by 8.32%~21.17%, antioxidant capacity being increased by 2.38%~35.37%, particle size being decreased by 9.69%~48.69%, total color difference ΔE* value becoming the smallest, and stability becoming the highest. Compared with the other groups, the combination of primary freezing and vacuum concentration exhibited a synergistic bactericidal effect, causing the decreases in the total number of colonies and the number of molds, yeasts and lactic acid bacteria. The secondary freeze concentration led to the highest number of species type (32 kinds) and highest content (409.4 mg/L) of volatile substances as well as the highest content of geraniol (152.51 mg/L), with the least flavor loss. The results indicated that vacuum concentration, primary freezing combined with vacuum concentration and secondary freezing concentration had their respective advantages in protecting physicochemical quality, bactericidal effect and volatile profile of lychee juice. In view of the fact that the physico-chemical quality is an important index for evaluating the quality of fruit juice, while considering the highest efficiency and the lowest time cost of vacuum concentration, it is suggested that at present vacuum concentration can be used as a relatively suitable method to concentrate litchi juice. Further research on the coupling of vacuum concentration and freezing concentration can be carried out in the future in order to obtain a better concentration treatment mode.
