Litchi pericarp browning is mainly induced by the enzymatic oxidation of phenolic substances. Usually blanching and pickling
treatments can effectively lower pericarp browning of litchis , including frozen stored litchis. This study also adopted these color-protectingtreatments before freezing. For quick frozen litchis, however, the mechanical injury of ice crystals on the pericarp will enhance the enzymatic oxidation due to the destruction of cell walls and therefore increased contact between phenolics, oxygen and enzymes which may be the reason for the increased browning observed in quick frozen litchis compared with fresh litchis. Thus, optimizing the freezing process to reduce mechanical damage to ice crystals could be another key measure to keep the natural color of frozen stored litchis. The analysis of color changes of frozen litchis (Fig. 4, IF vs. AF) over different storage periods demonstrated improved color retention in IF litchis, which
highlights the notable advantages of IF process in color protection. After frozen storage for 360 days, a* value and L* value of IF samples was similar to that of the fresh fruits, while after 60 days of storage,
the a* and L* values of AF samples decreased rapidly from 33/37 to levels of 23/28, respectively. The results indicate the desirable natural red color of litchi pericarp was well maintained in the IF process, which again showed that this novel process could have a promising industrial future.