Abstract: The main purpose of this study was to improve the function and quality of frozen purple sweet potato cubes. In this study, osmotic dehydration (OD), natural drying, hot air drying and freeze drying (FD) were used as pretreatment methods to evaluate the changes in anthocyanin composition of purple sweet potato after freezing and thawing, and to identify the most effective pretreatment methods to reduce the loss of anthocyanin in the freeze-thawing process. The results showed that after freezing and thawing, OD-treated purple sweet potato exhibited a significant decrease in total colordifference compared with the other pretreatment groups (P < 0.05), and the colour was closest to that of the fresh samples. Compared with other treatment groups, OD and FD pretreatment could significantly inhibit the polyphenol oxidase (PPO) and peroxidase (POD) activities of purple sweet potato after dehydration (P < 0.05), while the OD-treated group had the lowest PPO and POD activities. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging capacity and total antioxidant capacity were maintained at a higher level in the OD- and FD-treated groups compared to the other pretreatment groups. Twenty-seven Anthocyanins in purple sweet potato were lost after freezing and thawing. Compared with other pretreatments, OD pretreatment minimised the loss of anthocyanins after dehydration and freeze-thawing of purple potato cubes. Therefore, OD is the most effective pretreatment method for anthocyanin protection infrozen purple sweet potato, which is suitable for freezing storage of purple sweet potato to be used for anthocyanin extraction.

Key words: purple sweet potato; dehydration pretreatment; freezing; thawing; anthocyanin loss