Abstract: The study data showed that the polyphenol oxidase (PPO) activity and browning degree (BD) of purple sweet potatoes peel are higher than those of inner-tissue and intact sweet potato. The relativity between them is positive, and relativity coefficient is 0.9895. Browning degree of fresh-cut purple sweet potato slice during storage period is found to be correlated with PPO activity. The activity of PPO extracted from purple sweet potato increases initially and decreases afterwards, with the highest activity of PPO on the third day. And BD increases very quickly as time going by, especially in the first three days. The relativity between PPO activity and BD is negative, and relativity coefficient is -0.8747.These results showed that the browning of purple sweet potatoes is mainly due to polyphenol oxidase in it.

Key words: purple sweet potato, polyphenol oxidase, PPO activity, browning degree