Antioxidant Activities and Phenolic Acids in Different Raw and Boiled Potatoes and Sweet Potatoes

Antioxidants have attracted great interests from food industries and scientists in recent years, because they have the capacity to reduce the harmful oxidation reaction in human body. Phenolic compounds are the common antioxidants that are widely found in fruits and vegetables. In this study, three varieties of potatoes and four varieties of sweet potatoes were used to examine the profiles and contents of phenolics in the raw and boiled potatoes and sweet potatoes. The Red Garnet Sweet Potato (RGSP) was the richest in phenolic content and selected to study the changes of free phenolics, total phenolic content, and antioxidant activity at different boiling times. In general, gallic acid and six different chlorogenic acid derivatives were found in the potatoes and sweet potatoes. The varieties of phenolic acids in the sweet potatoes were much more than the potatoes. The content of each phenolic acid varied in different raw potatoes and sweet potatoes. The total phenolics content of raw RGSP was the highest among these samples. A short time of boiling processing for potatoes and sweet potatoes could cause a significant increase in free phenolic acids, except 3-O-caffeoylquinic acid and 3,4-O-dicaffeoylquinic acid which were found to decrease during the processing. After boiled for 10 min, RGSP had higher level of phenolics and antioxidant activity than its raw or the one boiled for longer time. Therefore, the level of free phenolics and antioxidant activity in potatoes and sweet potatoes changed during boiling. They generally reached the peak level in a short boiling time (10 min) and then decreased with extended boiling time.