Effects of Sweet Potato Powder on Quality Characteristics and Antioxidant Activities of Rice Cookies

The physicochemical properties of rice cookie dough, including density, moisture content, spreadability, expansion rate, and loss rate, were analyzed after adding purple sweet potato powder at concentrations of 6%, 12%, 18%, and 24%. The color, hardness, staleness, antioxidant capacity, sensory attributes, and preference of the rice cookies were evaluated. The dough density decreased significantly as the levels of purple sweet potato powder increased, while the moisture content remained unaffected across samples. The spreadability, expansion rate, and loss rate exhibited significant reductions with higher purple sweet potato powder concentrations. Regarding the color characteristics of the cookies, the L* (lightness) and b* (yellowness) values decreased significantly, whereas the a* (redness) value increased as the purple sweet potato powder content increased. The cookie hardness increased proportionally with the amount of purple sweet potato powder added. The staleness patterns differed between the groups. The control and 6% and 12% groups displayed a gradual increase in staleness until day three, followed by stabilization, while the 18% and 24% groups experienced a rapid staleness increase until day two, with minimal changes thereafter. The content of total polyphenols, total flavonoids, total anthocyanins, and DPPH radical scavenging activity increased with the addition of purple sweet potato powder. According to the intensity evaluation of the sensory attributes, such as purple color, sweet potato flavor, sweetness, and hardness, increased as the amount of purple sweet potato powder added was increased. The appearance, color, flavor, taste, and overall acceptability were highest in the 18% and 24% groups without significant differences. Therefore, adding 18% to 24% purple sweet potato powder in the production of rice cookies is the optimal ratio that ensures high antioxidant activity while achieving high preference.