The purpose of this research is to study of the appropriate amount of purple sweet potato flour to substitute for wheat flour in brownies, which the percentages were  0 (controlled formula), 25, 50, 75 and 100. The study are found that the variation of the amount of purple sweet potato flour at different levels, ‘Aw’ values which is the free water activity ranged from 0.59 to 0.68, that is lower than the threshold of microbial  and bacteria required in its growth, moreover, the study results found that the amount of sweet potato flour does not affect to the values of L * and a * of brownies, but it affect to the values b *. With the evidence of yellow color, showing a yellow color lead to a decrease of the value b *, and this is found that the additions of purple sweet potato flour at the percentages of 25, 50, and 75, have the value b * more than the percentage of 100 with statistical significance at the 95% confidence level. With the textural analysis using a texture analyzer, the results of the verying amount of purple sweet potato flour found that when adding more purple sweet potato flour resulted in the Hardness, Chewiness, and Fracturability tend to increase. Due to the fact that purple sweet potato flour does not have gluten as the main component, as well as wheat flour, which gluten enable brownies to have textural properties that are soft and flexible. With the sensory quality evaluation of the variation of  the amounts of purple sweet potato flour to substitute for wheat flour by acceptance test method, used the liking 9 – Point Hedonic scale, the study found that the varying amount of puple sweet potato flour at 25% has the highest scores of the textural properties (softness) and the overall liking with statistical significance at the confidence levels of 95%. The chemical compositions of brownies maded from purple sweet potato flour contained total calories, carbohydrates, fat, moisture, protein, ash, fiber and anthocyanin, which are equal to 428.41 kcal, 12.43 g, 59.69 g18.37g, 6.03 g, 3.43 g, 5.91 g / 100g 2.11 mg / 100g, respectively. Thus, this study demonstates the feasibility in the use of purple sweet potato flour to substitute for wheat flour in brownies, as a result, this can increase the antioxidant activity.

Keywords: Brownies, Purple Sweet Potato Flour and Wheat Flour.