Kwame was testing for the food group of simple carbohydrates, specifically reducing sugars, in the orange juice using Benedict's solution. Benedict's solution is used to detect the presence of reducing sugars, which include monosaccharides and some disaccharides. When heated with a reducing sugar, Benedict's solution changes color from blue to green, yellow, orange, or brick red depending on the amount of sugar present, indicating a positive test for these sugars.