Purging fat from baked goods is always difficult because fat performs several functions in a recipe.
Fat makes baked goods tender by coating the proteins in flour and preventing them from joining together to form tough strands of gluten. Fat contributes to moistness and, when creamed with sugar, helps lighten and aerate the batter. And, as any expert baker can tell you, fat carries flavor.
Fruit puree can stand in for fat largely because the pectin and other soluble fibers it contains can also coat flour proteins. But without the flavor-enhancing presence of fat, the recipe must have some full-flavored ingredients so the taste of the final product is not overwhelmed by the puree. With this in mind, we chose a carrot cake with a rich spiciness for our puree experiment.
In the first round, we replaced all the vegetable oil with either prune puree or applesauce. Although our tasters found both oil-free cakes rubbery and the applesauce version bland, the stronger-tasting prune puree showed promise. Next we tested the recipe with a quarter of the oil in the original cake, substituting fruit puree for the rest. This time the prune flavor was undetectable and the cake was moist and pleasantly spicy. We improved the texture more by using cake flour in place of regular flour because cake flour is lower in gluten-forming proteins. With a few other fat-lowering strategies -- eliminating two egg yolks, halving the amount of walnuts and substituting low-fat cream cheese for butter and regular cream cheese -- the new carrot cake was delicious and contained less than a third of the fat of the original.
Reduced-fat carrot cake
1/4 cup walnuts
2 1/2 cups sifted cake flour
2 teaspoons cinnamon
2 teaspoons baking powder
1 1/2 teaspoons baking soda
1 teaspoon salt
2 large eggs
2 large egg whites
2 cups sugar
1 cup prune puree (see below)
1/3 cup vegetable oil
2 cups grated carrots (5-6 small carrots)
18-ounce can crushed pineapple, drained
12 ounces low-fat cream cheese, softened
1/2 cup confectioners' sugar
1 1/2 teaspoon pure vanilla extract
Heat oven to 350 degrees. Coat the inside of three 9-inch round cake pans with non-stick cooking spray. Line the bottoms with wax paper and set aside.
Spread walnuts in a pie plate and bake for 8 to 10 minutes, or until fragrant. Let cool and chop coarsely.
In a medium-sized bowl, stir together flour, cinnamon, baking powder, baking soda and salt. In a large bowl, whisk together eggs and egg whites. Add sugar, prune puree and oil and whisk until smooth. Add the flour mixture to the egg mixture and stir with a wooden spoon until blended. Stir in carrots, pineapple and the toasted walnuts. Divide the batter among the prepared pans and bake for 30 to 35 minutes, or until a cake tester inserted in the center comes out clean. Cool for 5 minutes in the pan on a rack. Loosen edges and invert cakes onto racks. Peel off paper and let cool completely.
For frosting, combine cream cheese, sugar and vanilla in a bowl and beat with electric mixer until smooth and creamy.
Place 1 cake layer on a serving plate. Spread with a scant 1/2 cup of the frosting. Add another layer and spread another scant 1/2 cup frosting. Place the third layer on top and spread with the remaining frosting.
To make prune puree, in a food processor, combine 1 cup pitted prunes with 6 tablespoons hot water; process until smooth. Makes 1 cup.