Preparation of low-fat uptake doughnut by dry particle coating technique

Soybean hull-wheat flour composites were prepared and used a doughnut formulation in order to decrease fat uptake during deep-fat frying. Soybean hulls were microparticulated by jet milling, and wheat flour was air-classified into coarse and fine fraction by an air classifying system. The coarse fraction of wheat flour was dry-coated with the microparticulated soybean hulls by a hybridization system. To investigate the effect on fat uptake, 4 different types of composites were prepared, which contained 0%, 1%, 5%, and 10% of soybean hulls. Doughnuts containing 1%, 5%, and 10% of microparticulated hulls decreased fat contents of 11.5%, 13.6%, and 35.8%, respectively. As soybean hulls content increased, hardness and crispiness increased. However, sensory evaluations demonstrated that there were no significant differences in appearance, flavor, crispiness, taste, and general liking (P < 0.05). Inner crust structures of doughnut showed slight reductions in cell size and improved cellular integrity with shrinkage in the cell membrane as the content of soybean hulls increased. These results show that microparticulated soybean hulls may form a protective layer during frying process, and this process could be used by the food industry for preparing doughnuts with reduced fat uptake.