Effects of Atmospheric and Vacuum Frying on the Quality of Donuts

In this study the differences in texture profile analysis (TPA), oil-uptake, and microstructure of donuts during atmospheric frying and vacuum frying (20 torr) were compared. Two types of donuts (cake donut and yeast-raised donut) with two temperature Levels (140℃ and 160℃) and three frying times (3, 4, and 5 minutes) were used for frying. Vacuum frying had a lower a-value on the surface of the cake donuts and formed larger pores and a rougher microstructures than the atmospheric deep-fried donuts. The L-value of the donut decreased with vacuum frying, and the hardness of the cake donut increased with both flying temperature and time. Scanning electron microscopy (SEM) of donuts under atmospheric frying showed various sizes of starch granules attached to the internal structure of the gas poles. There appeared to be fewer amount of starch in the cake donuts that were vacuum fried and their surface was smoother than that of donuts that were fried under atmospheric condition. The oil content of cake donuts was lower with vacuum flying than with atmospheric flying. However, the oil content of yeast-raised donuts was lower with atmospheric frying than with vacuum frying. In both types of donuts, the donuts deep-fried under atmospheric conditions at 140℃ for 5 minutes had higher sensory scores than any of the other processing conditions.