Effect of deep-oil frying on antioxidant properties of whole grain wheat donuts

Phenias Nsabimana

Deep-oil frying (DOF) consists of cooking food by immersing in edible oil at a temperature above the boiling point of water. Temperature may affect the nutritional quality of foods, including antioxidant capacity. Whole grain donuts formulation may be one option to improve the nutritional quality of donuts. The objective of the present study was to determine the effect of DOF on in vitro antioxidant properties of donuts prepared from soft white wheat flour, and soft winter and hard red whole grain wheat meals. Donuts were formulated and deep-oil fried (DOFd) at 1900C for 1, 2, 3, or 4min and at temperatures of 120, 140, 160, or 1800C. Donuts were analyzed for total phenolic content (TPC) and phenolic acid composition, DPPH radical and lipid peroxidation inhibition, and iron chelating capacity. Significant differences (P<0.05) between donuts DOFd for different lengths of time, and at different temperatures were recorded in TPC in all donuts. TPC increased by 112.2% for hard red whole grain wheat meal donuts (HRWGWMD), 83.5% for soft winter wheat flour donuts (SWWFD), and 72.5% for soft winter whole grain wheat meal donut (SWWGWMD); and decreased with further increase in frying time. TPC increased with DOF temperature from 120 to 180°C frying, by 73.7% for HRWGWMD, 59.4% for SWWFD, and 36.1% for SWWGWMD. Ferulic acid was the predominant phenolic acid in all donuts, followed by coumaric, vanillic, p-hydroxybenzoic, chlorogenic, catechuic, and caffeic acids. DPPH radical and iron scavenging capacities of DOFd donuts increased with time (from one to 3min) at 190°C, and temperature (from 120 to 180°C). Lipid peroxidation inhibition capacity of donuts increased up to 3min frying at 190°C, and decreased with extended frying in all donuts. Conversely, DOF at 120°C initially lowered lipid peroxidation inhibition capacity of all donuts. Consistent increase in lipid peroxidation inhibition capacity was observed with increase in frying temperature from 120 to 1800C. In conclusion, appropriate DOF time and temperature may increase the level and activity of antioxidants of foods. Hard wheat donuts showed lower volume and fat uptake, and future study may be needed to produce acceptable low fat donuts.

Effect of deep-oil frying on antioxidant properties of whole grain wheat donuts

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