Effects of deep-fat frying temperature on antioxidant properties of whole wheat doughnuts

Authors: NSABIMANA, PHENIAS - Washington State University; POWERS, JOSEPH - Washington State University; MATTINSON, SCOTT - Washington State University; Baik, Byung-Kee

Submitted to: International Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2017
Publication Date: 10/30/2017
Citation: Nsabimana, P., Powers, J.R., Mattinson, S., Baik, B.V. 2017. Effects of deep-fat frying temperature on antioxidant properties of whole wheat doughnuts. International Journal of Food Science and Technology. 53(3):665-675. https://doi:10.1111/ijfs.13641.
DOI: https://doi.org/10.1111/ijfs.13641

Interpretive Summary: Donuts are deep-oil fried wheat food products popularly consumed throughout the world, largely owing to their attractive sensory properties such as color, flavor, texture and palatability which result from being cooked in oil at a high temperature for a short time. High temperature deep-oil frying could influence the nutritional quality of foods and oxidation of the absorbed oil during preparation and also storage. Using whole grain meals of a hard and a soft wheat, and a refined soft wheat flour, we investigated the effects of deep-oil frying temperature on the product quality, phenolic compound content, phenolic acid composition and antioxidant capacity of donuts. The color, volume, phenolic compound content and antioxidant activity of donuts were all significantly affected by frying temperature. An elevation of the frying temperature reduced the required frying time, moisture content, volume, oil absorption and brightness of donuts, but produced donuts with a firmer texture. Initial deep-oil frying considerably reduced the phenolic content of donuts, but as the frying temperature increased, increases in phenolic content and antioxidant activities of donuts (determined by radical and lipid peroxidation inhibition activities) were observed. Hard red wheat whole grain meal donuts were smaller, darker and harder, but lower in fat absorption and higher in phenolic content, than soft white wheat whole grain meal donuts. A high frying temperature is desirable for increased phenolic content and antioxidant activities, whereas a low frying temperature is advantageous for the production of donuts with high volume, soft texture and brighter color, indicating that an intermediate frying temperature would be appropriate for the production of donuts possessing both acceptable sensory attributes and high antioxidant activities.

Technical Abstract: The total phenolic content (TPC), phenolic acid composition, and in vitro antioxidant capacity of whole wheat donuts fried at 120, 140, 160, or 180'C were determined and compared in two types of wheat to identify the effects of frying temperature. Significant differences (P<0.05) in TPC were observed between donuts fried at different temperatures. The TPC of donuts decreased first significantly when donuts were deep-oil fried at 120°C, from 0.91, 1.31 and 1.87 to 0.32, 0.72 and 0.76 mgGAE/g for soft white wheat flour donut (SFD), soft white whole grain wheat donut (SWD) and hard red whole grain wheat meal (HWD) respectively. Then, the TPC increased with elevation of frying temperatures from 120 to 180°C, from 0.32, 0.72 and 0.76 to 0.51, 0.98 and 1.32 mgGAE/g for SFD, SWD, and HWD, respectively. These increases in TPC of donuts were also detected in the determination of individual phenolic compound using a HPLC. DPPH radical and iron chelating capacity of deep-oil fried donuts exhibited increases with elevation of frying temperature from120 to 180°C. Deep-oil frying at 120°C initially lowered lipid peroxidation inhibition capacity of donuts prepared from both refined flour and whole grain meals, and increased consistently with increased frying temperature from120 to 180'C. These results showed that moderate deep-oil frying temperature would increase the content and activity of antioxidants of donuts.