An Alternative Frying Process for Wheat and Gluten-Free Donuts

by Melito, Helen Shirley

Abstract (Summary)
Fried foods are enjoyed worldwide as snacks or part of a meal. However, because these foods are deep-fried in oil, they tend to have a high fat content. Previous study on a partial- (par-) frying, infrared- (IR-) finishing process showed that French fries cooked by this process had significantly lower fat content than fully-fried French fries (13% vs. 19%, respectively, α=0.05). It was hypothesized that this par-frying, IR-finishing process would be able to produce donuts with a lower fat content but instrumentally and sensorially comparable to fully-fried donuts. Experiments were separated into three groups: wheat par-fried, IR-finished donuts, GF fully-fried donuts, and GF par-fried, IR-finished donuts. Four different formulations of GF donuts were tested, each formulation using a different combination of GF flours (commercial GF flour and rice flour) and hydrocolloids (pregelatinized rice flour and xanthan gum). Donuts were fried with and without a methylcellulose coating (0.5 g methylcellulose in 50 g water), which was brushed on before proofing. All of the par-fried, IR-finished donuts were par-fried for 64 s and finished in an IR oven. Two different IR cooking times (45 s or 53 s for wheat donuts, 39 s or 45 s for GF donuts) and four different distance combinations from the IR emitters to the food were tested. Mass, volume, and density changes, percent moisture and fat, crust color, and crust and crumb rheological properties of all donuts were compared to those of fully-fried wheat donuts. Sensory testing was also performed on selected donuts using a 9-point hedonic scale (1: dislike extremely, 9: like extremely) to measure overall acceptance, aroma, taste, and texture/mouthfeel. Statistical analysis (α=0.05) showed that all of the wheat par-fried, IR-finished donuts (25.6%-30.6%), most of the GF fully-fried donuts (26.3%-32.2%), and all of the GF par-fried, IR-finished donuts (23.7%-28.2%) had a significantly lower fat content than the wheat control (33.7%). Setting the emitters in either a height gradient from 45 mm to 25 mm or at a height of 35 mm above the top of the donut and using either IR time produced wheat par-fried, IR-finished donuts that were most instrumentally similar to the control, while using the same emitter settings and an IR-finishing time of 39 s produced GF par-fried, IR-finished donuts that were the most instrumentally similar to the control. Gluten-free fully-fried donuts made with a higher ratio of commercial GF flour to rice flour were more instrumentally similar to the control than donuts made with an equal ratio of commercial GF flour to rice flour, regardless of hydrocolloid used. Sensory scores of the wheat par-fried, IR-finished donuts (overall acceptance of 5.28-5.85) showed no significant differences from the control (5.83) with the exception of one slightly lower appearance score (5.69 for the par-fried, IR-finished donut versus 6.57 for the control). All GF fully-fried donuts (overall acceptance of 4.33-4.68) and all GF par-fried, IR-finished donuts (overall acceptance of 3.81-4.44) received significantly lower sensory scores than the wheat control (6.37 and 6.94, respectively). These results indicated that the GF donuts were not as well liked as the control, possibly due to their dryness. Overall, the par-frying, IR-finishing process was shown to significantly lower the fat content of both wheat and GF donuts while producing donuts instrumentally and sensorially comparable to fully-fried donuts made with the same formulation. This process may be used instead of a full-frying process to produce donuts instrumentally and sensorially similar to fully-fried donuts, but with a significantly lower fat content.
Bibliographical Information:

Advisor:Dr. Jonathan C. Allen; Dr. Christopher R. Daubert; Dr. Brian E. Farkas; Dr. MaryAnne Drake

School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:food science


Date of Publication:04/07/2009

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