Effect of Hydrothermal/dry Heating and Particle Sizes of Rice Flour on Quality of Gluten-free Bread

Abstract

Introduction Due to the low amount of prolamin, rice flour is the most suitable raw material for preparing food for patients with celiac disease. Particle size classification and thermal treatments are among the physical methods to improve the functional characteristics of gluten-free flours and as a result, improve the quality of the products obtained from them. Particle size can increase the quality of gluten-free products by affecting the physicochemical properties of flour during hydration. Dry heat treatment and moist heat treatment are common techniques for physical modification which, depending on the intensity of temperature and storage time, lead to the improvement of gluten-free products by modifying starch grains, aroma, and flavor, and reducing microbial load. Considering that the effect of rice flour particle size on the quality of gluten-free bread has not been studied so far, in the current research, by dividing rice flour into particles with sizes of 180, 150, and 125 microns and using moist and dry heat treatments, The possibility of improving the functional characteristics of rice flour and improving the quality characteristics of gluten-free bread were investigated. Materials and Methods The content of moisture, pH, ash, and protein of rice flour was measured using AACC standard method (2000) and the total amount of starch was measured by the alkaline extraction method and the amount of starch damage was measured by non-enzymatic rapid method. To classify the size of the particles, waxy rice flour was divided by a shaker sieve with different sizes of 180, 150, and 125 microns, then under the influence of dry heat treatment for 2 hours and moist heat treatment with 25% humidity for 5 hours at a 110°C To produce gluten-free bread, the formulation used by Haghighat‐Kharazi (2020) was used with a slight change. Ingredients for gluten-free bread formulation for 100 grams of rice flour included 125 ml of water, 4.5 grams of sugar, 2 grams of salt, 6 grams of vegetable oil, 3 grams of yeast, and 2 grams of xanthan gum. Bread characteristics, which include weight loss, specific volume, oven spring, crumb crust ratio, shape index, porosity, crust and crumb color, and bread texture analysis were studied to evaluate the quality of bread. Finally, the factorial test was used to investigate the effects of particle size and heat treatment of rice flour, and Duncan's multiple range test was used to compare the means at the 5% probability level. Results and Discussions The results showed that the effect of particle size on weight loss, specific volume, oven spring, crumb to crust ratio, crust, and crumb color parameters, and bread texture was not significant (p>0.05). Regarding the sample volume index, C80 and DHT120 significantly had the lowest volume index (p<0.05). The HMT80-treated sample significantly increased the weight loss, and the moist heat-treated samples significantly increased the specific volume and the core to shell crumb (p<0.05). Sample treated with HMT 120 had the highest volume index. moist heat treatment and dry heat led to significantly decrease in brightness and an increase in the yellowness of the crust and crumb of the bread compared to the control sample, but there was no significant change in the amount of redness (p<0.05). Moist heat treatment samples had the lowest hardness and chewiness compared to the control sample and the dry heat treatment sample. In general, the sample obtained from 125-micron flour particle size and moist heat treatment led to the improvement of gluten-free bread quality.

Keywords

• celiace disease
• gluten-free bread
• physical modification
• waxy rice