Thesis Type: Doctorate
Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Food Engineering, Turkey
Approval Date: 2013
Student: İLKEM DEMİRKESEN MERT
Co-Supervisor: SERPİL ŞAHİN, SERVET GÜLÜM ŞÜMNÜAbstract:
The main objective of this study was to formulate gluten free breads based on different flours, gums, and emulsifiers for baking in infrared-microwave combination oven. In the first part of the study, the rheological properties of different gluten-free bread dough formulations containing only rice flour and rice-chestnut flour blend with different gums, gum blends and/or emulsifiers were evaluated. Power law model and Herschel–Bulkley models were found to explain the flow behaviors of rice and chestnut-rice dough formulations, respectively. The formulations with the chestnut:rice flour ratio of 30:70 promoted the desired quality parameters of gluten-free breads. Using tigernut flour in formulations improved the color of gluten-free rice breads. Furthermore, gum blend and emulsifier DATEM addition were found to be the necessary ingredients to obtain the desired physical properties in gluten-free bread formulations. In the second part of the study, Response Surface Methodology (RSM) was used to optimize formulations and infrared-microwave baking conditions for gluten-free breads. Breads containing 46.5% chestnut flour and 0.62% emulsifier and baked using 40% infrared and 30% microwave power for 9 min had comparable quality with conventionally baked ones. The effects of different flours, gums, and emulsifiers on macro- and micro-structures of the gluten-free breads baked in different ovens were studied by using image analysis technique and Scanning Electron Microscope (SEM). The highest pore area fraction values were obtained in breads prepared by replacement of 46% of rice flour with chestnut flour containing xanthan–guar gum blend–DATEM mixture and baked in an infrared–microwave combination oven. The addition of different gums and gum blends on the crumb structures of gluten-free breads were evaluated by using X-ray microtomography (X-ray μCT) and gluten-free breads prepared with the addition of xanthan, carboxyl methyl cellulose (CMC), xanthan-guar, xanthan-LBG and HPMC had higher number of smaller pores with finer crumb structure. Lastly, the effects of different formulations and storage time on staling of conventionally and infrared-microwave baked breads were studied. Firmness, moisture loss and retrogradation enthalpy values for all bread samples increased significantly during storage. Retrogradation enthalpies and total crystallinity values of breads did not show significant differences with baking method. Using chestnut flour and xanthan-guar gum blend-DATEM mixture in formulations significantly delayed staling of gluten-free breads by decreasing moisture loss, firmness, retrogradation enthalpy, and total mass crystallinity.