Rheological properties of gluten-free biscuit doughs containing tiger nut flour and quality properties of biscuits to be baked in infrared-microwave combination oven

Nowadays the most effective treatment of celiac disease is still the lifelong adherence to a gluten-free diet and also the use of nutritious and alternative sources to develop gluten-free food remains a popular topic in research. The aim of this study is to provide the use of gluten-free tiger nut flour which is not widely consumed in our country but rich in total dietary fiber and some minerals, for the production of gluten-free biscuits. The rheological properties of biscuit doughs containing tigernut flour at different ratios were investigated primarily. In addition, some physical, chemical and nutritional properties of biscuits baked in an infrared-microwave combination oven were determined and compared with conventionally baked biscuits in terms of quality characteristics. The biscuits obtained by mixing gluten-free tiger nut flour (TNF) and rice flour (RF) in certain percentages (0:100, 10:90, 20:80, 30:70, 40:60, 50:50) and containing xanthan gum were studied. According to the dynamic oscillatory measurements it was determined that the elastic modulus (G'), loss modulus (G'') and complex viscosity (ƞ*) values of the doughs were decreased significantly (p ≤ 0.05) when the TNF ratio was increased. Besides, as a result of creep and recovery measurements, it was determined that the maximum creep compliance value (Jmax) were increased with the increase in the TNF ratio. The biscuits were baked in infrared-microwave combination and conventional ovens. Different microwave and infrared heating powers and also baking times were tested to determine the effects of microwave and infrared heating on biscuit quality. Optimum baking conditions were 70% upper and lower halogen lamp powers, %20 microwave power and 3,75 minutes baking time. Conventional baking for comparing with infrared-microwave baking was performed at 130oC for 17 minutes. The physical and textural properties of the biscuits such as weight loss (%), width (mm), thickness (mm), spread ratio, hardness (N) and color values (L*, a*, b*, ∆E) were determined. The information about the nutritional value of the biscuits were obtained by performing total dietary fiber and mineral analyses (Ca, Mg and K). The weight loss value is generally found to be higher in the infrared-microwave combination oven than in the conventional oven. Furthermore, it was determined that the thickness and width increase in TNF biscuits were higher than control sample in both cooking methods. Addition of TNF to the biscuits increased the total dietary fiber and mineral content and resulted in high nutritious biscuits. It was concluded that the infrared-microwave combination method can be used as an alternative to the conventional method. Moreover, it was observed that infrared-microwave combination method decreased the baking time by 78% and gave the similar quality values as the biscuits baked by conventional oven.