Quantitative analysis of macro and micro-structure of gluten-free rice cakes containing different types of gums baked in different ovens Elif Turabi, Gulum Sumnu * , Serpil Sahin Department of Food Engineering, Middle East Technical University, 06531 Ankara, Turkey article info Article history: Received 21 January 2010 Accepted 2 April 2010 Keywords: Gums Image analysis Infrared Microwave Pore SEM abstract The effects of different gums on macro-structure of gluten-free rice cakes baked in conventional and infraredemicrowave (IReMW) combination ovens were investigated by using the images obtained by scanner and scanning electron microscopy in this study. The gum types used were xanthan, guar, locust bean, k-carrageenan and xanthaneguar blend. Cake containing no gum was used as control. It was observed that both addition of different types of gums affected the pore area fraction and percent number of pores of the rice cakes. The highest pore area fraction was obtained in cakes containing xanthan and xanthaneguar blend. Cakes baked in IReMW combination oven had higher porosity than those baked in conventional oven. Micro-structure of gluten-free rice cakes was also analyzed. According to these results, conventionally baked cakes showed more starch granule deformations. Both granular starch residues and deformed starch structure were observed together in cakes baked in IReMW combination oven. All of the starch granules did not lose their identity and did not disintegrate completely. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Celiac disease (gluten sensitive entropathy) is an intolerance to certain amino acid sequences found in the prolamin fraction of wheat (gliadin), rye (secalin) and barley (hordein). In genetically susceptible individuals, these kind of prolamins damage the mucosa of the small intestine leading to malabsorption of some nutrients. Until now, the only available treatment for celiac disease has been strict adherence to gluten-free diet and avoidance of gluten-containing foods. Since wheat is one of the main compo- nents of a daily diet worldwide, as well as the basic ingredient of most baked goods, a gluten-free diet is complex and can easily overwhelm patients (Kupper, 2005). Gluten replacement is nowa- days one of the most challenging issues for food science and technology since finding high quality gluten-free foods is one of the major issues for celiac disease sufferers. Rice containing no gluten, low levels of sodium, protein, fat and fibre, and a high amount of easily digested carbohydrates is desir- able for certain special diets (Ji, Zhu, Qian, & Zhou, 2007) such as gluten-free food products. However, due to its low gas retention capacity, rice products have some quality problems such as low volume, poor texture, color and crumb structure. Some food additives such as gums have been widely used in the gluten-free food formulations to overcome these problems. Gums act as poly- meric substances mimicking the viscoelastic properties of gluten in bread dough (Rojas, Rosell, & Benedito de Barber, 1999; Gomez, Ronda, Coballera, Blanco, & Rosell, 2007). Most of the studies in the literature are on the formulation of gluten-free breads. Studies on other gluten-free bakery products such as cakes, biscuits and pasta are limited. In the study of McCarthy, Gallagher, Gormley, Schober, and Arendt (2005), hydroxypropylmethylcellulose (HPMC) was added to a gluten-free bread formulation containing rice flour, potato starch and skim milk powder and response surface methodology (RSM) was applied for optimization of the formula- tion. Kang, Choi, and Choi (1997) showed that many gum types including HPMC, locust bean gum, guar gum, carrageenan, xanthan gum and agar resulted in acceptable rice breads. Cato, Rafael, Gan, and Small (2001) found that fine white and ground rice flours gave gluten-free breads of good quality when used in combination with CMC (0.8%) and HPMC (3.3%). In the study of Lazaridou, Duta, Papageorgiou, Belc, and Biliaderis (2007), the effects of different gums (pectin, carboxymethylcellulose (CMC), agarose, xanthan and oat b-glucan) on dough rheology and gluten-free bread quality were investigated. Microwave heating offers a new way of baking and brings a lot of advantages such as less start-up time, faster heating, energy effi- ciency, space savings, precise process control, selective heating, and food with high nutritional quality. On the other hand, microwave- * Corresponding author. Tel.: þ90 312 2105628; fax: þ90 312 2102767. E-mail address: gulum@metu.edu.tr (G. Sumnu). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2010.04.001 Food Hydrocolloids 24 (2010) 755e762