study on physicochemical properties of gluten-free sponge cake

introduction: cakes are usually formulated including wheat flour, sugar, egg and some liquids such as milk, water and oil. the textural properties of gluten in dough such as tensile, expansion and tolerance capability during mixing are major factors in baking industry. in fact, the structural protein to produce bread, cakes, muffins and biscuits is called gluten and the absence of gluten due to production of bakery products caused delicate texture, poor color, low size and porosity. the use of gluten-free flours such as corn, potatoes and rice, millet, cassava, maize and sorghum in this category is inevitable. therefore, the use of gluten alternatives such as hydrocolloids, enzymes and proteins, are essential in providing this products. mtg is transferase enzyme that can be made connection between glutamine and lysine. result of this reaction improve nutritional and functional properties of the proteins. covalent links generated by mtg has unique effects on gelation capacity, thermal stability and water holding capacities of products. albumin and globulin do not have any effect on shaping of dough, but mtg connects the albumin and globulin to each other and then they become sedimented. this has beneficial effect on product quality. mtg has repairing ability on damaged wheat grains with binding protein. in this study, we try to contribute production of gluten-free sponge cake with guar gum, millet and rice flour, and mtg. materials and methods: tarom rice flour purchase from local market and keep refrigerated until use it. polyethylene bags with dimensions 15*25cm and thickness 40 microns were used. guar gum (meyprotm guar, e412), vanilla (rhovanilla of rodya company) and soy protein isolate (spi) was prepared from china. because of hygroscopic property of mtg, it was purchased in packages of 100 g, and stored at -15 ° c for further tests. for this purpose (0% millet-100% rice, 50%millet -50% rice, 100% millet-0%rice), guar gum (1, 2%) and mtg (0.25, 0.5%) were added. in order to increase the amino acid lysine as a substrate for the enzyme, soy protein isolate (spi) was added to mtg containing samples. after baking (170 °c, 20 min) and cooling, each of the samples packed in polyethylene bags to evaluate characteristics. moisture content base on standard aacc, 2000, measured. for size measuring, a piece of cake weighed and placed into the container with the specific volume (vt), the remaining space of container was filled with canola crops (vs) and then volume of cakes calculated (vt-vs). for evaluation of brain porous, cake was cubed in size 2*2 cm and scanned by the scanner with a resolution of 1200 pixels (model: hp scanjet g3010). statistical analyze base on factorial design were prepared in triplicate. duncan test at 5% level (p <0.05) were compared and the excel software was used for charts. results and discussion: results showed that different kinds of flour (rice and millet) have not significant effect on moisture content of samples but guar gum and enzyme have the ability to retain moisture during baking process. with increasing amount of enzyme and guar gum, volume of cake decreased. the study of the interaction of these three factors (rice-millet flour ratio, mtg and guar gum) showed that, sample with 50-50, rice-millet flour, 1% mtg and 0.25% guar gum has highest specific volume. with increasing amount of enzyme in cake, porosity significantly increased. however, increasing amount of guar gum did not have any significant effect on porosity (p<0.05). according to the results of the first stage, effect of different levels of rice and millet flour, mtg and guar gum on quantitative and qualitative properties of gluten-free sponge cake, it was determined that the sample contain 50% rice-50%millet flour, 0.25% mtg and 1% guar gum is best sample and it was compared with control sample (100% wheat flour) and cake without mtg. the result show that, guar gum, enzyme and composition of gluten free flour have ability to retain moisture, volume, porosity as well as control sample(100% wheat flour). conclusion: in the second stage, the best sample of the first phase (sample containing 50% rice-millet flour, 0.25% mtg and 1% guar gum) was compared with the sample containing 100% wheat flour and cake without mtg and confirmed that, statistically models have significant difference in 5% level.