Introduction: Fat substitutes are the compounds that use for providing all or some fat properties, while producing fewer calories than it. It is noteworthy that in confectionary products, carbohydrate-based fat substitutes are more used than other substitutes because of having other technical and economic benefits and one of these substitutes is gum. In this regard, in the present research, the effects of locust bean gum and xanthan gum as a fat substitute on the physicochemical, rheological and sensory properties of oil cake were studied.
Materials and Methods: Treatments included: A0 (control), A1 (0.2% (w/w%) xanthan and 0% locust), A2 (0.4% (w/w%) xanthan and 0% locust), A3 (0.6% (w/w%) xanthan and 0% locust) B1 (0.2% (w/w%) locust and 0% Xanthan), B2 (0.4% (w/w%) locust and 0% Xanthan), B3 (0.6% (w/w%) locust and 0% Xanthan), C1 (0.1% (w/w%) locust and 0.2% xanthan), C2 (0.2% (w/w%) locust, and 0.2% xanthan), C3 (0.3% (w/w%) locust, and 0.3% xanthan), D1 (0.4% (w/w%) locust, and 0.2% xanthan) and D2 (0.2% (w/w%) locust and 0.4% xanthan). In order to produce an oil cake, in the first step, the eggs, the sugar and emulsifier in the formulation were completely mixed by mixer with high speed for 3 minutes. In the second step, the oil and water were added to the mixture and mixed by the mixer with high speed. In the third step, flour, vanilla, baking powder, invert syrup and salt were added and mixed for 3 minutes at medium speed. In the fourth step, the dough obtained from the previous stage was poured into the desired molds and cooked in an oven at 175 o C for 30 minutes. Finally, the cakes were packed in polyethylene bags and stored at room temperature. The tests performed on the dough included the density, viscosity and specific weight, as well as tests on the final product included the measurement of moisture, aw, volume, color, fat, height and sensory tests. On the other hand, to evaluate the effect of xanthan gum and locust gum on cake texture, the test of firmness was performed on days 1, 7 and 15. In order to analyze the data obtained from the experiment (except for the instrumental analysis of data on the staling conducted by using a factorial experiment in a completely randomized block design), a completely randomized design with three replications was used and the mean comparisons were conducted by Duncan's multiple range test, at the probability level of α=1% and by SPSS software version 16.
Results and Discussion: According to the results, adding gum at different levels increased the viscosity of the dough samples compared to the control. The reason for the results is that the reaction between the gums and the protein of flour, especially gluten, leads to the strength of the gluten network and the increase in viscosity of the dough. According to the results, with the addition of different levels of gum, the density of dough decreased, some reasons of which can be water absorption and the amount of air bubbles in the dough. According to the results, by increasing gum content, the moisture content of cake samples increased due to the presence of hydroxyl groups in these compounds that form a hydrogen bonding with water, resulting in the stability of the gluten dough network, better preservation of dough water, reduction of the staling and firmness of the product. Also, by increasing the amount of gum, the fat content of the samples decreased. The reason for decreasing the fat in the cake samples containing the gum was to use them in the formulation of produced cakes instead of oil. On the other hand, the height of the cake is directly related to the volume of the samples, so that the height of the cake samples will be decreased by decreasing the volume, which it is consistent with the results obtained in this study. According to the results obtained in this study, when the amount of gum used in the product structure increased, the amount of fat decreased, and gradually the height of the desired cakes also increased. Then, the volume of samples increased by increasing gum content. The reason for increasing in volume of the samples containing gum is increasing the viscosity of the dough, slowing down the gas release rate, maintaining it in the early stages of cooking, and thus retaining CO2 and water vapor in the air cells. According to the results, the addition of gum increased the L * color index compared to the control sample. The reason for the increase of L* color index in gum-based treatments can be attributed to the dark color of gums, and on the other hand, to the reaction of becoming brown in the formulation of cake production. Adding the different gum levels also decreased a* color index. This is due to the moisture content in the crust, the intensity of the Maillard reaction, and the amount of light and bright colored compounds in the cake. According to the results, adding different gum levels decreased the b* color index in the treatments containing it. Also, increasing the levels of xanthan and Locust gum consumption decreased the staling of samples. According to the results, the addition of gums to the treatments increased the sensory scores of flavor due to the presence of aldehyde compounds in xanthan and locust gums. Addition of Locust bean and xanthan gums also increased the sensory score of color. The reason for this result can be attributed to the Maillard reaction. Overall, the addition of different levels of gums increased the total acceptance score of samples compared to the control sample, which can be attributed to the presence of xanthan and locust gums which have the special and proper work properties. Finally, according to the results, D2 treatment was introduced as the best treatment.