Optimizing the sensory properties and investigating the rheological properties of low-calorie dairy dessert containing sucralose-sorbitol sweetener with the D-optimal mixed design method

Dairy desserts are very popular among different age groups. There is about 10-12% sugar in the formulation of desserts and since sugar plays an important role in the taste, texture, color and other characteristics of food, removing or completely replacing them causes problems in the physico-chemical properties of the final product (McCain et al., 2018). In such products, a combination of low-calorie sweeteners can be used along with bulking agents to provide sensory and textural properties (Di Monaco et al., 2018). One of the most widely used sweeteners in low-calorie products is sucralose, which is derived from sugar, tastes very close to sucrose, is 6 times sweeter than sucrose, and has no aftertaste (Shankar et al., 2013). Due to the low molecular weight of sucralose, it is possible to use sorbitol, which is a 6-carbon sugar alcohol and is slowly metabolized in the body, to improve the textural and sensory characteristics of the dessert (Sheet et al., 2014). One of the statistical methods to minimize the number of trials is the D-optimal mixed design method, which was used to optimize the sensory characteristics and syneresis of the final dessert (Mannarswamy et al., 2010). The aim of this research was to investigate the use of a combination of sweeteners as a substitute for sucrose to achieve a low-calorie dairy dessert with optimized sensory and textural properties with the mixed design method. Finally, the rheological characteristics of the optimized dessert were compared to control dessert samples containing common sweeteners such as fructose, and some rheological models were fitted to predict the behavior of the optimized dessert.

In order to prepare the dessert, first all the fixed powder components including skim milk powder (2%), starch (3%) and kappa-carrageenan (0.5%) were combined together to prevent clumping and dissolve better. Then, using a Thermomix device, the powder components were dissolved in fat-free milk (71.5%) and 40% fat cream (10%) at a temperature of 10°C for 5 minutes, and after adding sweeteners (sweetening strength equivalent to 13 % of sugar) according to Table 1-2 were dissolved for 30 minutes at 350 rpm at a temperature of 45°C and finally pasteurized at a temperature of 73°C for 30 seconds and immediately packed in 100 gram containers and at a temperature of 4 °C were kept for 2 days. In order to prepare the sucralose-sorbitol sweetener solution (C), before the dessert production, different percentages of sucralose (from 0.005 to 0.06) were prepared in 20% sorbitol solution and the sample that had the sweetness equivalent of 20% sucrose solution was determined by sensory evaluation method and was used in this research. Then, according to Table 1 the formulations obtained from the experimental design were prepared then syneresis and sensory evaluation including texture, taste, aroma, appearance, sweetness and overall acceptance were performed. The rheological properties of the dessert samples were measured with a MCR-301 rheometer (Anton Paar GmbH, Graz, Austria) and a cone and plate probe with a diameter of 50 mm, an angle of 1 degree, and a gap distance of 0.05 mm.

The experimental design used in this study included three factors with two levels to investigate the relationship and effect of sucrose, fructose, sucralose-sorbitol sweeteners as independent variables on the obtained responses, including syneresis and sensory evaluation as dependent variables. was used (Table 1). The best fitted regression model, which was statistically significant (p<0.0001), was the Special cubic model for syneresis and the Quadratic model for other responses. Formulation optimization was done with the aim of the minimum percentage of sucrose, the minimum amount of syneresis, the best texture, taste, aroma, appearance, the most sweetness and the highest overall acceptance. The optimized formulation containing 9.2% sucrose, 9.3% fructose and 81.5% sucralose-sorbitol was obtained. According to the three-dimensional contour diagrams (Figure 1), the use of the combined sweetener sucralose-sorbitol in high amounts along with fructose syrup improves the textural properties. The graph related to other responses, increasing the concentration of C from low to high level leads to improvement of sensory evaluation results of taste, aroma, appearance, sweetness and overall acceptance. Therefore, it can be concluded that sucralose-sorbitol sweetener is a suitable substitute for sugar to be used in dairy desserts. Oscillatory and steady rheometric tests on 4 samples including dessert with 100% sucrose (sample 1), dessert containing 100% fructose (sample 2) and dessert containing 100% sucralose-sorbitol sweetener (sample 3) and optimized dessert (sample 4) was done. With the increase of shear rate, the apparent viscosity decreased in all samples, which indicates the non-Newtonian (pseudoplastic) behavior. The highest viscosity corresponds to the optimized sample. The effect of sweeteners on the rheological behavior of dessert was fitted well with Hershel–Bulkley, Cross, Carraeu models. Among them, the Cross model due to its high R2 (0.99) and low RMSE, can be a very suitable model for describing the rheological behavior in this research. The results of the investigation of thixotropic properties showed that the largest hysteresis loop area is related to sample number 4 and the lowest is related to sample number 3. Therefore, the presence of different sweetener has led to the production of desserts with higher viscosity but more thixotropic. For oscillatory rheological properties the linear viscoelastic region limit was determined as 1% strain by strain sweep analysis at 1 Hz frequency. We saw an increase in the values for the optimized sample, which indicated the positive effect of the optimized combination of sweeteners on the above parameters.

The design expert software and the D-optimal mixture design method were very efficient for designing the formulation of dairy desserts with alternative sweeteners in this research. Special cubic model for syneresis and Quadratic model for other responses of texture, taste, aroma, appearance, sweetness and overall acceptance were reported to be statistically significant. The composition of sugar substitute sweetener was obtained in the optimized formulation including 9.2% sucrose, 9.3% fructose and 81.5% sucralose-sorbitol. In order to check the rheological properties of the rheometric tests on the optimized dessert, the dessert containing 100% sucrose, the dessert containing 100% fructose sweetener and the dessert containing 100% sucralose-sorbitol sweetener were performed. The highest viscosity, the highest degree of pseudoplasticity was related to the optimized sample. Among the fitted models, Cross model is the most suitable model to describe the rheological behavior of dessert in this research due to the highest explanation coefficient (0.99) and the lowest RMSE. The results of oscillatory shear flow tests show the strong gel structure of the produced desserts.