Optimization of Non-dairy Dessert Formulation based on Almond Milk Containing Tragacanth Gum and Stevia Sweetener

Introduction  The demand for non-dairy and reduced-calorie products has increased substantially for several reasons. Almond (Prunus dulcis) milk is highly appreciated by lactose-intolerant, hypertensive people and celiac patients whom are not able to consume animal's milk. Thus, the development of various non-dairy products is essential. Desserts are the most common and popular product containing high amount of fat and sucrose. The consumption of sucrose is restricted for diabetic people due to its high glycemic index. Stevia as a low-calorie sweetener is one of the sucrose substitutes in food products. Sucrose substitutes must mimic the techno-functional properties of sucrose. Generally, commercially available sucrose substitutes do not possess all of the required characteristics. Therefore, using them in blend form with sucrose is suggested. Moreover, sucrose replacement especially in desserts generates a negative effect due to low firmness or higher syneresis. In this regard, hydrocolloids can be used to overcome those drawbacks. Therefore, the current study was carried out to investigate and optimize the non-dairy dessert formulation based on almond milk containing Tragacanth gum and stevia. For this purpose, the effect of Tragacanth gum and stevia as a sucrose replacer on the physicochemical properties such as hardness, viscosity, color coordinates including lightness, redness-greenness (a*), yellowness-blueness (b*), total soluble solids and syneresis was evaluated and optimized using Response Surface Methodology (RSM). Materials and Methods  All of the materials used for the manufacturing of non-dairy dessert including raw almond, stevia and Tragacanth gum were purchased from a local market of Zanjan, Iran. For the production of non-dairy dessert, the almond milk warmed up to 40 ºC and then stevia as a sucrose substitutes and tragacanth gum powder as a stabilizer were added in the ranges of 25-75% and 0.4-1% w/w, respectively. Later, the temperature of the mixture increased to 72 ºC and kept for 10 min and then, the temperature decreased to 42 ºC to inoculate the starter culture (a mixture of Streptococcus thermophilus and Lactobacillus bulgaricus, 2% w/w). The fermentation process was completed at 37 °C for 24 h. Finally, the temperature of non-dairy dessert based on almond milk was decreased to 4ºC and kept at the same temperature until further analysis. The pH of the desserts was measured using a pH meter model AZ 86502 (AZ, Taiwan). Total soluble of the desserts was determined using a refractometer (ATAGO, Japan). Firmness was determined using a STM-5 texture analyzer (SANTAM Co., Iran) equipped with a 20 Kg load cell and 10 mm probe. Viscosity was measured using a programmable Viscometer (R/S-CPS+, Brookfield, USA) equipped with a cone-plate geometry at shear rate of 100 s−1. Instrumental color measurement was carried out by a handheld colorimeter (TES135-A, Taiwan) considering L*, a* and b* as color coordinates. Syneresis was measured by a centrifugation test. Fifteen semi-trained panelists (7 male and 8 female) were selected to evaluate sensory properties of the control (only contains sucrose) and optimized formulation samples for texture, color, appearance, taste, flavor, total acceptance using a 5-point Hedonic scale (1= dislike extremely and 5=like extremely). The RSM-central composite design was used to build up the experimental design and identify the conditions that yield highest firmness, viscosity, L*, and total soluble solids as well as lowest a*, b* and syneresis. Results and Discussion  The results obtained revealed that the hardness, viscosity, a* and total soluble solids increased significantly (p<0.05) while the lightness, b* and syneresis decreased significantly (p<0.05) with increasing the Tragacanth gum in the formulation of non-dairy dessert based on almond milk. In addition, increasing the replacement of sucrose with stevia significantly (p<0.05) reduced the hardness, viscosity, total soluble solids, and increasing lightness and syneresis. However, increasing the percentage of sucrose replacement with stevia had no significant effect (p>0.05) on the changes of a* and b*. Optimization of non-dairy dessert formulation based on almond milk was carried out using numerical technique. The optimal formula was 1% Tragacanth gum and 45% replacement of sucrose with stevia. Under these conditions, hardness 0.08 N, viscosity 1.20 Pa.s, lightness 82.77, redness-greenness 0.95, yellowness-blueness 5.60, total soluble solids 8.29 ºBrix and syneresis 11.88% were obtained. The results of sensory evaluation showed that addition of Tragacanth gum and replacing stevia at the optimal levels improved the total acceptance score compared to the control sample. It can be concluded that in addition to the reliability of the RSM to select the optimal formulation conditions, Tragacanth gum and stevia can be used to produce a new, reduced-calorie and customer-friendly non-dairy dessert based on almond milk.