Optimization of Cantaloupe pudding formula through replacing Spirulina platensis and stevia with milk powder and sugar using response surface methodology (RSM)

Milk dessert is a product that contains at least 50% the fresh cow milk or reconstituted milk, which is made with supplementary additives such as flavors, sweeteners, thickeners, and stabilizers, after undergoing heat treatment such as pasteurization or sterilization. Spirulina platensis is a multi-cellular microalgae and a green-blue filament that is a rich source of protein, essential amino acids, essential fatty acids, vitamins, minerals and pigments. Today, as a substitute for sucrose, non-caloric sweeteners are used, which in a small amount make too much sweetness, but they are not absorbed by the body. Of these, stevia with higher sweetness than sucrose (300 to 400 times), less calories and lower glycemia index, is a good herbal sweetener to replace sucrose.

Factor A contains the percentage of algae Spirulina platensis (alternative to milk powder) at 5 levels (0-2 % of the final formula), factor B contains the percentage of stevia replacement with sucrose at 5 levels (0-100), to achieve optimal pudding production formula were selected. Optimization of formula was performed based on the parameters of syneresis, viscosity, hardness and cohesiveness by Response Surface Method (central composite design, α=2 with 6 central points). The results were analyzed using SPSS 20 software and the comparison of the means was done by LSD at 5% level and the charts were drawn by Excel software.

Syneresis:
Generally, due to the increase of molecular connections between the chains and the outflow of water from the structure is created. According to the results of Table 3, the independent effect of stevia replacement with sugar, the interaction effect of Spirulina platensis and stevia replacement, and the quadratic effect of each of the independent variables on the Syneresis factor were significant (P <0.05). The rate of syneresis of the samples at higher levels of stevia replacement was reduced by decreasing the percentage of Spirulina platensis replacement, and at lower levels of stevia replacement, with the decrease in the percentage of Spirulina platensis replacement, the amount of syneresis significantly increased. Water holding capacity is linked to the ability of proteins, fats, and dietary fiber to maintain water inside the product structure. Because Spirulina platensis has high levels of protein, dietary fiber and fat, its presence in the formulation of frozen desserts has a significant effect on reducing the product's syneresis.
 
Viscosity:
As shown in Table 3, the independent effect of Spirulina platensis  replacement and stevia replacement, the interaction effect of Spirulina platensis  and stevia replacement, the quadratic effect of Spirulina platensis  and stevia replacement on the amount of viscosity was significant (P <0.05 ). The level of viscosity at lower levels of stevia replacement decreased with a decreasing percentage of Spirulina platensis replacement, and at the higher levels of stevia replacement, reducing Spirulina platensis replacement percentage was no significant effect on the viscosity (Fig. 2). In general, the presence of Spirulina platensis in the pudding formulation increased its viscosity, which could be due to the Spirulina platensis protein structure and intercellular interactions. Spirulina with high water absorption reduces water mobility. Also, the presence of fiber and hydroxyl compounds in the structure of this fine algae has a significant effect on the viscosity of the product.
 
 Hardness and cohesiveness:
Replacement of Spirulina platensis and Stevia in pudding formulations did not have a significant effect on the hardness and cohesiveness of texture. While the interaction effect of Spirulina platensis and Stevia replacement on the hardness and cohesiveness of the pudding samples was significant (P<0.001). The quadratic effect of Spirulina platensis and stevia replacement on the amount of hardness and cohesiveness of texture was significant (P <0.05). At lower levels of stevia replacement, by increasing the Spirulina platensis  replacement percentage, the hardness of the samples first increased and then decreased, while at higher levels of stevia replacement, with increasing Spirulina platensis  replacement percentage, the hardness of the samples first decreased and then increased. Large particles of Spirulina platensis can cause unconnectedness and network connectivity and ultimately create a more sophisticated structure. In fact, Spirulina platensis protein molecules, having a hydrophilic property, compete with other molecules to bind to water molecules, which results in a weaker and more unstable gel structure. On the other hand, tissue hardness is largely dependent on dry matter, the amount and type of protein in the sample. High levels of protein cause cross-linking in the gel network and, ultimately, a rigid and dense structure. But it should be noted that the amount of sample fat plays an important role in the product's texture. Since Spirulina platensis, in addition to protein, also has significant amounts of fat, the intervention of the fatty molecules of this small algae can be effective in forming a weaker gel network and producing soft texture in the product. Finally, optimal formula 1 (2 % Spirulina platensis and 95% Stevia replacement) and optimal formula 2 (0.1% Spirulina platensis and 50% Stevia replacement) were predicted.