Introduction: Chocolate is a complete and correct process of mixing one or more primary ingredients with the cocoa beans. These raw materials include the edible sweeteners or sugar, dry milk powder, edible essential oil and flavors as well as plant kernels. Despite high levels of fat and sugar, chocolate, has a significant contribution to human nutrition through the supply of antioxidants and polyphenols. It also has the beneficial minerals, especially potassium, magnesium, copper and iron. Milk chocolate is a complex rheological system that includes the solid phase (cocoa powder, sugar powder and no-fat dry milk powder) released in the continuous phase of cocoa butter. As mentioned, the chocolate contains three essential ingredients in foods, namely, protein, carbohydrate and fat, along with essential minerals that considering its physicochemical properties, the property of functionality can be activated in it by adding certain materials. The first member of omega-3 family is the alpha-linolenic acid that is not produced in the human body, hence it is called essential fatty acid and plays a very important role in many physiological responses of the human body and is considered as a necessity in the diet. The plant resources are healthier, cheaper, and more accessible. The highest amount of fatty acids, α-linolenic acid (short omega-3 chain), was found in plants. Among the plants, flaxseed has the highest fatty acid content (about 50%). Considering the above-mentioned cases, the possibility of producing the functional milk chocolate containing omega-3 fatty acid by this plant resource was investigated.
Materials and Methods: The treatments included control, L10, L20, L30 and L40 with the amounts of 0, 10, 20, 30 and 40% of flaxseed powder replacing butter, cocoa powder, dry milk and sugar. The experiments conducted included the study of physicochemical (sugar, fat, acidity, moisture content, peroxide, ash, particle size, texture and omega-3 levels) and sensory properties. In order to analyze the data of the research, a factorial experiment was used in a completely randomized design and the mean comparison was conducted by Duncan's multiple range test at the probability level of α =5%.
Results & discussion:The results obtained by studying the effect of adding flaxseed powder on the physicochemical properties, color, texture and sensory properties of functional milk chocolate showed that the addition of this material does not have a negative effect on the chemical properties of any treatment. The biggest concern was the oxidation of the oil in the flaxseed powder, which was solved with keeping conditions at 4 ° C and in none of the treatments the amount of peroxide did not increase more than the standard of chocolate (2%). On the other hand, the moisture content of the chocolate remained at the standard level due to the proper packaging and dry storage. Chocolate produced had a bitter taste in L30 and L40 treatments, despite having a good amount of sugar and dry milk powder, due to the relatively bitter taste of flaxseed oil and powder, but this bitterness was not so bad and unpleasant in L10 treatment. Chocolate acidity was not changed undesirably by adding flaxseed powder and replacing some of its oil with cocoa butter. Since the particle size of the flaxseed powder was more than that of cocoa powder and sugar, it reduced the volumetric surface, and fewer chemical bonds was formed between the hydrophilic and hydrophobic surfaces, resulting in less storage time of product at room temperature. Of course, this problem was less significant in L10 treatment, but in L30 and L40 treatments an inappropriate texture were found. The amount of omega-3 residues was zero in L10 and L20 treatments and was not detected by chromatography device, which indicated an inadequate ratio of antioxidant and flaxseed powder. However, since the maximum allowed antioxidants were used in chocolate, more amount of flaxseed should be used, so that as L30 and L40 treatment this fatty acid remains in the chocolate and does not oxidize. Also, by increasing the amount of flaxseed powder in treatments, viscosity also increased, due to the large size of particles and the lack of adequate bonding between hydrophilic and hydrophobic parts. Of course, this indicator was so high in L40 treatment that a problem was even created in molding. The texture analysis behavior of the chocolate indicated that the chocolate texture was loose in L40 treatment so that it lacked the value of production. The texture of this treatment was so loose that it became doughy at ambient temperature. In terms of sensory properties, a significant difference was found between the treatments and the control sample, indicating a decrease in the quality of chocolate produced. Overall, L40 treatment score was low due to so weak and doughy texture, inappropriate and bitter taste, the relatively dark color and the presence of many large pieces of flaxseed powder on chocolate. Therefore, its production does not seem logical, despite the proper amount of omega-3. L30 treatment had more desirable condition, but here, the texture was relatively loose too due to the presence of coarser flaxseeds. Of course, covering the bitter taste of flaxseed with sugar and dry milk powder and vanilla improved the opinion of the experts and increased their scores. It is noteworthy that the appearance and color of the product had better quality than L40 treatment. Regarding L10 and L20 treatments, although the scores of experts were better and they had better texture, color and flavor than two L30 and L40 treatments, but they did not have justifiable production due to the lack of remaining omega-3 in them that was the main purpose of this study. Totally, considering all properties, L30 treatment was introduced as the best treatment.