Investigating the rheological properties and stability of Doogh containing chia seed mucilage

Introduction: Doogh is one of the native drinks of Iran and some other nations including Eastern Europe, the Middle East, Asia (Afghanistan, Azerbaijan, Armenia, Iraq, Syria, Georgia, and Turkey), and the Balkan Islands, whose consumption is It has a lot of history. According to the definition of Iran's national standard, simple doogh is a lactic drink obtained from milk fermentation, the dry matter of which is adjusted by diluting yogurt or milk in the doogh-making process. And due to the low pH, doogh is susceptible to contamination by molds and yeasts, and some bacteria, which causes the quality of doogh to decrease and its shelf life to decrease. Among the nutritional properties of doogh, we can mention the increase of vitamins and nutritious metabolites, the improvement of calcium absorption, and the digestibility compared to raw milk. Rheological behavior in macro and micro scales is one of the properties influencing the quality of food. Food flow behavior for a number of purposes such as quality control, as well as the final properties of the product such as stability, texture, and appearance, directly depends on the food microstructure. One of the major problems is the biphasic of doogh during storage, which is due to its low viscosity, low pH, and their effect on the precipitation of proteins. Types of stabilizers are used to increase the stability of the doogh product, which has satisfactory results. Hydrocolloids are widely used to create tissue stability in acid fermentation products. One of the significant issues in doogh is its consistency, which plays a very important role in its marketability. On the other hand, today, the desire of consumers to use natural antimicrobial substances such as chia seeds, which are considered a rich source of protein and dietary fiber, instead of chemical preservatives, has increased. Hydrocolloids are widely used to create texture stability in acid fermentation products. Chia seed with the scientific name Salvia hispanica L. is an annual summer plant belonging to the mint family. Chia seeds are considered as a rich source of protein (18-25%) and dietary fiber (20-37%). Also, chia seeds contain (21 to 33%) oil, of which (60 to 63%) is related to the essential fatty acid alpha-linolenic acid. These seeds also contain significant concentrations of natural antioxidants such as chlorogenic acid, caffeic acid, myristin, quercetin and kaempferol. Chia seeds contain large amounts of phytosterols that help prevent cardiovascular diseases and have anti-cancer, antioxidant, bactericidal and antifungal effects, which are excellent nutritional properties. The technological advantages of chia have led to its innovative use in food products. The concentration of mucilage, the amount of viscosity increases, and the highest and lowest levels of stability were observed in the samples containing 0.05% of mucilage (85%) and the control sample (52%), respectively.
Materials and methods: An optimization method was used to extract the mucilage of chia seeds. After dissolving the mucilage in deionized water, salt was added so that the amount of salt in the final product was 7%. In the next step, 40% of the doogh formulation was added to the stabilizer and salt mixture to prepare the doogh samples. Then, the effect of chia seed mucilage on the stability of doogh during 28 days of storage at 5°C refrigerator temperature was investigated. Chia seed mucilage was considered in a completely randomized design with treatments including concentrations of 0.01, 0.1, 0.3, 0.5% added to doogh and doogh without gum as a control sample. Then viscosity, zeta potential value, stability, sensory and chemical properties of doogh were measured. In this research, analysis and analysis of the results were done in the form of a completely random design and all the tests were done in 3 repetitions. To compare the mean of the treatments, Duncan's test was used using one-way analysis of variance (ANOVA) and SPSS version 16 software at a significance level of 0.05, and graphs were drawn using Excel software version 2016.
Results and discussion: Acidity and pH are one of the most important chemical factors in the stability and taste of doogh. The statistical analysis of the chemical analysis of doogh mixed with chia seed mucilage in comparison with the control sample after the preparation process shows that the Regarding the findings of this research, the acidity and pH of chia seed mucilage were investigated in the values of (0, 0.01, 0.1, 0.3 and 0.5 percent), the results show that the acidity of doogh samples is reduced with chia seed mucilage. But pH changes were not significant. The sample containing 0.5% chia mucilage had a higher apparent viscosity at low cutting rates than the control sample (without mucilage) and other samples. Also, this figure shows that the apparent viscosity of the doogh samples decreases with the increase of the shear speed, which in fact indicates non-Newtonian behavior (shear thinning). And in addition, it can be found that the degree of stability increased with the increase in mucilage concentration. Also, The evaluation of the obtained results does not show a significant difference between the sensory attributes of smell, taste, texture and mouthfeel (tenderness, uniformity or homogeneity, oral viscosity and mouth coating) and overall acceptance. The present study showed that in evaluating the mouth feel of doogh samples, no significant difference was observed between the samples and the control, because in addition to the oral viscosity, the uniformity and homogeneity of the samples were also considered. Therefore, it can be concluded that adding more than the appropriate amount of gum causes the samples to become undesired viscous and makes it unpleasant from the point of view of the consumer, because the presence of high amounts of hydrocolloid from the sample's psyche, which is one of the characteristics of desirability It reduces. In similar researches, the use of high amounts of hydrocolloids have been introduced as reducing the desirability and reported that depending on the type of hydrocolloid used, its appropriate amount to increase the consistency is different. The results also show that by increasing the concentration of chia seed gum compared to the control sample, the desirability of the consistency of the samples increases, but this effect decreases at a concentration of 0.5%. The results of the present study show that adding hydrocolloids to doogh causes the zeta potential of the doogh sample to become negative. Due to its anionic nature, chia seed gum has a negative zeta potential. Probably, chia seed mucilage as an anionic hydrocolloid has been absorbed on the surface of caseins and as a result, spatial and electrostatic repulsion has prevented the particles from approaching each other. Colloids containing particles with a low zeta potential (positive or negative), in the absence of other inhibiting factors such as high viscosity and spatial hindrance, will have a great ability to clot and aggregate. The larger numerical value of the zeta potential in the formulation containing gum means the presence of more repulsive force between the droplets and their less tendency to stick together, which in this case repels each other and makes the system stable. Therefore, by increasing the concentration of gum in the samples, the intensity of the charged ions of the samples increased. As a result, the spatial and electrostatic repulsion forces of these samples have shown an important role in stabilization. It could be obtained by increasing the concentration of mucilage, the amount of stability increased, so that there was a significant difference (P<0.05) between the samples and the control sample (without chia seed mucilage). The samples containing 0.3% and 0.5% concentration of chia seed mucilage resulted in 100% stability and the least stability (30%) related to the control treatment at the end of the 28th day. Our findings results are probably due to the polyelectrolyte nature of chia seed gum in 0.5% weight-volume solution; Because the chia seed gum polymer consists of carbohydrates with carboxyl and hydroxyl functional groups. It should also be added that chia seed mucilage did not change much in dry matter, fat and doogh protein content. And as the apparent viscosity of doogh samples containing chia seed mucilage shows, the sample containing 0.5% chia mucilage had a higher apparent viscosity than other samples, and the apparent viscosity of doogh samples decreased with increasing shear rate.
Conclusion: The results showed that the addition of chia seed mucilage up to a concentration of 0.1% on the 28th day of storage time resulted in a remarkable increase in the stability of doogh samples (62%), and concentrations of 0.3% and 0.5% resulted in complete stability of the samples. became The highest apparent viscosity in the samples containing chia seed mucilage is related to the concentration of 0.5 and then 0.3%. Since the highest consistency score in the sensory evaluation of doogh samples and its complete stability compared to the control sample was observed in the sample containing 0.3% chia seed mucilage, this concentration is suggested as the optimal concentration.