Masoud Najaf Najafi; Haminreza Shateri; Morteza Kashaninejad
Abstract
Introduction: It can be seen that in most studies published on low fat yogurt, the effects of fat substitutes or process changes, including the homogenization process, have been considered separately. However, process changes, especially changes in homogenization pressure, in addition to the effect on ...
Read More
Introduction: It can be seen that in most studies published on low fat yogurt, the effects of fat substitutes or process changes, including the homogenization process, have been considered separately. However, process changes, especially changes in homogenization pressure, in addition to the effect on yogurt, has also an effective role on fat substitutes such as hydrocolloids and can affect their functional characteristics. Therefore, in order to understand the proper conditions of industrial production, it is necessary to study these changes simultaneously. Due to the importance of low fat yogurt production, the effect of konjac gum, sage seed gum, homogenization rate and fat content on pH, texture, and color of low-fat yogurt was investigated using mixture-process variable experiments and modeling the properties obtained from this experimental method. Materials and methods: To prepare low-fat yogurt, firstly, the cream of 40% fat was added to the milk with 0.05% fat, sage seed gum, and konjac gum were added according to the design treatments and calculated by Pearson square method. The preparation was then heated to 90 °C and cooled down to 45 °C. The starter was then added and incubated in oven until reaching pH = 4.6. The yogurt was cooled down and dispersed in a 100 g cups of polyethylene. Texture analyzer was used for combination of back extrusion and texture profile analysis (TPA) test. The evaluated parameters were: hardness (N), cohesiveness, springiness, gumminess (N), chewiness (N), adhesiveness and adhesiveness force. pH was measured according to AOAC official method NO. 981.12. Results and discussions: The results showed that only the effect of fat content on the 99% level was significant on the pH of the samples, while konjac, sage seed gum, and homogenization rate had no significant effect. By increasing the fat content, the pH of the samples also significantly increased. It is likely that the increase in fat content will reduce the metabolic activity of the starter bacteria and thus increase the pH of the samples. Also, when the fat content of the samples was kept constant (1.75%), increasing the konjac gum and reducing the sage seed gum when the homogeneity of the samples was between 0 and 1200 rpm, the hardness of the samples initially increased and then decreased. When both gums were added at the same level, the hardness decreased indicating the high synergistic effect of these gums at low homogeneity rates. The results of this study showed that only linear effect of fat in 99% level on the adhesiveness force of samples was significant so that by increasing the fat content, the adhesiveness force of the samples increased. Also, the results showed that with increasing the konjac gum and reducing the sage seed gum, the gumminess of the samples first increased and then decreased. The most gumminess sample was in the conditions that both gums were used at the same level, indicating the high synergistic effect of these gums on the gumminess of the samples. The results of color measurement showed that only the linear effect of sage seed gum and the interaction effects of konjac gum-sage seed gum, konjac-gum on homogenization rates of L* samples were significant, and with increasing the level of konjac gum and reducing sage seed gum, L* samples decreased, but with increasing homogenization rates, L* samples increased. In this research, minimization of the fat content and adhesiveness force and maximization of the hardness and cohesiveness was considered as optimization aims. The optimum point calculated as 0.146% konjac gum, 0.053% sage seed gum, 2.42% fat content and 12300 rpm homogenization rate. In this conditio, the responses were: pH=4.5, hardness=3.25 N, adhesiveness force=0.815 N, cohesiveness 0.258 mm and L* 85/18. As a conclusion of this investigation, it could be said that these types of models could be utilized in industries to optimizing the formulation of such product, reducing the cost and increasing the acceptance.
