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 ...
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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.
Seyed Ali Mohammadi; Mohsen Ghods rohani; Masoud Najaf Najafi; Morteza Kashaninejad
Abstract
Introduction: In recent years, with increasing public awareness about the harmful effect of fat consumption, demand for low-fat dairy products has increased significantly. On the other hand, fat reduction reduces the rheological and sensory properties of food, such as taste, flavor, texture and mouth ...
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Introduction: In recent years, with increasing public awareness about the harmful effect of fat consumption, demand for low-fat dairy products has increased significantly. On the other hand, fat reduction reduces the rheological and sensory properties of food, such as taste, flavor, texture and mouth feel. Therefore, it is difficult to produce a low-fat product with the same characteristics of high-fat product. In order to imitate different functions of fat in low-fat foods, such as consistency of the product, mouth feel, color, flavor and rheological properties should be considered. Fat substitutes are macromolecules that are used to provide all or part of the fat functions in a food product and produce less calorie intake than fat. Konjac is a neutral and polysaccharide hydrocolloid that is used as a gelling agent in traditional Asian foods due to its high ability in absorbing water. In addition, it is one of the most viscous dietary fiber. The use of konjac in western countries is expanding as a component in functional foods. Konjac can therefore be used as an appropriate substitute for fat in dairy products such as cream, which in addition to reducing the amount of fat can maintain and even improve the physical and other properties of the product. The purpose of this study was to produce low-fat cream with good nutritional value, variety in formulation, as well as lower prices. Materials and methods: Fresh cream of 30% fat and pasteurized milk were purchased from Razavi Dairy Company and konjac gum was provided from Food Chem (China). First, the gum was mixed with the pasteurized milk at 45°C. Then the mixture was added to the cream of 30% fat to reach the fat content of 18– 25%. The final mixture, after homogenization in the different specified values of pressure, was pasteurized at 85°c for 15 min, and then packed in polyethylene bottles and kept in the refrigerator (4ºC) until theday of experiment. The effect of amounts of Kanjac gum (0.2- 0.6), the amount of fat (18- 25%) and homogenization pressure (100- 200 bar) on the sensory, color, and rheological characteristics of low-fat cream were investigated Results and discussions: The results of evaluating the characteristics measured using the response surface methodology indicated that the hardness, consistency, adhesiveness, b*, sensory score of texture, sensory score of aroma and overall acceptance of samples significantly increased with an increasing homogenization pressure. Also increasing fat content caused an increasing the adhesiveness, L*, b*, sensory score of taste, sensory score of aroma and total acceptance of samples. Increasing the konjac gum content also increased hardness, consistency, adhesiveness, and sensory score of texture. The distribution of responses in the principal component also showed that the instrumental measures like hardness and consistency were close to the sensory score of texture of the samples. This proximity of these attributes indicated that the properties measured by the panelists were approximately equivalent to the parameters which were measured by instrumental methods. Also, the results of the correlation coefficient between sensory and instrumental measurements showed that the highest correlation between hardness and sensory score of texture (a strong positive linear relationship (0.774), and between the consistency and sensory score of texture (a strong positive linear relationship (0.760)). Rheological and sensory properties in products such as cream, play an important role in the processing and marketability of the product. In cream, these characteristics are mainly influenced by the method of production, the amount of fat, and potential additives used. The results of this study showed that konjac gum as a hydrocolloid can be used as a proper substitute for fat in the cream, and with suitable sensory, color and rheological properties. The results of this study about the correlation between sensory properties and instrumental specification showed that the properties measured by the panelists are approximately equivalent to the parameters measured by the instrumental methods. Therefore, the results of instrumental methods in most cases can well predict the sensory properties of the cream and then can be replaced it.
Mostafa Kashaninejad; Masoud Najaf Najafi; Mohsen Ghods rohani; Morteza Kashaninejad
Abstract
Introduction: Labane or concentrated yoghurt is a semi-solid product which is being producedd by dehydration of yoghurt or separation of water and some water-soluble solids from yoghurt. High nutritional value, long shelf life, more desirable taste and texture and feasibility to produce other product ...
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Introduction: Labane or concentrated yoghurt is a semi-solid product which is being producedd by dehydration of yoghurt or separation of water and some water-soluble solids from yoghurt. High nutritional value, long shelf life, more desirable taste and texture and feasibility to produce other product are the reasons for high acceptance among customers. There are wide ranges of production methods from traditional methods which are tedious, such as separation of whey by fabric bags, to complicated time-consuming methods which also contaminate product and reduce its nutritional value. These cause demand to establish more suitable methods such as “wheyless process” by dried milk, concentrated milk protein or concentrated whey protein. On the other hand, one of the methods for enhancing firmness and textural properties of yoghurts, similar to other dairy products is utilization of hydrocolloids. These components are used for enhancing rheological an textural properties of food and commonly used as additives for increasing viscosity, gel forming ability, enhancing physical stability, film forming ability, controlling crystallization, postponing syneresis and textural improvement. Konjac gum (KG) is a neutral polysaccharide that derived from Amorphophallus konjac C. Koch tuber, which is well known in east countries during centuries. Ability to hold water and reduction of cholesterol and glucose are the reasons for grossing demand of this gum. So due to the importance of labane produced through wheyless process, the effect of different ingredients of formulation such as milk protein concentrate, cheese whey powder and konjac gum on physicochemical, rheological and sensory properties of labane was investigated and compared these properties by using Principal component analysis (PCA) and Partial least squares regression (PLS regression). Materials and methods: Cow milk was purchased from local market (Mashhad, Iran). Dried skim milk, milk protein concentrate, cheese whey powder and commercial starter provided from Khorasan Razavi Pegah Company (ABY1, Christian Hansen, Horsholm, Denmark) and KG purchased from Food Chem. (China). In order to concentrate the milk, 3% dried skim milk was added to1 Kg milk. Then, according to the experimental design (table 2), MPC and CWP added to milk at 0, 4, 6 and 8% levels which reached the total solid of milk to 21.5%. KG with percentage of 0, 0.05, 0.1, 0.15, and 0.2% was added to the mixture at 40˚C. The mixtures were homogenized at 50˚C and pasteurized at 90˚C for 1 min. and then cooled to 43-45˚C. The mixtures were incubated at 43-45˚C for 3-4 hours after addition of starter. Then the samples were slowly stirred and packed in polyethylene bags after reaching to suitable pH. The samples were transfered to refrigerator for 24 hours then the tests were conducted. PH was measured according to AOAC 2005 official method NO. 935.42.25 gr of samples were centrifuged at 4˚C for 10 min. at 4500 rpm. Syneresis was evaluated as parentage of separated serum. Texture analyzer was used for combination of back extrusion and texture profile analysis (TPA) test. 50 mm in diameter cylinder with 10 mm in height and probe with 4 mm diameter and 100 mm height with the speed of 1 mm/s were used to conduct the test. Dynamic rheological parameters were evaluated by rheometer (Parphysica). The devise was equipped by 50mm diameter parallel plate with 2 mm gap. Eheo plus/32 version V3.40 software was used to measure elastic modulus (G’), loss modulus (G”) and η*. Results & discussion: Results showed that none of the linear, quadratic and interaction effect of MPC, CWP and KG was significant on pH of the samples at the first day. Results represented that the pH of the samples was varied from 0.36 to 0.94 after 5 days and only linear effect of MPC and CWP (at 99% level of confidence) and interaction effect of CWP-KG (at 95% level of confidence) were significant on that. The effect of MPC and CWP and interaction effect of MPC-KG, CWP-KG and CWP-MPC-KG were significant on syneresis at 99% of confidence. Results showed that hardness of the samples varied between 3.25-9.58 N and the interaction effects of MPC-KG, CWP-KG and CWP-MPC-KG were significant at 99% of confidence. None of the linear, quadratic and interaction effect of CWP, MPC and KG was not significant on springiness of the samples (p>0.05). In strain sweep test, two separated regions were distinguishable: linear viscoelastic (LVE) region that elastic and viscous modulus (G’ and G”) were constant and G’ was higher than G” which showed the solid like behavior, and non-LVE region that G’ and G” decreased by increasing strain and led to a crossover point (flowing point) which G” goes over the G’ and liquid-like behavior shows itself. In this test, strain corresponding to start of the non-LVE region and sharp reduction of G’ define as critical strain (γc) and the corresponding stress of this point defined as critical stress (τc).Results represented that G’LVE and G” LVE of the samples varied from 22.54 to 750.1 and 11.01 to 242.1 Pa, respectively and the selected model (cubic x quadratic) showed that the interaction effect of MPC-KG, CWP-KG and CWP-MPC-KG on G’LVE and G” LVE was significant at 99% of confidence while the interaction effect of CWP-MPC was only meaningful on G” LVE. Results also showed that the variation trend of G’LVE and G” LVE was the same by alteration MPC, CWP and KG in a way that both of these parameters were increased by increasing KG. The effect of MPC-KG and CWP-KG was significant on γc and τc at 95% confidence and also, in addition to mentioned effect, the interaction effect of CWP-MPC was significant only on γc. Increasing KG increased γc at higher amount of CWP and lower amount MPC which can be concluded that increasing KG amplified the gel strength. Also, the results of the correlation study between sensory and instrumental measures showed that there was a close relationship between the score of sour taste and the overall acceptance of samples, which showed that among the measured characteristics, sour taste score is more important than other parameters.
