Document Type : Research Article
Authors
Department of Food Science and Technology, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran
Abstract
Introduction
Ice cream is a frozen product, which is obtained from milk by adding compounds such as sweeteners, emulsifiers, stabilizers and flavoring agents. The structure of ice cream is a complex physicochemical system composed of three phases: liquid, solid and gas. Scientific results have shown that there is a connection between high fat consumption and cardiovascular diseases. Considering that ice cream is an almost fatty product and is particularly popular among people in the society, there is a greater demand for consuming low-fat varieties of this product. The food industry is also looking for new alternatives to minimize the negative effects of fat reduction on quality of ice cream. Hydrocolloids, are carbohydrate-based fat substitutes, which can mimic the mouthfeel and flow characteristics of fat cells due to their emulsifying and water binding capabilities. Eremurus luteus is one of the rhizome plants belonging to the Asphodelaceae family, cultivated around the world, including Iran. Cerise root gum is a new source of hydrocolloid with a glucose to mannose ratio of 1:1 to 1 from the family of glucomannans. The intrinsic viscosity of this gum was measured as 6.32 and 6.35 dl/g according to Huggins and Kramer equations, respectively, and it has the highest foam stability in concentrations of 0.2 to 0.5%. The rheological properties of cerise root gum have proven its important role as a new thickener, stabilizer and foaming agent.
Materials and Methods
In this research, sterilized and homogenized milk (1.5% fat) from Mihan Dairy Industries Company, sterilized and homogenized cream (25% fat) from Pegah Khorasan Dairy Industries Company, emulsifier 471 E from Beldom Belgium Company, powdered skim milk from Pegah company.Sugar and vanilla from confectionery store. Serish root gum was prepared according to the method of Salahi et al. (2020).
The amount of ingredients required for the normal sample (high-fat control) was determined based on primary sources, including 10% fat, 11% fat-free milk solids, 12% sugar, 0.25% stabilizer, 0.15% emulsifier and 0.1% vanilla. According to the definitions for reduced-fat ice cream, 75% fat reduction was made from the normal sample (10% fat). In this regard, the investigated treatments were as follow: the amount of fat (2.5% fat: L), the type of gum (SRG) and the concentration of gum (at four levels: 0.2, 0.3, 0.4, 0.5%) compared to the control sample as high fat (10% fat: F).
First, the liquid ingredients, including milk and cream, were continuously stirred while heating up to a maximum of 5 °C. After that, the mixture of solid materials (sugar, milk powder, gum, etc.) was added to the liquid part and mixed with a stirrer for three minutes after dissolving thes solids. The resulting mixture was pasteurized at 80°C for 25 seconds and homogenized with a homogenizer at 22,000 rpm for 1 minute and transferred to a water, salt, and ice bath and cooled to 50°C. Then, it was kept in the refrigerator at a temperature of 5°C for 24 hours. Finally, the mixture was transferred to a non-continuous ice cream machine for 15 minutes for the freezing stage, and the samples were poured into special containers with lids and coded, and placed in a freezer at -18 °C for at least 24 hours.
Results and Discussion
By adding gum and increasing its concentration, the amount of apparent viscosity, consistency coefficient, yield stress, plastic viscosity, textural characteristics (hardness, adhesion, continuity and apparent modulus of elasticity) increased. In the sensory evaluation section, the characteristics of creaminess, sweetness, viscosity, roughness, coldness and hardness were evaluated by transient dominant sensation test and these changes were significant in most cases. Sample containing 0.3% gum had the highest overall acceptance after the control sample compared to other samples. The results showed that these variables have the ability to simulate rheological properties (apparent viscosity, consistency coefficient, yield stress and plastic viscosity), melting speed and sensory characteristics such as creaminess, roughness, cryogenicity, viscosity, hardness and overall acceptance of the control sample with high fat as effective factors on the texture production process and the mouthfeel of the product in low-fat ice creams. On the other hand, due to the absence of significant differences between the data obtained from the pH and dry matter measurement tests, the applicability of Serish gum can be confirmed as a fat substitute.
Conclusion
The examined samples all showed the loosening behavior with cutting. In the sample containing 0.2% gum, the melting speed increased (from 0.32 to 0.39), also with the increase in the amount of gum in the samples, the freezing temperature decreased by one degree Celsius (from39.4 to 39.5). Overall acceptance, pH and dry matter did not change significantly, which indicates the usefulness and applicability of this method. Also, regarding the rheological characteristics, the highest consistency coefficient in the 0.5% gum sample was 2.2605, similarly, the highest yield stress was in 0.5% gum sample and was 6.7076 pa. Similarly, the highest amount of Plastic viscosity and apparent viscosity belonged to the sample containing 0.5% gum. It was also shown that in the rheological characteristics, with the increase in the amount of gum in the samples, the amount of the relevant parameter increased significantly, and in all these parameters, sample containing 0.2% showed a lower amount than the control sample.
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