Document Type : Full Research Paper
Authors
Department of Food Science and Technology, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
Abstract
Introduction: Ice cream contains a mixture of milk components, sweeteners, stabilizers, emulsifiers, and flavorings. The quality of the finished product depends not only on the processing conditions or the freezing efficiency, but also on the constituents, the amount of entrapped air, and the number of ice crystals. The physical structure of ice cream has a significant effect on the melting properties (melting rate) and texture (hardness) of ice cream (Mouse & Hartel, 2004). The improvement and expansion of the ice cream structure are attributed to the macromolecules present in the ice cream mixture; milk fat, protein, and carbohydrates (Adapa et al., 2000). Quinoa as a high biologically valuable protein can be used in various food products to enrich and positively affect the physical and sensory properties of the product (James, 2009). The purpose of the present study was to replace skim milk powder with quinoa flour (0 to 100%), hydrogenated vegetable oil (4.5 to 8.5%) and Panisol gum (0.25 to 0.65%) to obtain the optimal formulas of Vanilla ice cream using the response surface methodology.
Materials and Methods: After adjusting the ratio of the ingredients in the various ice cream formulations, the amount of raw material of each formula was weighed. The milk was then heated to about 45 ° C, and then the remaining ingredients were slowly added and thoroughly mixed. The mixture was then pasteurized at 85 °C for 15 minutes. After the pasteurization operation, the mixture was immediately kept in a water-ice bath and cold down for 4 hours in a 4 °C refrigerator. After the ripening step, the mixture went through the freezing phase in a homemade ice cream maker. The ice cream samples were packed in plastic containers and stored at -18 °C for the period of hardening. To optimize the process conditions, the independent variables A (quinoa flour replacement from 0 to 100%), B (hydrogenated vegetable oil from 4.5 to 8.5%) and C (Panisol gum from 0.25 to 0.65%) were selected at five levels. To obtain optimal points, 34 experiments were recommended by design expert software. The volumetric overrun (%) and the melting rate (g/min.) were measured according to Hashemi et al., (2015) method. Ice cream textural properties were tested after 3 days storage at -18 °C using a Brookfield texture analyzer. It was equipped with a cylindrical probe with a diameter of 6 mm and a height of 15 mm. The probe was applied to the test samples twice at a speed of 1 mm / s and up to 50% of the probe height and the results were recorded by device software. Ice cream textural data used in this study included hardness (g) and adhesiveness (g. sec) (Hashemi et al., 2015).
Results and Discussions: Reducing overrun of ice cream samples by increasing the replacement levels of quinoa flour can be attributed to an increase in the viscosity. As viscosity increases, due to the reduced mixing ability of the ice cream mixture, the ability of air to enter the mixture of ice cream containing quinoa flour has been reduced during freezing (Gelroth et al., 2001). The reason for the decrease in the melting rate of ice cream with increasing percentage of quinoa flour replacement can be attributed to the existence of polysaccharide compounds with high water holding capacity, which led to increase the product water intake intensity and viscosity and subsequently decreasethe overrun. One of the factors affecting the melting properties is the increase in volume. In addition, the role of quinoa flour in enhancing the melting resistance of ice cream can be attributed to the type of protein content, the emulsifier potential and the surface active properties of its proteins and lipids. The presence of high amounts of protein in quinoa flour has a significant effect on the stability of air molecules. Since quinoa flour contains high amounts of protein, this fraction of flour quinoa protein, increases the hardness of ice cream through creating hydrogen bonds between the amide-hydroxyl and hydroxyl-carbonyl groups with other polar groups of other ice cream components such as panisol gum. In addition, hydrogen bonds are likely to be formed by electrostatic interactions between the quinoa protein groups of the polar with the polar part of the gum panisol, which may also be the reason for the increased hardness of the ice cream in the presence of the quinoa flour. With polar groups, quinoa flour traps the water in its structure and ultimately increases the consistency and adhesiveness of the ice cream. It is also possible that the protein portion of quinoa flour binds to the water molecules present in the sample through hydrogen bonding and ion-dipole and dipole-dipole interactions, thereby reducing water activity, increasing sample adhesiveness (Fatemi, 2008).
The optimal formulas were predicted for replacement of skim milk powder with quinoa flour at 25 and 53%, hydrogenated vegetable oil 8.5 and 8.2% and panisol gum 0.39 and 0.48%, respectively.
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