Variety of EnergeticConsistency of Oxidized and Non-Oxidized Corn Oils with Temperature

Introduction

Vegetable oils and fats have an important role in human vital activity, representing an important energy source and an important food component. For this reason, vegetable oils are widely used in various fields of the food industry. The particularity of vegetable oils consists in their high content of unsaturated fatty acids and as a result their oxidation under the action of air oxygen, the speed of the oxidation process increasing with increasing temperature. The oxidation processes that take place at high temperatures in the food preparation process and the compounds that are formed reduce the quality of the oils, a fact that requires research into the changes that take place in the frying process. Lipid oxidation leads to a reduction in nutritional value and, as a result, negatively affects the sensory characteristics of lipid-containing products.^1–5

In fact, lipid autoxidation and limited antioxidant capacity play a key role in reducing the shelf life of vegetable oils, leading to alterations in color, texture, aroma, flavor, and the loss of vitamins.^6-11

Corn oil is derived from corn germs, which contain 20–30% oil and are a byproduct of corn degermination for sorghum or the production of starch, ethanol, and other products. The extraction process involves pressing and solvent extraction, followed by refining. Refined corn germ oil possesses excellent sensory qualities and a high content of essential fatty acids, making it valuable in dietary products due to its cholesterol-lowering effects. It also features low free acidity (maximum 0.3% oleic acid) and minimal water content.^11-18

Materials and Methods

To determine how viscosity varies with temperature and shear rate, the Rheotest2 device was employed. Corn oil was subjected to oxidation at 110°C and 120°. Dynamic viscosity corn measured at both temperatures and oxidation periods, respectively test temperatures, dynamic viscosity decreases with increasing shear rate for corn oil.

Results and Discussion 

Graphs 1 and 2 show the change in viscosity as a function of temperature for corn oils oxidized at both oxidation times, and for each shear rate, the dynamic viscosity decreases as the test temperature increases.

Figure 1: Graph for a shear rate of 3.3 s⁻¹ of oxidized corn oil at 110°C (a) and 120°C (b). Click here to View Figure

Figure 2: Graph for a shear rate of 80 s⁻¹ of oxidized corn oil at 110°C (a) and 120°C (b).  Click here to View Figure

Oxidation of corn oil at high temperature does not lead to significant increases in dynamic viscosity compared to unoxidized oil. Increasing the oxidation temperature from 110°C to 120°C leads to an increase in the energy consistency of the oxidized oil for 10 hours. Azian equation (1) provides a good fit to the experimental data and is temperature dependent in the case of oils.

Where T is the absolute temperature, and A, B and C are material constants.^6,7

Table 1 presents the material constants A, B and C as well as the correlation coefficients of the Azian equation.

Table 1: The values ​​of the parameters of the Azian equation

Graphs 3, 4 and 5 present viscosity maps showing the combined effect of temperature for corn oil.

Figure 3: Maps showing the combined effect of temperature for corn oil unoxidized. Click here to View Figure

Figure 4: Maps showing effect corn oil oxidized at 110°C. Click here to View Figure

Figure 5: Maps showing oil oxidized at 120°C. Click here to View Figure

Graphs 6 and 7 show the experimental values ​​for corn oils oxidized.

Figure 6: Graph experimental results for corn oil oxidized at 110°C for 5 hours (a) and 10 hours (b). Click here to View Figure

Figure 7: Graph experimental results for corn oil oxidized at 120°C for 5 hours (a) and 10 hours (b). Click here to View Figure

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Conclusion

Oxidizing corn oil at 110°C and 120°C for 5 and 10 hours leads to an increase in dynamic viscosity compared to unoxidized oil—an effect observed across all test temperatures. A significant increase in dynamic viscosity is observed as the oxidation time extends from 5 to 10 hours. The most notable rise occurs at an oxidation temperature of 120°C for oil oxidized over 10 hours, with the test temperature set at 30°C. When the test temperature is raised from 30°C to 90°C, the increase in dynamic viscosity becomes less pronounced. 

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