Determination and prediction of discharge point of industrial and guilt frying oil during deep frying

Introduction: The frequent and long-term use of a significant amount of frying oil at temperatures between 150 °C and 190 °C to heat and immerse food is called deep frying. This method of food preparation due to the creation of attractive sensory and organoleptic features, including texture crispness, good taste, increasing the speed of cooking, and producing food products with a unique aroma,taste and brown color has been noticed by all the people of the society, especially the youth (Asokapandian et al., 2020). In the process of deep frying, as a result of the interaction between oil and other factors such as moisture, oxygen and heat, the main and complex chemical reactions of hydrolysis, oxidation, denaturization, isomerization and polymerization occur, by transferring moisture from the food to oil and absorption of oil into food leads to the production of harmful compounds and the reduction of oil quality, as well as chemical changes and mechanical deformations such as wrinkling, expansion and crust formation in fried food products (Dash et al., 2022). The extent of these changes depends on various factors, such as the characteristics of food and oil, the type of fryer, the type of heating process, the increase in factors such as the rate of integration of air and oil, the number of times of frying, and the duration of immersion of the food. Considering the very unfavorable effects of these reactions on oil quality, in order to reduce corruption and to identify and determine the point of oil disposal during the deep-frying process, various important indicators have been determined. The most important of these indicators are polar compounds, anisidine value, peroxide, volatile and non-volatile compounds, peroxide number, free fatty acids, acid value, iodine number, and smoke point. This study aimed to investigate the possibility of determining and predicting the tipping point of frying oil during deep frying (Xu et al., 2019).
Material and methods: For this purpose, on four consecutive days for 6 h with 45 minintervals, 100 g of semi-prepared potatoes from the Paris brand for 8 to 10 min in a fryer containing 4 L of Aftab brand oil. It was fried at a temperature of 180 oC, at the end of 6 hours of work, the fryer was turned off and some of the oil inside the fryer was removed in a container, after cooling the oil inside the container, 3 Falcon tubes of 50 ml (total 150) of the oil sample was separated to evaluate and perform various tests, and after labeling, it was placed in the freezer at -10 oC. To evaluate the changes in the oil used on the 4 day samples and the control sample (total of 5 samples), tests of anisidine, peroxide, acidity, polar compounds, and absorption in the region of 200 to 900 nm at a wavelength of 380 nm were performed. Suitable kinetic modeling was performed using MATLAB software, and these changes were interpreted using SPSS software with a confidence level of 95%. In previous studies, the changes in the oil factors of trade and industry were evaluated and investigated, but the amount of absorption in a certain spectrum and the use of this factor to determine and predict the tipping point of oil have received less attention (Senanayake 2018).
Results and discussion: In this study, it was found that with the increase in the time of frying potatoes, the amount of acidity, polar compounds, anisidine value and absorption in the fried oil increased, and statistically, these changes were significantly different from they also have (p≤0.05). Thus, the lowest level of acidity was related to the control treatment, and the highest level of acidity was related to the fourth-day sample. The peroxide changes first increased and then decreased, and the changes in this treatment were different from those of the other treatments. The acidity and anisidine values passed the point of corruption of these factors, but polar compounds and peroxide did not reach this point. The anisidine values were significantly different between the treatment and control samples (p≤0.05). As the number of days passed, the amount of anisidine in the fried oil increased, which was statistically significant (p≥0.05). Thus, the lowest number of anisidines was related to the control treatment, and the highest number of anisidines was related to the fourth-day sample. There was a significant difference in polar compounds between the treatment and control sample (p≤0.05). As the number of days elapsed, the number of polar compounds in fried oil increased, with a statistically significant difference (p≤0.05).Thus, the lowest amount of polar compounds was related to the control treatment, and the highest amount was related to the sample on the fourth day. The absorption at in 200-900 nm was significantly different between the treatment and control samples (p≤0.05). With the passage of time, the amount of absorption in 200-900 nm range in fried oil increased, which was statistically significantly different (p≤0.05). Therefore, the lowest absorbance at 200-900 nm was related to the control treatment and the highest absorbance at 200-900 nm was related to the fourth-day sample. Researchers believe that the measurement of polar compounds is the most important test in oil decomposition. The amount of polar compounds during a certain period of margarine heating is a function of the amount of moisture and oil phase used (including the resistance of the oil to oxidation, the amount of mono- and diglycerides, free fatty acids and oxidized triglycerides).
Conclusion: Measuring and checking the changes in oil factors, as well as using the intensity of absorption of polar compounds at different intervals in determining the spoilage and waste of industrial frying oils is a very suitable and practical method. The results of this research show that theabsorption index of polar compounds can be used to determine the pour point of oils used in frying.