Journal of health research in community

Introduction
The process of repeatedly heating oil and its use over long periods accelerates oxidation and hydrolytic acidification. This process produces harmful substances, such as hydroperoxides, aldehydes, and polymerized triglycerides. The use of such oils has been associated with an increase in cardiovascular diseases, metabolic disorders, and cancer. Total polar materials (TPM), acid value (AV), and peroxide value (PV) are commonly used to monitor oil quality. In food service operations, variables, such as frying oil usage frequency and frying oil temperatures play significant roles in determining the level of oil deterioration. Fried meals have become popular in northern Iran, but there is limited information regarding the physicochemical properties of frying oils in food preparation centers in urban areas of northern Iran. The purpose of this research was to evaluate the quality of repeatedly used frying oils in food service operations in Gorgan city in Iran.

Methods 
This descriptive cross-sectional study was conducted in Gorgan, Iran in 2022. The study population included licensed food establishments such as restaurants, central kitchens, fast‑food outlets, and confectioneries. Stratified random sampling was applied according to the proportional size of each group. Calculations using G*Power software showed that, with an effect size of 0.5, a power of 80%, and α=0.05, the minimum required sample size was 37; therefore, 43 frying oil samples were collected to account for potential losses during the study. 
Data collection was done using a 12-item questionnaire on the operations of each food establishment regarding the type and brand of oil used, daily oil consumption, frying temperature, oil usage period, maximum oil usage period, and disposal methods for used oil. Oil quality parameters were measured three times using standard methods. Clear physical parameters included TPMs measured using the AOCS Cd 20-91 and IUPAC 2.507 methods; some of these were also verified using the Testo 270 device. AV was measured using the AOCS Cd 3a-63 method via titration with a 0.2 N KOH solution. PV was also measured via iodometric titration according to the ISO 3960 and AOCS Cd 8-53 methods (1-3). The oil frying temperatures were measured using a calibrated thermometer with a range of 40-200°C. 
The study used SPSS software, version 26 for data analysis, as the study population did not show a normal distribution according to the Shapiro–Wilk test results. Non-parametric tests were used; the Kruskal–Wallis test was applied to determine differences, and Spearman’s rho was used to determine correlations between the study parameters and oil quality indices. The study used P<0.05 as the level of significance.

Results 
On average, the total polar material (TPM) for all the samples was calculated to be 28.8% with a standard deviation of 4.8%. This is significantly higher than the international safety standard of 25%. Among all categories, confectioneries recorded the highest average total polar material (30.43±5.61%), followed by restaurants (29.94±2.38%). More than half of the restaurant and confectionery samples, and about 40% of the other centers, exceeded the recommended limit. The average AV for all the samples was calculated to be 2.87 mg/KOH/g with a standard deviation of ±1.18. Central kitchens recorded the highest average AV (3.24 mg/KOH/g±1.19). This indicates that hydrolytic degradation is advanced. High acid values reflect higher levels of free fatty acids, which may indicate reduced oil freshness and potential irritation to the gastrointestinal system. 
The average PV for all samples was calculated to be 7.8 meq/kg with a standard deviation of ±3.6, which is lower than the standard limit set by Iran (10 meq/kg). However, several samples were close to or exceeded this limit. High PVs were recorded for confectionery products, which may reflect higher frying temperatures and longer oil reuse times. The average oil usage duration for all units was calculated to be 12 hours/day, while the maximum oil reuse times for fast-food establishments, confectioneries, restaurants, and central kitchens were recorded as 96, 72, and 24 hours, respectively. The Spearman analysis revealed positive correlations between frying temperature, oil usage duration, TPM, and AVs at a significance level of P<0.05, indicating that units with longer oil usage durations recorded higher degradation values. There were no statistically significant differences in PV and AV among center types (P>0.05), showing that oil deterioration is an issue across all sectors. Regarding disposal methods, 74.4% of respondents sold used oil to soap manufacturing companies, 23.3% disposed of it with solid waste or septic systems, and only 2.3% disposed of it in wastewater systems. 

Conclusion 
The results indicated that frying oils are being managed rather poorly in different food preparation centers in Gorgan. Although most peroxide value results remained within acceptable limits, the higher TPM and AV results indicate that oil degradation from repeated heating and reuse persists. This is consistent with findings from other Iranian cities. When TPM exceeds 25%, it indicates an increase in oxidized triglycerides and polymers, which are associated with oxidative stress and chronic inflammation. Operational variables, particularly duration of reuse and temperature, were more influential predictors of frying oil quality than the type of food preparation establishment. The overall results highlight the need to improve monitoring and operator training, as well as the implementation of standardized procedures for changing frying oils. Developing a formal system for collecting and recycling used frying oils could further reduce environmental and health risks. 

Ethical Considerations
Compliance with ethical guidelines
The study protocol was approved by the Ethics Committee of Golestan University of Medical Sciences (Code: IR.GOUMS.REC.1401.255). 

Funding
This manuscript is derived from an approved research project and was financially supported by Golestan University of Medical Sciences (Grand No.: 112866).

Authors contributions
All authors contributed equally to study design, data collection, data analysis, manuscript drafting, and approval of the final version.

Conflicts of interest
The authors declared no conflicts of interest.

Acknowledgments
The authors gratefully acknowledge the cooperation of the Environmental Health Department of Golestan University of Medical Sciences and the participating food establishment managers.
 



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