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ORIGINAL ARTICLE
Int J Env Health Eng 2019,  8:6

Investigation of cooking oil quality at fast food restaurants in Mashhad City


1 Department of Environmental Health Engineering, Social Determinants of Health Research Centre, School of Health, Gonabad University of Medical Sciences, Gonabad, Iran
2 Department of Environmental Health Engineering, School of Health, Torbat Jam Faculty of Medical Sciences, Torbat Jam, Iran
3 Department of Environmental Health Engineering, Student Research Committee, School of Health, Mashhad University of Medical Sciences, Mashhad, Iran
4 Department of Social Medicine, Social Determinants of Health Research Centre, School of Health, Mashhad University of Medical Sciences, Mashhad, Iran
5 Department of Environmental Health Engineering, Faculty of Health, School of Health, Mashhad University of Medical Sciences, Mashhad, Iran
6 Department of Environmental Health Engineering, Student Research Committee, School of Health, Gonabad University of Medical Sciences, Gonabad, Iran

Date of Submission06-May-2019
Date of Acceptance16-Jul-2019
Date of Web Publication29-Nov-2019

Correspondence Address:
Mahnaz Kharghani
Department of Environmental Health Engineering, Student Research Committee, School of Health, Gonabad University of Medical Sciences, Gonabad
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijehe.ijehe_2_19

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  Abstract 


Aims: Deep frying of foods at high temperatures results in an increase in the unique sensorial properties of fried food including fried flavor, golden brown color, and crispy texture, which ultimately leads to changes in the physical and chemical properties of the oil. This study was conducted to evaluate the quality of oils used in 60 centers of fast food distribution in Mashhad city. Materials and Methods: A validated questionnaire based on the instruction from the Ministry of Health and Medical Sciences was used to collect the data and to investigate the health status of the places and foods. Total polar material (TPM), temperature, and acidity of the oil were measured using oil test portable device (DOM-24 model) while the peroxide value (PV) was measured by iodometry method. The data were analyzed by SPSS software V.16 via statistical tests including t-test, ANOVA, and Chi-squared tests.Results: The mean values of TPM, acidity and PV in the studied oils were 31.8 ± 7.2 %, 3.7 ± 0.8, 4.7 ± 6.7 meq/kg, respectively. There was a significant relationship between TPM value with acidity, temperature and duration of oil use based on Pearson correlation test (P > 0.005). Furthermore, there was a significant relationship between the PV and area, the type of oil, and sanitation of instruments. Conclusion: The levels of hydrogen peroxide, polarity, and acidity of oils in fast food shops were higher than the guideline values. We recommend that health inspectors systematically monitor the oils fried in these centers.

Keywords: Fast foods, food handling, oxidants, toxicity


How to cite this article:
Sajjadi SA, Moteallemi A, Bargard ZR, Aghaee Naeein MA, Kariminezhad F, Kharghani M. Investigation of cooking oil quality at fast food restaurants in Mashhad City. Int J Env Health Eng 2019;8:6

How to cite this URL:
Sajjadi SA, Moteallemi A, Bargard ZR, Aghaee Naeein MA, Kariminezhad F, Kharghani M. Investigation of cooking oil quality at fast food restaurants in Mashhad City. Int J Env Health Eng [serial online] 2019 [cited 2019 Dec 10];8:6. Available from: http://www.ijehe.org/text.asp?2019/8/1/6/272020




  Introduction Top


Nutrition is one of the most important factors that affect the people's health. The pattern of food consumption has also an important role in causing or preventing diseases.[1] Oils are the main components of a diet whose proper use can be helpful in preventing certain diseases. Edible oil is a source of energy and essential fatty acids (FAs) and a carrier of fat-soluble vitamins.[2],[3] Fried foods are very popular for consumers because of the speed of their preparation and the fascination in color, flavor, texture, and taste.[4] One of the most popular and sophisticated food preparation methods is the deep-frying process, which is usually practiced by fast food centers.[5],[6] The quality of fried food depends on the quality of the oil or fats.[7] During the frying process, oil or fat is often used several times. In this way, humidity and air are mixed with hot oil and cause chemical reactions in the oil used for frying. As a result, these fats and oils are affected by the autoxidation, thermo-oxidation, pyrolysis, and thermal polymerization as well as oxidative decomposition, which alter and degrade the composition of the oil. All these lead to production of by-products such as dimeric and polymeric materials which can be harmful to health.[8]

The type, formation, and amount of these harmful products are different based on the parameters of the frying process.[9],[10],[11] The most important parameters in the frying process include the nature of frying oil, temperature, frying time, the frying pan, and the moisture of food. Among these parameters, the nature of frying oil acts as a heat transfer medium and affects the quality of fried foods.[12],[13] This quality is also influenced by the properties of the oil.[9],[10]

In the long-term use of oils, their oxidation occurs with more production of hydroxides and volatile compounds such as aldehydes, ketones, carboxylic acids, and other undesirable chemicals.[12],[14] The consumption of fried foods with repeatedly used oils is unhealthy and increases the chance of cardiovascular disease.[14] Oil oxidative degradation results in undesirable flavor and partial or whole destruction of vitamins and other nutrients at different stages of oxidation. Oxidized fat reacts with proteins and carbohydrates, causing important chemical changes in food.[15] Hydrogen peroxide is a polar covalent compound. Studies have shown that peroxides can cause various diseases, including atherosclerosis, cancer, premature aging, allergic inflammation, cardiac and cerebral ischemia, and various liver disorders.[8],[10]

In some countries of the world, to ensure the quality of oil, some provisions have been made for degraded compounds of the oil that are unsuitable for human consumption.[16] Peroxide value (PV) is one of the most common parameters to determine the oil quality in production, storage, and marketing processes specifically determining the oxidation degree of oil.[17] This index is one of the quality control methods of edible oils, which measures the concentration of unstable hydroxides that easily decompose to secondary oxidation products.[18] The standard of polar compounds and free FA (FFA) in Iran is 25% and 1%, respectively.[19] Accordingly, different studies have been conducted to determine the quality of fried oil in Iran and other countries of the world. For example, the results of a study conducted in Gorgan, Iran showed that the oil PVs were higher than the standard levels in 44% of confectioneries, 60% of restaurants and kitchens, and 82% of fast food stores. In a study conducted in Toronto on the health of the oils used in restaurants, it was observed that the PV was higher than the allowable level in all used oils.[16] In a study conducted in Toronto on the health of the oils used in restaurants, it was observed that the PV was higher than the allowable level in all used oils.[14]

Mashhad is located in Razavi Khorasan province, Iran. Because of the existence of the shrine of Imam Reza, Mashhad annually welcomes over 32 million pilgrims. Thus, due to the importance of edible oils as well as its effects and risks to the human health, this study was performed to determine the quality of edible cooking oil at fast foods of Mashhad city in 2017.


  Materials and Methods Top


This descriptive cross-sectional study was conducted on 60 fast food stands in Mashhad, Iran in 2017. The sample size was calculated using the following formula:



where n is sample size, Z is confidence interval and p is standard deviation

In this study, the quality of oil consumed was studied based on PV, acidity, and the total amount of polar compounds (TPCs). A validated checklist based on an instruction from the Ministry of Health and Medical Sciences was used for data collection.[20] The most important questions of the checklist were as follows: demographic characteristics of individuals (sex, age, education, work experience, card and health certificate), type of food, hygiene status of fast food center and oil specifications including type of oil, duration of oil used, oil temperature.

The number and frequency preparation of studied fast food centers are presented in [Table 1].
Table 1: The frequency of preparation and distribution of fast food centers

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Oil sampling was carried out according to Iranian national standard (No. 493).[19] A total of 60 oil samples were collected from the fast food stores at peak times (18–23 pm) given the greater activity of these centers at these times, from Wednesday to Friday. The samples were collected by clean and unbreakable glass containers. Sampling containers did not chemically affect the oils. The samples were then transferred to the approved laboratory of the province's health center as quickly as possible and under the temperatures of 5°C–15°C. The PV of samples was measured by iodometry method and based on standard of Iran No. 4179. Finally, the results were reported in meq of peroxide/1000 g.[21]

To measure total polar material (TPM), temperature, and FFA, the DOM-24 portable test device, manufactured by Japan ATAGO Corporation, was used based on the device guidelines. Data were analyzed by SPSS (version 16, IBM, IL, USA) and ANOVA, t-test, and Chi-squared tests.


  Results Top


This study was conducted on 60 fast food shops in Mashhad. The frequency of preparation and distribution of fast foods has been presented in [Table 1]. Among the studied fast food managers, 59 of them were male and 1 was female. The maximum age range of the individuals was 26–40 years. The level of education of most people studied was diploma. Further, 60% of the providers had a work experience under 5 years. Notably, 25% of the providers of fast foods did not have any health cards and 46.7% lacked health certificates; this health problem threatens the people's health in the community.

In addition, the environmental health status of 13.3% of the studied shops was unsuitable. Specifically, 16 cases (26.7%) of the studied shops had self-control certificate and 7 cases (11.7%) had health counseling. On the other hand, 37 cases (61.7%) of the studied centers did not have any health counseling, which can be the reason for the inappropriate health status of some centers. Furthermore, the preparation area of shops in 40% cases was <25 m 2 [Table 2]. In this study, 90% of the fast food distribution centers used a special frying oil, 5% used solid oil, and 5% cooked through liquid oil for frying.
Table 2: The scores of indicators in the checklist of regulation of 13 Act of Iran

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The TPM value in terms of the number and temperature of utilized oils is presented in [Figure 1] and [Figure 2]. The highest value of measured TPM was related to oils with seven times of use and within the temperature range of 180°C–160°C, while the lowest TPM was associated to oils with one time of use within the temperature range of 60°–40°C.
Figure 1: Determination of the total polar material value in terms of number of oil used

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Figure 2: Determination of the total polar material value in terms of the oil temperature used

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[Figure 3] and [Figure 4] display the amounts of FFAs in terms of the number and temperature of oils used. The maximum level of FFA was related to temperature range of 160°–180°C of used oils while the minimum value was associated to temperature range of 40°C–60°C. The maximum magnitude of measured FFA was related to oils with seven times of use, while their lowest was related to oils with one time of use.
Figure 3: Determination of the free fatty acids used in terms of the number of oil used

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Figure 4: Determination of free fatty acid in terms of the temperature of used oils

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The PVs in terms of the number and temperature of oils used are presented in [Figure 5] and [Figure 6]. [Table 2] reports the values of oil chemical parameters in fast food restaurants. According to [Table 2], the values of TPM, acidity, peroxide, and oil temperature were 31.9 ± 7.2 %, 3.7 ± 0.8, 4.7 ± 6.7 meq/kg, respectively.
Figure 5: Determination of peroxide value in terms of oil used

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Figure 6: Determination of peroxide value in terms of the oil temperature used

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  Discussion Top


Total polar material

TPM refers to the extent of oxidative thermal degradation of frying oil and is one of the objective criteria for assessing the deterioration of cooking oil.[22] During frying processes, peroxides and hydroxides are degraded to short chain acids and aldehydes, ketones, alcohol, and nonvolatile products which will cause polarization.[23],[24]

TPM involves the polymer products and nonvolatile aromatic materials (resulting from the oxidation and hydrolysis of oil) and soluble compounds generated from the fried product.[22] In Spain, Austria, Switzerland, France, and Belgium, TPM is used as a tool to determine the usage time of frying oil.[24]

According to [Table 3], the mean of TPM in this study was 31.85 ± 7.17 % in the studied centers which has been higher than the standard values. The highest value of measured TPM was related to oils with seven times of use and within the temperature range of 180°C–160°C, while the lowest TPM was associated to oils with one time of use within the temperature range of 60°C–40°C [Figure 1] and [Figure 2]. With elevation of temperature and frequency of oils used, the TPM increased. Nevertheless, the results indicated that the type of oil used did not affect the TPM value.
Table 3: The mean of oil used indicators in studied fast food centers

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Park and Kim revealed that the extent of laboratory polarization increased during the frying process and was strongly correlated with frying time.[3] The results of a study conducted by Hassanien and Sharoba showed that the polarity in 7% of the samples was higher than the standard values. In this study, the magnitudes of laboratory polarity in 17% of rapeseed oil and 2.2% of sunflower oil were higher than the acceptable limit.[25] Sebastian et al. investigated the quality of oil used in fast food restaurants in Toronto, Canada. They found considerably high PVs (ranging from 3.3 to 48.1 meq/kg compared to 23.9–31.85 meq/kg in the current study).[18] Most studies on the effect of oil frying on chemical characteristics of oils have been conducted in laboratory settings. They found that the magnitudes of PV and TPCs increased following heating oil at high temperatures.[26] Nevertheless, it seems that under real conditions, i.e., in fast food restaurants, the extent of changes in chemical parameters is far more considerable (sometimes 10–20 times) than in laboratory conditions. Latha and Nasirullah reported that by 8 h heating of oil at 180°C, the PVs and TPM increased to 2.9 meq/kg and 1.8%, respectively.[26] On the other hand, in the current study, the corresponding values increased on average to 31.85 meq/kg and 4.67% ± 4.68%.

Fatty acid

According to [Table 3], the mean of FFA in oils used was 3.73 ± 1.82 [Table 3]. The maximum level of FFA was related to temperature range of 160°C–180°C of used oils while the minimum value was associated to temperature range of 40°C–60°C. The maximum magnitude of measured FFA was related to oils with 7 times of use, while their lowest was related to oils with one time of use [Figure 3] and [Figure 4].

Pearson correlation test revealed a significant relationship between TPM value and acidity, temperature, and duration of oil use (P < 0.05). In the oils with a longer duration of use and higher temperatures, the polarity and acidity increased and the oil was deteriorated gradually. Vinci et al. showed that only 44% of oils used for frying chicken nugget was in standard range, and in 36% of the cases, the oil was used up to complete corruption.[27] This is similar to the current study. The results of the study conducted by Mishra and Sharma suggested that the level of unsaturated FA decreased gradually during repeated deep fat frying cycles in both oils.[28]

Peroxide number

PV is the most common parameter used to evaluate the oxidative status of oils. According to [Table 3], the amount of peroxide in the oil samples was 0.38–31.35 meq/kg. The highest measured PV was related to oils with 6 times of usage within the temperature range of 60°C–80°C. In contrast, the lowest magnitude was obtained in oils with five times of use within the temperature range of 160°C–180°C [Figure 5] and [Figure 6].

These PVs indicate that the oils used in these centers are highly oxidized. Note that the initial oxidation products quickly decompose into secondary oxidation products, which in turn reveal their accumulation in total oil less than the actual value. The standard PV in Iran is 2 mg/kg for solid oil and 5 mg/kg for liquid oil; the amount of peroxide in studied samples exceeded the standard value and is hazardous to human health.

There was a significant relationship between the level of peroxide and the type of oil consumed as well as the amount of peroxide and sanitation of equipment (P < 0.05). This indicates that regular and daily washing of the tool of work and place of production has a significant effect on reducing the PV.

In the study conducted by Sebastian et al. in Canada, the range of PV was within 3.3–48.1 meq/kg.[18] In a study conducted in Shahrekord, the amount of peroxide in the samples was higher than the standard limit, which is consistent with the present study.[25]

High levels of peroxide can be due to repeated use of oils, inappropriate sanitary conditions of the places and equipment, and the lack of personal hygiene. Meanwhile, oven is not cleaned daily, and the oil is burnt whereby the amount of peroxide grows constantly.[3]

The results of several studies have suggested that the PV decreases during the frying time.[13],[15],[23] The storage of oil leads to an increase in PV. On the other hand, the use of oil for frying does not lead to a significant increase in PV since the peroxides spontaneously decompose at temperatures over 150°C.[29] Chen et al. revealed that the highest PV value was found at temperature of 150°C, beyond which this value decreased significantly at 200°C and then slightly increased at 250°C.[30]

The results of Birjandi et al. suggested that the lowest and highest PV were 1.1 and 2.9 meq/kg, respectively. The minimum and maximum acidity of the samples were 0.7 and 2.9 wt%, respectively. They results revealed that the PVs in Persian doughnuts in Lorestan province were higher than the standard limit. Furthermore, by increasing the heating time and the frequency of oil use, the chemical reactions and the PV increased.[29]

The smoke produced during the cooking, oil opacity, the lack of changes in the oil, the unpleasant smell, and finally, the high PV of the oils consumed suggest the existence of harmful and toxic compounds in the foods provided in fast foods restaurants.

Ghobadi et al. surveyed acid and PVs and TPC of frying oils in fast food restaurants of Shiraz. They found that the acid and PVs of 27 samples (64.3%) were higher than the permissible value. This number for TPC was 19 (45.2%).[31]

The study conducted by Sebastian et al. revealed that the PVs were as high as 10 meq/kg, and FFA level was higher than 1%, and suggested that 30%–35% of in-use frying oils and 45%–55% of discarded oils were higher than the acceptable values.[18]


  Conclusion Top


In the current study, it was observed that the mean of TPM, FFA, and hydrogen PVs in the oils used in the studied fast foods were 31.85 ± 7.17, 3.73 ± 0.82, and 4.67 ± 6.68, respectively. The results showed that by increasing the oil temperature and the frequency of the oils use, the extent of polarity and acidity increased, which can lead to deterioration of the oil consumed. Furthermore, by raising the oil temperature, the initial oxidation products decompose to secondary oxidation products quickly; as a result, the measured PV obtained was less than its actual value. Thus, the PV is not a proper indicator for assessing the quality of the oil. The high temperature of the oil for frying produces various toxic materials which affect the quality of the food and seriously threatens the consumers' health.

Acknowledgment

The authors are grateful to the Vice-chancellor for the Research and Technology, Gonabad University of Medical Sciences for the financial support of this project (No. 97/4/P).

Financial support and sponsorship

Gonabad University of Medical Sciences, Gonabad, Iran.

Conflicts of interest

There are no conflicts of interest



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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