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Khalili N, Akrami Mohajeri F, Ramroudi F, Mojaver F, Hakimi F, Sardari M, et al . Quality Assessments of the Fried Oils in Fast Food Restaurants of Yazd, Iran. JNFS 2020; 5 (3) :201-208
URL: http://jnfs.ssu.ac.ir/article-1-242-en.html
URL: http://jnfs.ssu.ac.ir/article-1-242-en.html
Narjes Khalili 
, Fateme Akrami Mohajeri , Fereshteh Ramroudi , Fatemeh Mojaver , Fatemeh Hakimi , Maryam Sardari , Mahboubeh Khebri , Elham Khalili Sadrabad *
, Fateme Akrami Mohajeri , Fereshteh Ramroudi , Fatemeh Mojaver , Fatemeh Hakimi , Maryam Sardari , Mahboubeh Khebri , Elham Khalili Sadrabad *
Zoonotic Diseases Research Center, School of Public Health, Department of Food Hygiene and Safety, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
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Quality Assessments of the Fried Oils in Fast Food Restaurants of Yazd, Iran
Narjes Khalili; MD, PhD1, Fateme Akrami Mohajeri; PhD2, Fereshteh Ramroudi; MSc2, Fatemeh Mojaver; BSc3, Fatemeh Hakimi; BSc3, Maryam Sardari; BSc3, Mahboubeh Khebri; BSc3 & Elham Khalili Sadrabad; VMD, PhD*2
Narjes Khalili; MD, PhD1, Fateme Akrami Mohajeri; PhD2, Fereshteh Ramroudi; MSc2, Fatemeh Mojaver; BSc3, Fatemeh Hakimi; BSc3, Maryam Sardari; BSc3, Mahboubeh Khebri; BSc3 & Elham Khalili Sadrabad; VMD, PhD*2
1 Preventive Medicine and Public Health Research Center, Department of Community Medicine, School of Medicine, Iran University of Medical Sciences. Tehran, Iran.
2 Zoonotic Diseases Research Center, School of Public Health, Department of Food Hygiene and Safety, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
3 Environmental Science and Technology Research Center, Department of Environmental Health Engineering, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
2 Zoonotic Diseases Research Center, School of Public Health, Department of Food Hygiene and Safety, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
3 Environmental Science and Technology Research Center, Department of Environmental Health Engineering, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
| ARTICLE INFO | ABSTRACT | |
| ORIGINAL ARTICLE | Background: Oils and fats are among the important constituents of foods. Lipid oxidation can cause changes in taste, flavor, smell, color, texture, and nutritional value of the foods. Deep-fat frying (temperatures of 150 to 200 °C) leads to a series of chemical and physical reactions, so that the oil is oxidized, polymerized, and hydrolyzed. Methods: In a current descriptive cross-sectional study, 100 oil samples were obtained from fast food shops in Yazd city during the spring and summer of 2018. A checklist was prepared including the oil type (oil or fat), odor, color, smoke, and duration of use. The peroxide value (PV), p-anisidine value (p-AV), free fatty acid (FFA) levels, and total polar compound (TPC) of the samples were examined. Results: We found that 93% of the oil samples were in form of liquid. In term of color, 45% of the samples had a dark color and about 57% had an undesirable odor during cooking. In 23% of the fast food shops in Yazd, oil is used more than two days. The measurement of peroxide value showed that 73 samples had peroxide values higher than the allowable limits. The allowable average peroxide value was estimated as 2.33 meq/kg. Results showed that 56 samples had allowable FFA level (less than one), while the others were classified as oxidized oils. The p-AV in 55% of the oil samples were higher than 4. According to the results, 46% of the frying oil samples had TPC of higher than 25%, which showed that they should be discarded. Conclusion: The results showed that majority of the fast food shops in Yazd used highly oxidized oils to prepare their food. The absorption of such oils by food can endanger the public health. Therefore, continuous monitoring of fast foods and restaurants as well as training the staff seem necessary. Keywords: Oil; Peroxide value; Free fatty acid; P-anisidine value; Total polar compound; Yazd |
|
| Article history: Received: 2 Feb 2019 Revised: 21 Jun 2020 Accepted: 18 May 2020 |
||
| *Corresponding author: Khalili.elham@gmail.com Zoonotic Diseases Research Center, School of Public Health, Department of Food Hygiene and Safety, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Postal code: 8915173160 Tel: +98- 9131946425 |
Introduction
Due to the recent changes in eating habits and lifestyle of people, consumption of ready-to-eat foods have increased (Nafez et al., 2018). Food is one of the major sources of chemical and biological contamination. In this regard, oils and fats are among the three major groups of food ingredients along with proteins and carbohydrates (Takeoka et al., 1997). Fats and oils can be oxidized during the processing and storage (Farrokhzadeh et al., 2017). This reaction can lead to changes in the taste, smell, color, texture and, appearance of the oil and reduce its nutritional value (Gotoh and Wada, 2006). Over the last six decades, deep-fat frying has been one of the usual ways of food preparation. Deep-fat frying is a process of cooking, in which the food is immersed in the edible oil at a temperature of 150 to 200 °C. In this method, the thickness of the oil is from 20 to 200 mm and the oil is used repeatedly (Karakaya and Şimşek, 2011). In the frying process, a series
of chemical and physical reactions occur and the
oil undergoes thermal oxidation, polymerization, and hydrolysis. During these reactions, formation
of hydroperoxides and high molecular weight products, such as polar compounds and triacylglycerides increase (Karakaya and Şimşek, 2011). Formation of these polar compounds is related to the primary and secondary oxidation that occurs during frying. Some of these compounds are harmful to human health and contribute to tissue damage, inflammatory diseases, arthrosclerosis, and aging process (Karakaya and Şimşek, 2011). Hydrolytic decomposition occurs after breakage of the triglyceride molecules and leads to the formation of free fatty acids (FFA). The FFA can affect the odor, taste, and other properties of the oil (O'brien, 2008).
One way to identify the oil quality and early stages of oxidation is evaluating the peroxide and FFA levels. The peroxide value measures the total amount of peroxide in oil, as meq of oxygen per kilogram of oil. The FFA level is defined as the number of mg of potassium hydroxide needed to neutralize FFAs in one gram of oil sample. The FFA level is an index for measuring the amount of FFA. Free fatty acids alone are not poisonous but can affect the quality of food (O'brien, 2008). In general, both values are necessary to control the food safety and quality of oils (Gotoh and Wada, 2006). Hydroperoxides, primary products of lipid oxidation, are gradually converted to secondary ones, such as aldehydes, alcohols, carboxylic acids, epoxides, and hydrocarbons (Ruíz and Lendl, 2001). The peroxide value shows the initial stages of oxidation. The peroxide value is measured by weighing the samples, dissolving in chloroform, acidifying by acetic acid, adding potassium
iodide and sample incubation, and then titrating with sodium thiosulfate (Ruíz and Lendl, 2001). The amounts of FFAs produced during the
lipid oxidation can be evaluated by titration
using potassium hydroxide or sodium with phenolphthalein reagent, which is referred to as FFA level (Decker et al., 2010). Frying oils with a FFA level of 1 to 4% are unacceptable. The anisidine value is used for measuring the high molecular weight of saturated and unsaturated compounds in triacylglycerols (Moigradean et al., 2012). Considering the hydrolytic reactions during frying, p-anisidine value (p-AV) could be used as an indicator of oil quality assessment (Farhoosh et al., 2009). Determination of the oxidative breakdown products in frying oils can be measured by total polar compound (TPC) analysis (Sebastian et al., 2014). Productions of the polar compounds have negative effects on frying oil quality, flavor, and nutritional value of fried food (Li et al., 2016). It should be noted that the chemical composition of the frying oil and its physical and chemical properties are important in stability of the oil against oxidation. Therefore, selection of a suitable type of oil for frying is an important problem (Karakaya and Şimşek, 2011). Thermo oxidation reaction due to high temperatures causes extensive chemical and physical changes in oil (Nassehinia and Ahrari, 2016).
Owing to the importance of oil safety and its absorbance by fried foods, the current study attempted to investigate the quality of oils used in fast food shops of Yazd city in 2018.
Materials and Methods
Sampling: In the current descriptive cross-sectional study, 100 oil samples were obtained from fast food shops in Yazd city during spring and summer of 2018. A checklist containing the oil type (oil or fat), odor, color, smoke, and duration of use was prepared and completed at the time of sampling. Samples were collected according to the recommendations provided by Institute of Standards and Industrial Research of Iran (No. 493) (Institute of Standards and Industrial Research of Iran, 2004, Takeoka et al., 1997). Sampling was performed at peak hours (9 to 12 p.m). The collected samples were kept at 5-15 °C until the test was performed.
Peroxide value (PV): Peroxide value was determined based on the standard method (No. 4179) presented by Institute of Standards and Industrial Research of Iran. According to this standard, the permissible PV in fat and oil is 5 and 2 meq/kg, respectively (Institute of Standards and Industrial Research of Iran, 2004). For this purpose, 5 g of oil samples was weighed and 30 ml of acetic acid-chloroform solution (3 to 2) was added. Later, 0.5 ml of the saturated potassium iodide solution was added and placed one minute in the dark. Next, 30 ml of distilled water was added and titrated by sodium thiosulfate (0.1 N) in the presence of starch reagent. The PV (meq/kg) was evaluated according to the equation:
PV = (V-Vb) × N × 1000/W
Where, V and Vb are the volume of used sodium thiosulfate by sample and blank (ml), N is concentration of sodium thiosulfate, and W is the oil weight (g) (Rahimzadeh Barzoki et al., 2013).
Free fatty acid: In order to determine the FFA, 30 ml of the neutral ethanol was added to 5 g of oil and titrated with potassium hydroxide in the presence of phenolphthalein reagent until the pink color appeared and stable. The FFA was evaluated as below:
FFA = 5.611 × N × V/W
Which, N is potassium hydroxide concentration, V is potassium hydroxide volume used for titration (ml), and W is the oil weight (g) (Hassanzadazar et al., 2018, Sebastian et al., 2014).
P-anisidine value: p-anisidine value was evaluated using AOCS Official Method Cd 18-90 method. The oil samples (W: 0.5 g) were diluted with isooctane (25 ml) and absorbance was measured at 350 nm by UV-Visible spectrophotometer (Ab). Later, 5 ml of diluted sample was mixed with 1 ml Anisidine solution (0.25% p-anisidine in acetic acid) and the absorbance was read at 350 nm against isooctane and anisidine solution as blank (As) (American Oil Chemists' Society, 1998, Zhang et al., 2010). The anisidine value was calculated according to the following equation:
Anisidine value = 25 × (1.2As-Ab)/W
Total polar compound (TPC): The TPCs of oil samples were measured by TestoTM 270 cooking oil tester, which showed the changes in dielectric constant of oil related to TPC concentration of oil samples (Song et al., 2017).
Results
As shown in Table 1, about 93% of the samples were oils (in form of liquid). Approximately 45% of the samples had a dark color and about 57% of the samples had an undesirable odor during cooking. As a result, in 23% of the fast food shops, oil was used more than two days.
Table 2 shows the average amount of peroxide and FFA levels in the oils used in fast food shops in Yazd. Among all studied oil samples, peroxide values were higher than the permissible limit in 73 samples. The average permissible peroxide value was estimated as 2.33 meq/kg. In this study, the lowest and highest peroxide values in oil samples were calculated to be 0.56 and 286.49 meq/kg, respectively.
According to the results, most oil samples were oxidized and the production of hydroproxides small volatile molecules, such as aldehydes, ketones, carboxylic acid, and short-chain alkanes not only affected the quality of food, but also could endanger the consumers' health. The FFA level in 56% of oil samples was lower than the allowable limits (less than 1). In the present study, the lowest and the highest FFA levels in oil samples were estimated as 0.53 and 6.05, respectively.
The p-AV in 45% of the oil samples was lower than 4. The p-AV value was higher than the standard limit (higher than 6) in 34 samples with the mean concentration of 49.87.
We found that the mean TPM values of 54
oil samples were within the regulated limit and
46 samples exceeded the limit value of
25%.
of chemical and physical reactions occur and the
oil undergoes thermal oxidation, polymerization, and hydrolysis. During these reactions, formation
of hydroperoxides and high molecular weight products, such as polar compounds and triacylglycerides increase (Karakaya and Şimşek, 2011). Formation of these polar compounds is related to the primary and secondary oxidation that occurs during frying. Some of these compounds are harmful to human health and contribute to tissue damage, inflammatory diseases, arthrosclerosis, and aging process (Karakaya and Şimşek, 2011). Hydrolytic decomposition occurs after breakage of the triglyceride molecules and leads to the formation of free fatty acids (FFA). The FFA can affect the odor, taste, and other properties of the oil (O'brien, 2008).
One way to identify the oil quality and early stages of oxidation is evaluating the peroxide and FFA levels. The peroxide value measures the total amount of peroxide in oil, as meq of oxygen per kilogram of oil. The FFA level is defined as the number of mg of potassium hydroxide needed to neutralize FFAs in one gram of oil sample. The FFA level is an index for measuring the amount of FFA. Free fatty acids alone are not poisonous but can affect the quality of food (O'brien, 2008). In general, both values are necessary to control the food safety and quality of oils (Gotoh and Wada, 2006). Hydroperoxides, primary products of lipid oxidation, are gradually converted to secondary ones, such as aldehydes, alcohols, carboxylic acids, epoxides, and hydrocarbons (Ruíz and Lendl, 2001). The peroxide value shows the initial stages of oxidation. The peroxide value is measured by weighing the samples, dissolving in chloroform, acidifying by acetic acid, adding potassium
iodide and sample incubation, and then titrating with sodium thiosulfate (Ruíz and Lendl, 2001). The amounts of FFAs produced during the
lipid oxidation can be evaluated by titration
using potassium hydroxide or sodium with phenolphthalein reagent, which is referred to as FFA level (Decker et al., 2010). Frying oils with a FFA level of 1 to 4% are unacceptable. The anisidine value is used for measuring the high molecular weight of saturated and unsaturated compounds in triacylglycerols (Moigradean et al., 2012). Considering the hydrolytic reactions during frying, p-anisidine value (p-AV) could be used as an indicator of oil quality assessment (Farhoosh et al., 2009). Determination of the oxidative breakdown products in frying oils can be measured by total polar compound (TPC) analysis (Sebastian et al., 2014). Productions of the polar compounds have negative effects on frying oil quality, flavor, and nutritional value of fried food (Li et al., 2016). It should be noted that the chemical composition of the frying oil and its physical and chemical properties are important in stability of the oil against oxidation. Therefore, selection of a suitable type of oil for frying is an important problem (Karakaya and Şimşek, 2011). Thermo oxidation reaction due to high temperatures causes extensive chemical and physical changes in oil (Nassehinia and Ahrari, 2016).
Owing to the importance of oil safety and its absorbance by fried foods, the current study attempted to investigate the quality of oils used in fast food shops of Yazd city in 2018.
Materials and Methods
Sampling: In the current descriptive cross-sectional study, 100 oil samples were obtained from fast food shops in Yazd city during spring and summer of 2018. A checklist containing the oil type (oil or fat), odor, color, smoke, and duration of use was prepared and completed at the time of sampling. Samples were collected according to the recommendations provided by Institute of Standards and Industrial Research of Iran (No. 493) (Institute of Standards and Industrial Research of Iran, 2004, Takeoka et al., 1997). Sampling was performed at peak hours (9 to 12 p.m). The collected samples were kept at 5-15 °C until the test was performed.
Peroxide value (PV): Peroxide value was determined based on the standard method (No. 4179) presented by Institute of Standards and Industrial Research of Iran. According to this standard, the permissible PV in fat and oil is 5 and 2 meq/kg, respectively (Institute of Standards and Industrial Research of Iran, 2004). For this purpose, 5 g of oil samples was weighed and 30 ml of acetic acid-chloroform solution (3 to 2) was added. Later, 0.5 ml of the saturated potassium iodide solution was added and placed one minute in the dark. Next, 30 ml of distilled water was added and titrated by sodium thiosulfate (0.1 N) in the presence of starch reagent. The PV (meq/kg) was evaluated according to the equation:
PV = (V-Vb) × N × 1000/W
Where, V and Vb are the volume of used sodium thiosulfate by sample and blank (ml), N is concentration of sodium thiosulfate, and W is the oil weight (g) (Rahimzadeh Barzoki et al., 2013).
Free fatty acid: In order to determine the FFA, 30 ml of the neutral ethanol was added to 5 g of oil and titrated with potassium hydroxide in the presence of phenolphthalein reagent until the pink color appeared and stable. The FFA was evaluated as below:
FFA = 5.611 × N × V/W
Which, N is potassium hydroxide concentration, V is potassium hydroxide volume used for titration (ml), and W is the oil weight (g) (Hassanzadazar et al., 2018, Sebastian et al., 2014).
P-anisidine value: p-anisidine value was evaluated using AOCS Official Method Cd 18-90 method. The oil samples (W: 0.5 g) were diluted with isooctane (25 ml) and absorbance was measured at 350 nm by UV-Visible spectrophotometer (Ab). Later, 5 ml of diluted sample was mixed with 1 ml Anisidine solution (0.25% p-anisidine in acetic acid) and the absorbance was read at 350 nm against isooctane and anisidine solution as blank (As) (American Oil Chemists' Society, 1998, Zhang et al., 2010). The anisidine value was calculated according to the following equation:
Anisidine value = 25 × (1.2As-Ab)/W
Total polar compound (TPC): The TPCs of oil samples were measured by TestoTM 270 cooking oil tester, which showed the changes in dielectric constant of oil related to TPC concentration of oil samples (Song et al., 2017).
Results
As shown in Table 1, about 93% of the samples were oils (in form of liquid). Approximately 45% of the samples had a dark color and about 57% of the samples had an undesirable odor during cooking. As a result, in 23% of the fast food shops, oil was used more than two days.
Table 2 shows the average amount of peroxide and FFA levels in the oils used in fast food shops in Yazd. Among all studied oil samples, peroxide values were higher than the permissible limit in 73 samples. The average permissible peroxide value was estimated as 2.33 meq/kg. In this study, the lowest and highest peroxide values in oil samples were calculated to be 0.56 and 286.49 meq/kg, respectively.
According to the results, most oil samples were oxidized and the production of hydroproxides small volatile molecules, such as aldehydes, ketones, carboxylic acid, and short-chain alkanes not only affected the quality of food, but also could endanger the consumers' health. The FFA level in 56% of oil samples was lower than the allowable limits (less than 1). In the present study, the lowest and the highest FFA levels in oil samples were estimated as 0.53 and 6.05, respectively.
The p-AV in 45% of the oil samples was lower than 4. The p-AV value was higher than the standard limit (higher than 6) in 34 samples with the mean concentration of 49.87.
We found that the mean TPM values of 54
oil samples were within the regulated limit and
46 samples exceeded the limit value of
25%.
| Table 1. Oil characteristics in fast food restaurants in Yazd | ||
| Oil characteristics | % | |
| Type of oil (liquid) | 93 | |
| Presence of smoke during cooking | 4 | |
| Dark color | 45 | |
| Undesirable odor | 57 | |
| Using the oil more than 2 days | 23 | |
| Table 2. The quality assessments of oil sample collected from fast food restaurants in Yazd | ||||
| Tests | Ranges | % | Mean ± SD | |
| Peroxide value (meq/kg) |
Equal or less than 5 | 27 | 2.33 ± 1.29 | |
| 5 to 20 | 47 | 10.77 ± 4.31 | ||
| 21 to 50 | 22 | 28.65 ± 6.25 | ||
| Higher than 50 | 4 | 144.00 ± 92.84 | ||
| Free fatty acid levels (%) |
Equal or Less than 1 | 56 | 0.53 ± 0.22 | |
| 1 to 2 | 37 | 1.37 ± 0.25 | ||
| 2 to 3 | 4 | 2.43 ± 0.33 | ||
| Higher than 3 | 3 | 4.39 ± 1.47 | ||
| Anisidine value |
Equal or Less than 4 | 45 | 2.78 ± 0.54 | |
| 4 to 6 | 21 | 5.16 ± 0.23 | ||
| Higher than 6 | 34 | 49.87 ± 10.34 | ||
| Total polar compound | Equal or Less than 25 | 54 | 21.96 ± 1.76 | |
| Higher than 25 | 46 | 30.54 ± 3.09 | ||
Discussion
In recent years, changes in lifestyle have led to an increase in the consumption of ready-to-eat foods. Deep-fat frying is one of the usual ways to prepare food, which results in the production of desirable or undesirable compounds in fried foods (Farrokhzadeh et al., 2013). The peroxide value is one of the most common methods to measure oxidation in oil. The refined oil usually has a peroxide value of less than 1 meq/kg, so that it reaches up to 10 meq/kg in oxidized oils. According to the literature, vegetable oil with peroxide value of less than 2 meq/kg has good quality to use (Sebastian et al., 2014). The evaluation of p-AV in oils is the accurate and reliable method for determining oil oxidation. The desirable p-AV for fresh oil is less than 4 and oils with p-AV of higher than 6 are considered oxidized (Sebastian et al., 2014). The TPC was introduced as the reliable parameter for determination of the fried oil quality with recommended limit of 25%. Furthermore, application of the rapid assays instead of column chromatography can be suitable in polar components (Song et al., 2017). In present study, the peroxide value, FFA, p-Anisidine value, and TPC of the oil samples were investigated.
The changes in oil (darken oil) during frying, as visible factors, can occur and can be considered as one of the parameters for determining the quality of frying oil (Sebastian et al., 2014). In the present study, 45% of the oils had a dark color. However, it should be noted that the color of the oil is affected by various factors, such as the type of oil and the type of fried foodstuff. Food compounds can react with oils and its degradation products. So, they produce brown colored compounds, such as Maillard products. Since the oil color can be affected by different chemical processes, only considering the oil color to determine its quality is not correct. In fact, oil color should be considered along with other diagnostic parameters (Takeoka et al., 1997). On the other hand, about 57% of the oil samples were odorless.
In current study, among all the investigated oil samples, 73% had peroxide values of higher than the permissible limit. The peroxide values in
non-consumable oils varied from 10.77 to 144 meq/kg, which indicated extensive oxidation in oil samples. The results of Jahed et al. showed that about 60% and 65% of the oil used in sandwich and falafel shops had peroxide values of higher than the allowable limit, respectively. The highest amount of peroxide values in sandwich and falafel samples was reported 29.79 and 31.22 meq/kg, respectively (Jahed Khaniki et al., 2018), which is lower than results of the current study. Rahimzadeh et al. indicated that 58.3% of the restaurants and 97.3% of sandwich shops in Gorgan City had a higher peroxide value (Rahimzadeh Barzoki et al., 2013). The results of Farrokhzadeh et al. on the residual and consumed oils in the products prepared in delicatessens and confectioneries of Shahinshahr and Meymeh County indicated a high percentage of peroxide value in 27.3% of the oil samples (Farrokhzadeh et al., 2017). Nafez et al. reported that 59% of the fast food shops oils in Kermanshah City were consumable and 41% were unusable containing values higher than the standard limits. The highest and lowest amounts of the peroxide values were reported as 29 and 0 meq/kg, respectively (Nafez et al., 2018), which is considered to have better quality rather than oil samples of the current research. Determination of the peroxides values in the oil used in restaurants and sandwich shops in Yasuj city showed that the peroxide value exceeded the standard limit in 58.3% and 97.3% of the samples, respectively (Pourmahmoudi et al., 2008). Arbabi investigated the oils used in sandwich shops in Shahrekord and stated that in all samples, the peroxide value was higher than the standard limit (Arbabi and Deris, 2011). The same research in Ilam indicated that 61.03% of the oil samples had peroxide value higher than the standard limits (Amarlooei et al., 2013). It was also found that prolonged use of oil (more than two days) resulted in an increase in peroxide values, which is consistent with the results of Amarlooei et al. (Amarlooei et al., 2013).The presence of oxygen and water increases the process of decomposition of frying oil. The lowest and highest peroxide values in oil samples were 0.56 and 286.49 meq/kg, respectively. In Hassanzadazar et al. study on oil samples collected from fast food centers in Zanjan city, the lowest and highest peroxide values were 1.2 and 298.2 meq/kg, respectively (Hassanzadazar et al., 2018).
The temperature and duration of frying, type of oil, and presence of antioxidants in oil can affect the production of undesirable compounds in the oil (Farrokhzadeh et al., 2013). In the present study, 42% of the samples had FFA above the standard limits (upper than 1 %). Study on used oils of the confectioneries and food shops in Borkhar and Meymeh showed that the FFA was higher than standard limits in 7.4% of samples, However, 98.1% of the oil samples were non-consumable (Pourmahmoudi et al., 2008). Sebastian et al. examined the quality and safety of the frying oils used by restaurants. The results showed that 30 to 35% of the used oils and 45 to 55% of the discarded oil samples contained high FFA level, which were not acceptable (Sebastian et al., 2014).
It should be noted that the primary oxidation products are rapidly broken down into secondary ones; thus, it is hard to estimate their total amounts in the oil. Various methods exist for detecting oil oxidations, which is detectable by observation, such as color, smoke, odor, and taste (Sebastian et al., 2014). Except for p-AV value, other analyses are suitable to show the primary oxidation and hydrolysis stage of oil degradation (Sebastian et al., 2014). The mean concentration of p-AV values higher than 6 in oils were estimated as 49.87, which is correlated with the decomposition products such as aldehydes in frying oil (Houhoula et al., 2002). In Sebastian research, all discarded oils were extremely oxidized based on the p-AV value (7.6 to 56.5) (Sebastian et al., 2014). In The current study, about 34% of the oil samples had p-AV values higher than 6.
We found that 54% of the oil used in Yazd restaurants had relatively low TPC levels and 46% of the oils were unacceptable for further use. Andrikopoulos et al. investigated the frying oils of 63 restaurants in Greece. They indicated that 17% of samples had TPC level of higher than 25% (Andrikopoulos et al., 2003). The TPC of the collected oil samples from fast food restaurants in Shiraz was higher than the permitted levels in 45.2% of the samples (Ghobadi et al., 2018). It was shown that the total polar content increased during heating, which is correlated with the number and days of frying (Houhoula et al., 2002). The mean TPC of 16.13% and 15.5 % were reported in the studies by Yilmaz et al. and Sebastian et al., respectively (Sebastian et al., 2014, Yılmaz and Buket, 2011), which is lower than results of our study. The oxidation in frying oil resulted from water and air would increase
the number of polar molecules (Innawong
et al., 2004).
Therefore, the high peroxide and p-AV in the oil samples can be attributed to the long-term use of these materials, high-temperature heating,
and oxygen contact. During frying, the oil
is hydrolyzed and produces FFAs, mono, and diglycerides, which are added to the oil in prolonged uses. In addition, oxidized oil produces hydroperoxide, epoxides, hydroxides, and ketones. Increasing these volatile compounds leads to an increase in the amount of FFA and the peroxide values in the oil samples (Innawong et al., 2004). During the cooling period in frequent uses of fried oil, oxygen can be dissolved in oil and accelerate oxidizing reactions (Ghobadi et al., 2018). In addition, the type of oil (fatty acid composition), heat and frying time, light, and concentration of oxygen during storage, lack of daily washing of the food utensils, and burning the remaining oils can also lead to a rise in oil oxidation (Ghobadi et al., 2018, Nafez et al., 2018). Presence of double bonds in fatty acid chains of oil makes it more susceptible to oxidation. Along with oil type, the type of fried food can have effects on acceleration of the oil degradation (Ghobadi et al., 2018). Production of dangerous materials in fried oil can be important threats for not only the fried food consumers, but also for the fast food restaurant workers who exhale vapor and volatile compounds (Ghobadi et al., 2018). According to Table 1, approximately 23% of the restaurant owners did not change their oil for more than 2 days. In addition to this fact, oils are used about 3 to 5 hours daily; so, deterioration of oils is expected. Therefore, frequent refilling or changing of oils in fast food restaurants can increase the safety of consumed fried foods.
Conclusion
The study found that a large number of fast food shops in Yazd used highly oxidized oils to prepare their food. In addition, due to absorption of frying oils by fried foods, the degradation of frying oil can be hazardous for the consumers’ safety and endangers the population's health. Overall, the fried foods are considered unsafe since they increase the rate of obesity, diabetes type 2, and cardiovascular diseases. So, continuous monitoring of the fast food restaurants for production of healthy foods as well as training the fast-food
staff seem necessary.
Authors’ contribution
Khalili N, Akrami Mohajeri F, and Khalili Sadrabad E conceived and designed the experiments. Ramroudi F, Mojaver F, Hakimi F, Sardari M, and Khebri M carried out the experiment. All authors contributed to the final version of the manuscript.
Acknowledgment:
This manuscript was financially supported by Shahid Sadoughi University of Medical Sciences, school of public health, Yazd, Iran.
Conflict of interest
There is no conflict of interest.
References
In recent years, changes in lifestyle have led to an increase in the consumption of ready-to-eat foods. Deep-fat frying is one of the usual ways to prepare food, which results in the production of desirable or undesirable compounds in fried foods (Farrokhzadeh et al., 2013). The peroxide value is one of the most common methods to measure oxidation in oil. The refined oil usually has a peroxide value of less than 1 meq/kg, so that it reaches up to 10 meq/kg in oxidized oils. According to the literature, vegetable oil with peroxide value of less than 2 meq/kg has good quality to use (Sebastian et al., 2014). The evaluation of p-AV in oils is the accurate and reliable method for determining oil oxidation. The desirable p-AV for fresh oil is less than 4 and oils with p-AV of higher than 6 are considered oxidized (Sebastian et al., 2014). The TPC was introduced as the reliable parameter for determination of the fried oil quality with recommended limit of 25%. Furthermore, application of the rapid assays instead of column chromatography can be suitable in polar components (Song et al., 2017). In present study, the peroxide value, FFA, p-Anisidine value, and TPC of the oil samples were investigated.
The changes in oil (darken oil) during frying, as visible factors, can occur and can be considered as one of the parameters for determining the quality of frying oil (Sebastian et al., 2014). In the present study, 45% of the oils had a dark color. However, it should be noted that the color of the oil is affected by various factors, such as the type of oil and the type of fried foodstuff. Food compounds can react with oils and its degradation products. So, they produce brown colored compounds, such as Maillard products. Since the oil color can be affected by different chemical processes, only considering the oil color to determine its quality is not correct. In fact, oil color should be considered along with other diagnostic parameters (Takeoka et al., 1997). On the other hand, about 57% of the oil samples were odorless.
In current study, among all the investigated oil samples, 73% had peroxide values of higher than the permissible limit. The peroxide values in
non-consumable oils varied from 10.77 to 144 meq/kg, which indicated extensive oxidation in oil samples. The results of Jahed et al. showed that about 60% and 65% of the oil used in sandwich and falafel shops had peroxide values of higher than the allowable limit, respectively. The highest amount of peroxide values in sandwich and falafel samples was reported 29.79 and 31.22 meq/kg, respectively (Jahed Khaniki et al., 2018), which is lower than results of the current study. Rahimzadeh et al. indicated that 58.3% of the restaurants and 97.3% of sandwich shops in Gorgan City had a higher peroxide value (Rahimzadeh Barzoki et al., 2013). The results of Farrokhzadeh et al. on the residual and consumed oils in the products prepared in delicatessens and confectioneries of Shahinshahr and Meymeh County indicated a high percentage of peroxide value in 27.3% of the oil samples (Farrokhzadeh et al., 2017). Nafez et al. reported that 59% of the fast food shops oils in Kermanshah City were consumable and 41% were unusable containing values higher than the standard limits. The highest and lowest amounts of the peroxide values were reported as 29 and 0 meq/kg, respectively (Nafez et al., 2018), which is considered to have better quality rather than oil samples of the current research. Determination of the peroxides values in the oil used in restaurants and sandwich shops in Yasuj city showed that the peroxide value exceeded the standard limit in 58.3% and 97.3% of the samples, respectively (Pourmahmoudi et al., 2008). Arbabi investigated the oils used in sandwich shops in Shahrekord and stated that in all samples, the peroxide value was higher than the standard limit (Arbabi and Deris, 2011). The same research in Ilam indicated that 61.03% of the oil samples had peroxide value higher than the standard limits (Amarlooei et al., 2013). It was also found that prolonged use of oil (more than two days) resulted in an increase in peroxide values, which is consistent with the results of Amarlooei et al. (Amarlooei et al., 2013).The presence of oxygen and water increases the process of decomposition of frying oil. The lowest and highest peroxide values in oil samples were 0.56 and 286.49 meq/kg, respectively. In Hassanzadazar et al. study on oil samples collected from fast food centers in Zanjan city, the lowest and highest peroxide values were 1.2 and 298.2 meq/kg, respectively (Hassanzadazar et al., 2018).
The temperature and duration of frying, type of oil, and presence of antioxidants in oil can affect the production of undesirable compounds in the oil (Farrokhzadeh et al., 2013). In the present study, 42% of the samples had FFA above the standard limits (upper than 1 %). Study on used oils of the confectioneries and food shops in Borkhar and Meymeh showed that the FFA was higher than standard limits in 7.4% of samples, However, 98.1% of the oil samples were non-consumable (Pourmahmoudi et al., 2008). Sebastian et al. examined the quality and safety of the frying oils used by restaurants. The results showed that 30 to 35% of the used oils and 45 to 55% of the discarded oil samples contained high FFA level, which were not acceptable (Sebastian et al., 2014).
It should be noted that the primary oxidation products are rapidly broken down into secondary ones; thus, it is hard to estimate their total amounts in the oil. Various methods exist for detecting oil oxidations, which is detectable by observation, such as color, smoke, odor, and taste (Sebastian et al., 2014). Except for p-AV value, other analyses are suitable to show the primary oxidation and hydrolysis stage of oil degradation (Sebastian et al., 2014). The mean concentration of p-AV values higher than 6 in oils were estimated as 49.87, which is correlated with the decomposition products such as aldehydes in frying oil (Houhoula et al., 2002). In Sebastian research, all discarded oils were extremely oxidized based on the p-AV value (7.6 to 56.5) (Sebastian et al., 2014). In The current study, about 34% of the oil samples had p-AV values higher than 6.
We found that 54% of the oil used in Yazd restaurants had relatively low TPC levels and 46% of the oils were unacceptable for further use. Andrikopoulos et al. investigated the frying oils of 63 restaurants in Greece. They indicated that 17% of samples had TPC level of higher than 25% (Andrikopoulos et al., 2003). The TPC of the collected oil samples from fast food restaurants in Shiraz was higher than the permitted levels in 45.2% of the samples (Ghobadi et al., 2018). It was shown that the total polar content increased during heating, which is correlated with the number and days of frying (Houhoula et al., 2002). The mean TPC of 16.13% and 15.5 % were reported in the studies by Yilmaz et al. and Sebastian et al., respectively (Sebastian et al., 2014, Yılmaz and Buket, 2011), which is lower than results of our study. The oxidation in frying oil resulted from water and air would increase
the number of polar molecules (Innawong
et al., 2004).
Therefore, the high peroxide and p-AV in the oil samples can be attributed to the long-term use of these materials, high-temperature heating,
and oxygen contact. During frying, the oil
is hydrolyzed and produces FFAs, mono, and diglycerides, which are added to the oil in prolonged uses. In addition, oxidized oil produces hydroperoxide, epoxides, hydroxides, and ketones. Increasing these volatile compounds leads to an increase in the amount of FFA and the peroxide values in the oil samples (Innawong et al., 2004). During the cooling period in frequent uses of fried oil, oxygen can be dissolved in oil and accelerate oxidizing reactions (Ghobadi et al., 2018). In addition, the type of oil (fatty acid composition), heat and frying time, light, and concentration of oxygen during storage, lack of daily washing of the food utensils, and burning the remaining oils can also lead to a rise in oil oxidation (Ghobadi et al., 2018, Nafez et al., 2018). Presence of double bonds in fatty acid chains of oil makes it more susceptible to oxidation. Along with oil type, the type of fried food can have effects on acceleration of the oil degradation (Ghobadi et al., 2018). Production of dangerous materials in fried oil can be important threats for not only the fried food consumers, but also for the fast food restaurant workers who exhale vapor and volatile compounds (Ghobadi et al., 2018). According to Table 1, approximately 23% of the restaurant owners did not change their oil for more than 2 days. In addition to this fact, oils are used about 3 to 5 hours daily; so, deterioration of oils is expected. Therefore, frequent refilling or changing of oils in fast food restaurants can increase the safety of consumed fried foods.
Conclusion
The study found that a large number of fast food shops in Yazd used highly oxidized oils to prepare their food. In addition, due to absorption of frying oils by fried foods, the degradation of frying oil can be hazardous for the consumers’ safety and endangers the population's health. Overall, the fried foods are considered unsafe since they increase the rate of obesity, diabetes type 2, and cardiovascular diseases. So, continuous monitoring of the fast food restaurants for production of healthy foods as well as training the fast-food
staff seem necessary.
Authors’ contribution
Khalili N, Akrami Mohajeri F, and Khalili Sadrabad E conceived and designed the experiments. Ramroudi F, Mojaver F, Hakimi F, Sardari M, and Khebri M carried out the experiment. All authors contributed to the final version of the manuscript.
Acknowledgment:
This manuscript was financially supported by Shahid Sadoughi University of Medical Sciences, school of public health, Yazd, Iran.
Conflict of interest
There is no conflict of interest.
References
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American Oil Chemists' Society 1998. Official methods and recommended practices of the American Oil Chemists' Society. AOCS: USA.
Andrikopoulos NK, et al. 2003. Quality assessment of frying oils and fats from 63 restaurants in Athens, Greece. Food Service Technology. 3 (2): 49-59.
Arbabi M & Deris F 2011. Determination of hydrogen peroxide index in the consumption edible oils in fast food shops. Journal of Shahrekord Uuniversity of Medical Sciences. 13 (3): 90-99.
Decker EA, Elias RJ & McClements DJ 2010. Oxidation in foods and beverages and antioxidant applications: management in different industry sectors. Elsevier.
Farhoosh R, Esmaeilzadeh Kenari R & Poorazrang H 2009. Frying stability of canola oil blended with palm olein, olive, and corn oils. Journal of the American Oil Chemists' Society. 86 (1): 71-76.
Farrokhzadeh H, et al. 2013. Measurement of used oil rancidity indexes in the confectioneries and food shops. International Journal of Environmental Health Engineering. 2 (1): 28.
Farrokhzadeh H, Ghorbani E, Shahrajabian N & Hassanzadeh A 2017. Qualitative Investigation of the Consumed and Residual Oils in Food Products Prepared in Delicatessens and Confectioneries of Shahinshahr and Meymeh County, Iran. Journal of Health System Research. 13 (3): 312-316.
Ghobadi S, Akhlaghi M, Shams S & Mazloomi SM 2018. Acid and peroxide values and total polar compounds of frying oils in fast food restaurants of Shiraz, Southern Iran. International Journal of Nutrition Sciences. 3 (1): 25-30.
Gotoh N & Wada S 2006. The importance of peroxide value in assessing food quality and food safety. Journal of the American Oil Chemists' Society. 83 (5): 473-474.
Hassanzadazar H, Ghayurdoost F, Aminzare M, Mottaghianpour E & Taami B 2018. Monitoring of Edible Oils Quality in Restaurants and Fast Food Centers Using Peroxide and Acid Values. Journal of Chemical Health Risks. 8 ( 3): 217-222.
Houhoula DP, Oreopoulou V & Tzia C 2002. A kinetic study of oil deterioration during frying and a comparison with heating. Journal of the American Oil Chemists' Society. 79 (2): 133-137.
Innawong B, Mallikarjunan P, Irudayaraj J & Marcy JE 2004. The determination of frying oil quality using Fourier transform infrared attenuated total reflectance. LWT-Food Science and Technology. 37 (1): 23-28.
Institute of Standards and Industrial Research of Iran 2004. No. 493, 4179. Tehran, Iran: ISIR. In Edible fats and oils sampling.
Jahed Khaniki G, Safaei P, Barik Gugjlu R & Mohajer A 2018. Determination of peroxide value of edible oils used in sandwich and falafel shops in Tehran. Iranian Journal of Health & Environment. 10 (4).
Karakaya S & Şimşek Ş 2011. Changes in total polar compounds, peroxide value, total phenols and antioxidant activity of various oils used in deep fat frying. Journal of the American Oil Chemists' Society. 88 (9): 1361-1366.
Li J, Cai W, Sun D & Liu Y 2016. A quick method for determining total polar compounds of frying oils using electric conductivity. Food Analytical Methods. 9 (5): 1444-1450.
Moigradean D, Poiana M-A & Gogoasa I 2012. Quality characteristics and oxidative stability of coconut oil during storage. Journal of Agroalimentary Processes and Technologies. 18 (4): 272-276.
Nafez AH, et al. 2018. Evaluation of Peroxide Amount in the Consumed Oil Used in the Fast Food Shops of Kermanshah City, Iran, in the Year 2016. Journal of Health System Research. 13 (4): 399-404.
Nassehinia H & Ahrari F 2016. Determination of peroxide value of oils used in the confectioneries of Damghan, Iran in spring 2015. Journal of Health Research in Community. 1 (4): 64-69.
O'brien RD 2008. Fats and oils: formulating and processing for applications. CRC press.
Pourmahmoudi A, Akbartabar Turi M, Poursamad A, Sadat A & Karimi A 2008. Determination of peroxide value of edible oils used in restaurants and sandwich shops in Yasuj in 2006. Armaghane Danesh. 13 (1): 115-123.
Rahimzadeh Barzoki H, et al. 2013. Determination of Peroxide Value of Edible Oils Used in Confectionary, Restaurants and Sandwich Shops in Gorgan in 2011. Journal of Toloo e Behdasht. 13 (1): 40-47.
Ruíz A & Lendl B 2001. A rapid method for peroxide value determination in edible oils based on flow analysis with Fourier transform infrared spectroscopic detection. Analyst. 126 (2): 242-246.
Sebastian A, Ghazani SM & Marangoni AG 2014. Quality and safety of frying oils used in restaurants. Food Research International. 64:
420-423.
Song J, Kim M-J, Kim Y-J & Lee J 2017. Monitoring changes in acid value, total polar material, and antioxidant capacity of oils used for frying chicken. Food Chemistry. 220: 306-312.
Takeoka GR, Full GH & Dao LT 1997. Effect of heating on the characteristics and chemical composition of selected frying oils and fats. Journal of Agricultural and Food Chemistry. 45 (8): 3244-3249.
Yılmaz E & Buket A 2011. Quantitative assessment of frying oil quality in fast food restaurants. GIDA. 36 (3): 121-127.
Zhang Y, et al. 2010. Oxidative stability of sunflower oil supplemented with carnosic acid compared with synthetic antioxidants during accelerated storage. Food Chemistry. 118 (3): 656-662.
American Oil Chemists' Society 1998. Official methods and recommended practices of the American Oil Chemists' Society. AOCS: USA.
Andrikopoulos NK, et al. 2003. Quality assessment of frying oils and fats from 63 restaurants in Athens, Greece. Food Service Technology. 3 (2): 49-59.
Arbabi M & Deris F 2011. Determination of hydrogen peroxide index in the consumption edible oils in fast food shops. Journal of Shahrekord Uuniversity of Medical Sciences. 13 (3): 90-99.
Decker EA, Elias RJ & McClements DJ 2010. Oxidation in foods and beverages and antioxidant applications: management in different industry sectors. Elsevier.
Farhoosh R, Esmaeilzadeh Kenari R & Poorazrang H 2009. Frying stability of canola oil blended with palm olein, olive, and corn oils. Journal of the American Oil Chemists' Society. 86 (1): 71-76.
Farrokhzadeh H, et al. 2013. Measurement of used oil rancidity indexes in the confectioneries and food shops. International Journal of Environmental Health Engineering. 2 (1): 28.
Farrokhzadeh H, Ghorbani E, Shahrajabian N & Hassanzadeh A 2017. Qualitative Investigation of the Consumed and Residual Oils in Food Products Prepared in Delicatessens and Confectioneries of Shahinshahr and Meymeh County, Iran. Journal of Health System Research. 13 (3): 312-316.
Ghobadi S, Akhlaghi M, Shams S & Mazloomi SM 2018. Acid and peroxide values and total polar compounds of frying oils in fast food restaurants of Shiraz, Southern Iran. International Journal of Nutrition Sciences. 3 (1): 25-30.
Gotoh N & Wada S 2006. The importance of peroxide value in assessing food quality and food safety. Journal of the American Oil Chemists' Society. 83 (5): 473-474.
Hassanzadazar H, Ghayurdoost F, Aminzare M, Mottaghianpour E & Taami B 2018. Monitoring of Edible Oils Quality in Restaurants and Fast Food Centers Using Peroxide and Acid Values. Journal of Chemical Health Risks. 8 ( 3): 217-222.
Houhoula DP, Oreopoulou V & Tzia C 2002. A kinetic study of oil deterioration during frying and a comparison with heating. Journal of the American Oil Chemists' Society. 79 (2): 133-137.
Innawong B, Mallikarjunan P, Irudayaraj J & Marcy JE 2004. The determination of frying oil quality using Fourier transform infrared attenuated total reflectance. LWT-Food Science and Technology. 37 (1): 23-28.
Institute of Standards and Industrial Research of Iran 2004. No. 493, 4179. Tehran, Iran: ISIR. In Edible fats and oils sampling.
Jahed Khaniki G, Safaei P, Barik Gugjlu R & Mohajer A 2018. Determination of peroxide value of edible oils used in sandwich and falafel shops in Tehran. Iranian Journal of Health & Environment. 10 (4).
Karakaya S & Şimşek Ş 2011. Changes in total polar compounds, peroxide value, total phenols and antioxidant activity of various oils used in deep fat frying. Journal of the American Oil Chemists' Society. 88 (9): 1361-1366.
Li J, Cai W, Sun D & Liu Y 2016. A quick method for determining total polar compounds of frying oils using electric conductivity. Food Analytical Methods. 9 (5): 1444-1450.
Moigradean D, Poiana M-A & Gogoasa I 2012. Quality characteristics and oxidative stability of coconut oil during storage. Journal of Agroalimentary Processes and Technologies. 18 (4): 272-276.
Nafez AH, et al. 2018. Evaluation of Peroxide Amount in the Consumed Oil Used in the Fast Food Shops of Kermanshah City, Iran, in the Year 2016. Journal of Health System Research. 13 (4): 399-404.
Nassehinia H & Ahrari F 2016. Determination of peroxide value of oils used in the confectioneries of Damghan, Iran in spring 2015. Journal of Health Research in Community. 1 (4): 64-69.
O'brien RD 2008. Fats and oils: formulating and processing for applications. CRC press.
Pourmahmoudi A, Akbartabar Turi M, Poursamad A, Sadat A & Karimi A 2008. Determination of peroxide value of edible oils used in restaurants and sandwich shops in Yasuj in 2006. Armaghane Danesh. 13 (1): 115-123.
Rahimzadeh Barzoki H, et al. 2013. Determination of Peroxide Value of Edible Oils Used in Confectionary, Restaurants and Sandwich Shops in Gorgan in 2011. Journal of Toloo e Behdasht. 13 (1): 40-47.
Ruíz A & Lendl B 2001. A rapid method for peroxide value determination in edible oils based on flow analysis with Fourier transform infrared spectroscopic detection. Analyst. 126 (2): 242-246.
Sebastian A, Ghazani SM & Marangoni AG 2014. Quality and safety of frying oils used in restaurants. Food Research International. 64:
420-423.
Song J, Kim M-J, Kim Y-J & Lee J 2017. Monitoring changes in acid value, total polar material, and antioxidant capacity of oils used for frying chicken. Food Chemistry. 220: 306-312.
Takeoka GR, Full GH & Dao LT 1997. Effect of heating on the characteristics and chemical composition of selected frying oils and fats. Journal of Agricultural and Food Chemistry. 45 (8): 3244-3249.
Yılmaz E & Buket A 2011. Quantitative assessment of frying oil quality in fast food restaurants. GIDA. 36 (3): 121-127.
Zhang Y, et al. 2010. Oxidative stability of sunflower oil supplemented with carnosic acid compared with synthetic antioxidants during accelerated storage. Food Chemistry. 118 (3): 656-662.
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Received: 2019/02/2 | Published: 2020/07/27 | ePublished: 2020/07/27
Received: 2019/02/2 | Published: 2020/07/27 | ePublished: 2020/07/27
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