Deep frying is the process of immersing food in hot oil at a temperature of approximately
180°C. During deep frying, different chemical reactions are taking place, resulting in
changes in the ...physicochemical properties of the frying oil, eventually leading to harmful
health effects on the consumers. Nevertheless, based on economic feasibility, both the
domestic and industrial levels tend to repeatedly use edible oils for deep frying. Thus, the
current study aimed to evaluate physicochemical and nutritional parameters of
commercially available coconut oil, palm oil and sunflower oil and to investigate the
effect of repeated deep frying for the physicochemical and nutritional parameters of the
studied oil samples. Thereby, the optimum number of frying cycles for each type of oil
was also investigated. In order to achieve that, using coconut, palm and sunflower oils,
potato and fish were fried separately for five repeated frying cycles. As per the results,
regardless of the frying material, the relative density, colour, peroxide value, free fatty
acid value of coconut oil, palm oil, and sunflower oil were increased significantly with
increase the number of frying cycles whereas the smoke point and moisture content was
found to be significantly decreased. In contrast, the number of cycles suitable for repeated
frying is varying upon the frying material. Accordingly, coconut oil has proven to be used
for three frying cycles of potato and five frying cycles of fish: palm oil for one frying of
potato and two fryings of fish without adversely altering their physicochemical and
nutritional properties. Conferring to the obtained results, the use of unsaturated oil like
sunflower oil on repeated frying is not recommended.
•Higher UFP, PM2.5 and PAHs exposure in cookers.•Urinary 1-OHP, MDA and 8-OHdG reflect COFs exposure.•RFO may cause increased oxidative DNA damage.•RWO may cause increased lipid peroxidation.
To ...evaluate how exposure to deep-frying oils, repeated frying oil (RFO) and restaurant waste oil (RWO) affects emission of polycyclic aromatic hydrocarbons (PAHs) and oxidative stress in male restaurant workers.
The study participants included 236 male restaurant workers in 12 restaurants in Shenzhen. Airborne particulate PAHs were measured over 12h on each of two consecutive work days. Urinary 1-hydroxypyrene (1-OHP) measurements were used to indicate cooking oil fumes (COF) exposure, and urinary malondialdehyde (MDA) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) were adopted as oxidative stress markers.
The production and emission rates of ultrafine particles (UFPs) and PM2.5 were higher in the exposed groups than in the control group. The concentrations of summed PAHs were in the order of RFO-frying group>RWO-frying group>deep-frying group>unexposed control group. Urinary 1-OHP was found to be a significant predictor of elevated urinary MDA and 8-OHdG concentrations (all, P<0.05). UFPs were a significant predictor of elevated urinary 8-OHdG for restaurant workers (P<0.05). The RFO- and RWO-frying groups had higher mean urinary concentrations of 1-OHP, MDA and 8-OHdG than the control group (P<0.05). RFO exposure was found to be a significant risk factor for elevated urinary 8-OHdG and RWO exposure was found to be a significant risk factor for elevated urinary MDA (both, P<0.001).
Concentrations of urinary 1-OHP, MDA and 8-OHdG reflect occupational exposure to PAHs from COFs and oxidative stress in restaurants workers. Exposure to RFO may cause increased oxidative DNA damage, and exposure to RWO might cause increased lipid peroxidation.
The aim of this study was to compare thermal degradation of oil, especially the composition of the polymer in a polar and nonpolar fraction of oil, used for repeated frying of fast and traditional ...French fries. The French fries were fried using the partially hydrogenated rapeseed oil. Fast French fries were characterized by a half shorter frying time compared to traditional ones. The frying process was done at 170 °C ± 5 °C in 5‐l electric fryers and carried out in 15‐min cycles for 48 hours. The content of thermal decomposition of triacylglycerol (TAG) in both fractions of oil was analyzed by high‐performance size‐exclusion chromatography (HPSEC). In all analyzed samples, thermal decomposition products were found. However, the composition of a polar and nonpolar fraction of oil was not the same. In a nonpolar fraction, only the monomers and hydrolysis products of TAG were observed. In a polar fraction, dimers, trimers, and oligomers of TAG were also found. The shorter time of frying the fast French fries resulted in a lower total and individual polymers content in all steps of analysis compared to the oil used for frying the traditional French fries.
Fried dietary oils often cause adverse health effects due to altered chemical and nutritional properties. In the present study with mustard oil, the effect of repeated frying (180°C for 10 min, three ...times) on chemical characteristics and oral intake of raw and fried mustard oil (5 g/kg for 5 weeks) in Wistar rats were investigated. Repeated frying caused oxidation reactions and free fatty acid content in mustard oil. This fried oil feeding to rats increased serum LDL cholesterol and triglycerides and decreased HDL leading to nonalcoholic fatty liver disease accounted by significant increment of liver enzymes (ALT, AST, ALP) compared with raw oil‐fed group. Higher level of serum CK‐MB and creatinine in fried oil‐fed rats indicate disrupted kidney function. Histological findings of the respective organs ascertained metabolic abnormalities due to fried oil intake. Thus, the study suggests avoidance of using repeatedly fried oils in food products for better consumer health.
Practical applications
Vegetable oil is a common ingredient of food products. Mustard oil is used in many countries both as raw and fried forms for various food preparations. When it is being fried at elevated temperatures in the presence of air, both thermal and oxidative decomposition take place which alter the nutritional and functional bioactive properties of the oil. The findings of the current study revealed the repeatedly fried mustard oil‐induced detrimental effects on various organs of Wistar rats. Human beings consuming repeatedly fried mustard oil regularly might also face these acute problems. Thus in context to the public health issue, it is a message to avoid in taking repeated fried oils at household cooking or food industry to maintain better health.
Repeated frying caused formation of free fatty acids in the mustard oil. Consumption of the repeatedly fried mustard oil caused altered lipid metabolism in Wistar rats. The elevated level of serum biomarkers denoting to cardiovascular disease, nonalcoholic fatty liver disease and glomerulosclerosis were also ascertained by histological findings of respective organs.
Summary
This work focuses on the effect of frying variables (repeated frying, potato‐to‐oil ratio, potato distribution in the fryer, oil type and potato variety) on French fry properties (water ...content, oil content, crust thickness and shrinkage). Furthermore, the rate of change in French fry properties during a frying batch is investigated. The temperature was acquired in several positions within the oil and the potato. It was found that when repeated frying was conducted up to regulation limits for frying oil use, the examined French fry properties were not significantly affected. On the contrary, the potato‐to‐oil ratio, potato distribution and potato variety significantly affected the water content of French fries. The most significant changes occurred during the first 1–2 min of a frying batch. According to the temperature measurements, the crust‐core front continued to advance after this first frying period. However, there was no observable crust thickness increase; this was attributed to crust shrinkage.
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