Effect of Bene Kernel Oil on the Frying Stability of Canola Oil

Canola oil (CAO) with (0.05–0.4%) and without added bene kernel oil (BKO) and tert-butylhydroquinone (TBHQ, 100 ppm) was used for deep-fat frying of potatoes at 180 °C for 48 h. Frying stability of the oil samples during the frying process was measured based on the variations of total polar compounds (TPC) content, conjugated diene value (CDV), acid value (AV), carbonyl value (CV) and total tocopherols (TT). In general, frying stability of the CAO significantly (P < 0.05) improved in the presence of the TBHQ and BKO. The best frying performance for the CAO was obtained by using of 100 ppm TBHQ and 0.1% BKO. The effectiveness of TBHQ and BKO at these levels was found to be nearly the same. Increasing the level of BKO from 0.1 to 0.4% caused a decrease in the oxidative stability of the CAO, indicating the pro-oxidant effect of the oils added at these levels.     

Formation and distribution of oxidized fatty acids during deep‐ and pan‐frying of potatoes

The formation of cis‐9,10‐epoxystearate, trans‐9,10‐epoxystearate, cis‐9,10‐epoxyoleate, cis‐12,13‐epoxyoleate, trans‐9,10‐epoxyoleate, trans‐12,13‐epoxyoleate and the co‐eluting 9‐ and 10‐ketostearates during eight successive pan‐ and deep‐frying sessions of pre‐fried potatoes in five different types of vegetable oils – namely cottonseed oil, sunflower oil, vegetable shortening, palm oil and virgin olive oil – was followed and quantified both in fried oils and in fried potatoes by GC/MS after derivatization to methyl esters. These oxidized fatty acids were present at relatively low concentrations in the fresh oils and pre‐fried potatoes while they increased linearly with frying time, reaching up to 1140.8 µg/g in virgin olive oil (VOO) and 186.9 µg/g in potatoes pan‐fried in VOO after eight pan‐frying sessions, with trans‐9,10‐epoxystearate predominating in all cases. The formation of polymerized triacylglycerols (PTG) was also quantified in frying oils by size exclusion HPLC. Pan‐frying caused higher oxidized fatty acid and PTG formation compared to deep‐frying. Epoxyoleates and PTG concentrations were increased after frying in polyunsaturated oils, while epoxystearate and 9‐ and 10‐ketostearate concentrations were increased after frying in monounsaturated oils. No specific absorption of the oxidized fatty acids by the fried potatoes seems to occur. The dietary intake of oxidized fatty acids and PTG by the consumption of fried potatoes was discussed.     

Antioxidative Properties of <Emphasis Type="Italic">Curcuma longa</Emphasis> Leaf Extract in Accelerated Oxidation and Deep Frying Studies

The antioxidative properties of Curcuma longa (turmeric) leaf extract were evaluated in refined, bleached and deodorized (RBD) palm olein using accelerated oxidation and deep frying studies at 180 °C for up to 40 h. The extract was capable of retarding oil oxidation and deterioration significantly (P < 0.05) at 0.2% concentration, better than 0.02% BHT for the Oxidative Stability Index (OSI) in an accelerated oxidation study and also the peroxide value in deep frying studies. In sensory evaluation, the French fries were acceptable and were not significantly different (P < 0.05) from one another for color, oiliness and crispiness throughout the 40-h frying study. Curcuma longa leaf extract, which had a polyphenol content of 116.3 ± 0.2 mg/g, possessed heat-stable antioxidant properties and may be a good natural alternative to existing synthetic antioxidants in the food industry.     

Monitoring of 2,4‐decadienal in oils and fats used for frying in restaurants in Athens,Greece

Some frying by‐products of medium polarity, so‐called medium‐polarity materials (MPM), produced during domestic deep‐frying of French‐fried potatoes in edible vegetable oils, have recently been isolated and linearly correlated to % total polar materials and % polymerized triglycerides. The in vitro oxidation of low‐density lipoproteins in a dose‐dependent manner by MPM has also been reported. In the present study, the MPM constituents were identified after extraction of MPM from the oils, subsequent purification by RP‐HPLC, and GC‐MS analysis. The main constituent of MPM was trans,trans‐2,4‐decadienal, a compound that has previously been reported to be formed during peroxidation of linoleic and arachidonic acid. 2,4‐Decadienal was also quantified in oils and fats used for frying in restaurants in Athens, Greece, by direct injection of oil sample solutions in HPLC. For the most commonly used frying oils, 2,4‐decadienal concentration ranges were 0.3–119.7 mg/kg for sunflower oil, 13.3–92.7 mg/kg for cottonseed oil, 4.1–44.9 mg/kg for palm oil, and 2.0–11.3 mg/kg for vegetable cooking fats. Considering the common catering practices of frying, 2,4‐decadienal was more likely to be found in sunflower oil after deep‐frying of potatoes. Comparing the amounts of this aldehyde found in oils from restaurants to the amounts previously found for domestic frying (up to 30 mg/kg after the 8^th successive frying session in sunflower oil), the probability of consuming a level of 2,4‐decadienal in restaurant‐prepared food that is higher than the level in home‐fried food was determined to be approximately one third.     

Improving the Frying Performance and Oxidative Stability of Refined Soybean Oil by Tocotrienol‐Rich Unsaponifiable Matters of Kolkhoung (Pistacia khinjuk) Hull Oil

Increasing consumer awareness for all natural products has quickly led to growing research on new resources of potent and profitable natural antioxidants. In this context, for the first time, the Kolkhoung hull oil (KHO) (Pistacia khinjuk)‐unsaponifiable matters (USM) (UHO) (100, 200, and 400 mg kg^?1) were incorporated into refined soybean oil (RSO) and the oxidative stability of prepared oils was measured during 32 hours of frying. Then, the obtained results (oxidative stability) were compared to the samples containing tert‐butyl hydroquinone (TBHQ) (100 mg kg^?1) as a common synthetic antioxidant. According to the results of oxidative stability assays of acid values, conjugated diene values and carbonyl values, and total polar compounds, the incorporation of UHO, particularly at a concentration of 200 mg kg^?1, was more efficient in improving the oxidative stability compared to TBHQ. The tocol content of KHO (2043.4 mg kg^?1) was higher than the reported amounts of other conventional edible oils. Furthermore, by incorporation of UHO into RSO, as compared with TBHQ, a better protection of naturally occurring antioxidants (tocopherols and sterols) was found after adding UHO to RSO. This fact was mainly attributed to the UHO's tocotrienol fraction. Hence, the USM of KHO can be used as a potent antioxidant to improve the oxidative stability of frying oils.     

Accumulation of 2-tert-Butyl-1,4-Benzoquinone in Frying Oil and Fried Food during Repeated Deep Fat Frying Processes

2-tert-Butyl-1,4-benzoquinone (TBBQ), the main oxidation product of tert-butyl-hydroquinone (TBHQ) during frying, is cytotoxic and its residual levels in frying oils and foods are unknown. In this study, TBBQ residues have been evaluated during the preparation of french fries. Results showed that frying at 140 °C resulted in the highest TBBQ peak concentration (48.42 mg kg⁻¹) compared with frying at 190 or 170 °C. This unexpected finding can be attributed to more extensive hydrolytic reaction when frying at the lower temperature, generating more peroxyl radicals. TBBQ concentrations proved to be independent of the oil type among various unsaturated oils. However, higher TBBQ levels were observed in saturated palm oil and crude soybean oil than in unsaturated oil or refined oil. Continuous frying leads to the accumulation of a large amount of TBBQ in fried food. After frying 1–5 batches, TBBQ levels in both the frying oil and fries were above 10 mg kg⁻¹, exceeding its critical cytotoxic concentration (IC₅₀ value of 10.71 mg kg⁻¹ for RAW 246.7 cells in our previous study), warranting concern with respect to the safety of fried food. FTIR has been utilized as an effective tool for visually monitoring the degree of oxidation in the frying medium with respect to its hydrogen peroxide level, which contributes to the increased level of TBBQ derived from TBHQ therein.     

Formation of Alkylbenzenes and Tocochromanols Degradation in Sunflower Oil and in Fried Potatoes during Deep‐Frying and Pan‐Frying

Formation of toxic alkylbenzenes, total polar compounds (%TPC) and degradation of tocochromanol are monitored. Analyses of the oil extracted from fried potatoes confirm the trend observed in the frying oil. The fresh oil has a TPC content of 3%, which increases with the frying time, exceeding the acceptable value (25%) after about 25 h for deep‐frying and 1.5 h for pan‐frying. During deep‐frying, total tocochromanol decreases to about half (25 mg per 100 g) of the initial value, pan‐frying shows faster, degradation (complete after 1.5 h). Toluene concentration increases with the frying time reaching a maximum, and afterwards gradually decreases. Except for butylbenzene during pan‐frying, pentylbenzene and butylbenzene concentration, increase with the frying time, but remain much lower than toluene. Practical Applications: This is the first systematic work comparing alkylbenzenes evolution under different frying conditions. Different from previous works, frying experiments are carried out following the indication of many European countries that recommend using temperature lower than 180 °C. The amount of alkylbenzenes assumed through a standard portion of fried potatoes (200 g) is assessed, which is relevant for evaluating dietary exposure to these contaminants.     

Comprehensive Identification of Principal Lipid Classes and Tocochromanols in Silkworm (Antheraea pernyi and Bombyx mori) Pupae Oils

A comprehensive identification of lipid compositions and tocochromanols in Antheraea pernyi (A. pernyi) and Bombyx mori (B. mori) pupae oil is reported in the present study. Fatty acid profiling shows that both oils contain high levels (79.67% vs 71.11%) of unsaturated fatty acids, especially linoleic acid and linolenic acid. Moreover, linolenic acid is preferentially enriched at the sn‐2 positions of triacylglycerols (TAGs). Liquid chromatograph‐mass spectrometry (LC‐MS) analysis demonstrates that POO (TAG with one palmitoyl and two oleoyls) is the primary TAG form with percentages of 20.18% in A. pernyi and 15.00% in B. mori. The dominating phospholipid species are phosphatidylcholine (PC, 30.40% vs 54.61%) and phosphatidylethanolamine (PE, 34.82% vs 20.39%). Four sterol constituents with total contents of 382.56 ± 3.12 and 371.65 ± 2.98 µg g^?1 are identified and analyzed quantitatively. Additionally, the levels of tocochromanols (20.15 ± 0.89 vs 17.15 ± 0.71 mg g^?1) are quantified in both silkworm pupae oils. Overall, silkworm oil acts as an enriched source of functional lipids and tocochromanols. Practical Applications: A systematic investigation on the principal lipid classes and tocochromanols of Antheraea pernyi pupae and Bombyx mori pupae oil is reported in this study. The informative data provide supporting evidence for comprehensive utilization of silkworm oil for production of nutritional and healthy products.     

Effect of Different Frying Methods on the Total <Emphasis Type="Italic">trans</Emphasis> Fatty Acid Content and Oxidative Stability of Oils

The main objective of this study was to determine the effect of different frying oils and frying methods on the formation of trans fatty acids and the oxidative stability of oils. Sunflower, canola and commercial frying oils, the most commonly used oils for frying potatoes in the fast food industry, were used as the frying medium. The value for total polar compounds was highest when commercial frying oil was used in the microwave oven (22.5 ± 1.1). The peroxide value, as an indicator of oil oxidation, was lowest for microwave oven frying (2.53 ± 0.03). The K₂₃₂ and K₂₇₀ values were 0.41 ± 0.04 and 0.18 ± 0.02, respectively, for commercial frying oil in the microwave oven. The lowest free fatty acid content was recorded for the commercial frying oil used in the deep‐fat fryer at 190 °C. The highest iodine value was measured for sunflower oil used in the deep‐fat fryer (148.14 ± 0.07), indicating a greater degree of unsaturation. The lowest trans fatty acid value was recorded for sunflower oil in the microwave oven (0.17 ± 0.05), with a higher overall amount of total trans fatty acids observed for oils after frying in the electrical deep‐fat fryer compared to the microwave. Sunflower oil was favourable for both frying methods in terms of the trans fatty acid content.     

Content of trans,trans‐2,4‐decadienal in deep‐fried and pan‐fried potatoes

Trans,trans‐2,4‐decadienal is a by‐product of frying oil that is also transferred to fried food. This aldehyde has been found and quantified both in frying oils and fumes generated during frying. Furthermore, it has been reported that 2,4‐decadienal has cytotoxic and genotoxic effects and promotes LDL oxidation. In the present work trans,trans‐2,4‐decadienal was detected directly in fried potatoes (french‐fries). Moreover, the influence of frying conditions (deep‐frying, pan‐frying), the oil type (olive oil, sunflower oil, cottonseed oil, palm oil and a vegetable shortening) and the degree of thermal deterioration (eight successive frying sessions without replenishment) on the production of 2,4‐decadienal in oil and potatoes was studied. The isolation of the aldehyde was performed by methanol extraction, while the identification and quantification was performed by RP‐HPLC. The quantity of trans,trans‐2,4‐decadienal produced during successive pan‐frying demonstrated a peak at the third and fourth frying session. The highest concentration of trans,trans‐2,4‐decadienal was detected in potatoes fried in sunflower oil, and the lowest in olive oil. The quantity of trans,trans‐2,4‐decadienal in fried potatoes decreased during successive deep‐frying at the seventh frying session or remained stable, except for cottonseed oil. The quantity of trans,trans‐2,4‐decadienal in fried potatoes was considered to be dependent on the oil used, on the frying process and, to a lesser extent, on the oil deterioration. In all cases tested, the highest concentration of trans,trans‐2,4‐decadienal was detected during deep‐frying. The unsaturation degree of the frying oil was considered to promote the formation of trans,trans‐2,4‐decadienal. Considering the quantity of 2,4‐decadienal found in french‐fries and in the respective frying medium, direct quantification of 2,4‐decadienal is required in order to make an estimation of intake from french‐fries.     

Frying quality and oxidative stability of high-oleic corn oils

To determine the frying stability of corn oils that are genetically modified to contain 65% oleic acid, high-oleic corn oil was evaluated in room odor tests and by total polar compound analysis. Flavor characteristics of french-fried potatoes, prepared in the oil, were also evaluated by trained analytical sensory panelists. In comparison to normal corn oil, hydrogenated corn oil and high-oleic (80 and 90%) sunflower oils, high-oleic corn oil had significantly (P<0.05) lower total polar compound levels after 20 h of oil heating and frying at 190°C than the other oils. Fried-food flavor intensity was significantly higher in the normal corn oil during the early portion of the frying schedule than in any of the high-oleic or hydrogenated oils; however, after 17.5 h of frying, the potatoes fried in normal corn oil had the lowest intensity of fried-food flavor. Corn oil also had the highest intensities of off-odors, including acrid and burnt, in room odor tests. High-oleic corn oil also was evaluated as a salad oil for flavor characteristics and oxidative stability. Results showed that dry-milled high-oleic corn oil had good initial flavor quality and was significantly (P<0.05) more stable than dry-milled normal corn oil after oven storage tests at 60°C, as evaluated by flavor scores and peroxide values. Although the high-oleic corn oil had significantly (P<0.05) better flavor and oxidative stability than corn oil after aging at 60°C, even more pronounced effects were found in high-temperature frying tests, suggesting the advantages of high-oleic corn oil compared to normal or hydrogenated corn oils.     

Effects of expeller-pressed/physically refined soybean oil on frying oil stability and flavor of french-fried potatoes

To determine effects of expeller pressing/physical refining of soybean oil (SBO) on frying, studies were conducted with expeller-pressed, physically refined, bleached, deodorized SBO (EPSBO); hexane-extracted, refined, bleached, deodorized SBO+TBHQ; and hydrogenated SBO (HSBO). Oils contained citric acid and dimethylpolysiloxane and were used for 35 h of frying french-fried potatoes. Polar compound levels in EPSBO were similar to SBO+TBHQ or HSBO. Flavor quality of potatoes was evaluated by trained, experienced, analytical sensory panelists. In early frying stages, potatoes fried in EPSBO had significantly lower intensities of fishiness than potatoes fried in SBO+TBHQ. Potatoes fried in HSBO were described as “hydrogenated”. Because of differences in flavor intensities and types, potatoes prepared in EPSBO had significantly better quality scores than those fried in SBO+TBHQ or HSBO during the first 15 h of frying. During later stages (25 and 35 h), potatoes fried in EPSBO had significantly better quality scores than potatoes fried in HSBO. Variations in minor oil constituents may partly explain these differences. EPSBO had less total tocopherols and phytosterols than did SBO at 0-time. During frying, TBHQ in SBO and Maillard reaction products in EPSBO probably inhibited tocopherol loss and therefore improved quality.     

A new spectrophotometric method for the rapid assessment of deep frying oil quality

A new and quick spectrophotometric method was developed to assess deep-frying oil quality. The scanned spectrophotometric curves of the frying oil samples from 350 and 650 nm wavelength changed systematically with the duration of deep frying. The absorbances of the frying oil samples, especially those measured at 490 nm, increased significantly during frying and were significantly correlated to frying time (r ≥0.95, P<0.001). There was a strong correlation between the absorbances of a set of oil samples taken from 0 to 80 h of deep frying and total polar compound contents in the same set of oil samples analyzed using the American Oil Chemists' Society official method (r=0.974, P<0.001). The equation for conversion of the absorbances to total polar compound contents is y=−2.7865x ² +23.782x+1.0309. The absorbances of 10 different types of frying oils with samples taken from 0 to 80 h of deep frying in duplicate were also strongly correlated to total polar compounds in the same oil samples (r=0.953, P<0.001, n=220). The results show that this method is fast, simple, convenient, and reliable.     

Free Fatty Acids Reduction in Waste Cooking Oil by Rhodosporidium toruloides and Simultaneous Carotenoids,Lipids, and PAL Enzyme Production in a Two-Phase Culture System

Waste cooking oil (WCO) is a problematic waste product that contains free fatty acids (FFAs), preventing it from being valorized easily as biodiesel and poses an environmental hazard if incorrectly disposed. The use of WCO as a carbon source for Rhodosporidium toruloides (R. toruloides) using a two-phase culture system is developed. The normal growth of R. toruloides when cultured in WCO (OD₆₀₀ 52) reveals its ability to use a hydrophobic substrate as the carbon source compared to glucose (OD₆₀₀ 51.9). Interestingly, the extracellular lipase activity when R. toruloides is grown on WCO is 14.4 U mL⁻¹ compared to when grown on glucose (2.4 U mL⁻¹). Additionally, FFA levels in WCO are reduced from 2% to 0.2% at end of fermentation, suggesting that R. toruloides can consume FFA. Furthermore, higher yield of beneficial products: β-carotene (4.57 µg mL⁻¹), torularhodin (4.2 µg mL⁻¹), fatty acids (1 mg mL⁻¹), and phenylalanine ammonia-lyase (PAL) enzyme (0.12 µmol mg⁻¹) are produced when WCO is the carbon source, compared to glucose (4.1 µg mL⁻¹ β-carotene, 3.0 µg mL⁻¹ torularhodin, 1 mg mL⁻¹ of fatty acids, and 0.096 µmol mg⁻¹ PAL enzyme). This is a first study that shows R. toruloides can grow on hydrophobic carbon source.     

Effects of repeated frying on physicochemical characteristics,oxidative stress,and free radical scavenging potential of canola oil and ghee

The repeated use of cooking oils and ghee for the deep frying of food materials may affect their nutritional quality. The present study evaluated the effect of repeated frying on the physicochemical characteristics and antiradical potential of canola oil and ghee. The oil and ghee were used for frying of fish and chicken for 2, 4, 6, 8, and 10 frying cycles followed by the analysis of physicochemical, oxidative stress, and antiradical parameters. Regression analysis of the data showed a frying cycle-dependent significant linear increase in saponification (R² = 0.9507–0.9748), peroxide and acid values (R² = 0.956–0.9915), and malondialdehyde (MDA) production (R² = 0.9058–0.9557) of canola oil and ghee subjected to fish and chicken frying but exponential increase in saponification value (R² = 0.9778) and MDA production (R² = 0.7407) of canola oil and ghee used for fish frying. The increase in the number of frying cycles linearly decreased the iodine value (R² = 0.9781–0.9924), and 1, 1-diphenyl-2-picrylhydrazyl, hydroxyl, and 2, 2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical scavenging potential (R² = 0.9089–0.9979) of canola oil and ghee. Repeated frying in cooking oil and ghee increases oxidative stress and decreases their physicochemical and antioxidant qualities. Canola oil was comparatively more oxidative resistant than canola ghee. The regression equations derived from regression analysis will guide researchers to conduct similar types of univariate studies.     

The Impact of Fat Deterioration on Formation of Acrylamide in Fried Foods

The current study investigates to what extent the reaction products of thermal degradation directly influence acrylamide formation in French fries. The frying tests at 170 and 180 °C are carried out with rapeseed oil for 32 h with 128 frying cycles. Acrylamide content in French fries is determined by LC-MS/MS. Oxidative and thermal degradation is followed by measuring total polar compounds (TPC), di- and polymerized triacylglycerols (DPTG), monomer oxidized triacylglycerols (MONOX), p-anisidine value (AnV), mono and di-acyl-glycerols (MAG and DAG), acid value (AV), epoxy fatty acids, iodine value (IV), saponification value, and fatty acid composition. During frying, the nature and degradation level of the frying medium have a direct impact on acrylamide formation. It can be shown that the pH-dependent reaction is strongly inhibited at acid values above 0.5 mg KOH g⁻¹ oil. Acidity measured as AV or FFA is mainly caused by oxidation, and less so by hydrolysis of triacylglycerols (TAG) as assumed up to now. Obviously, acid functional groups formed by oxidation of unsaturated fatty acids bound in TAG can act not only as catalyst for dimerization of TAG but also interact with asparagine as most important precursor for acrylamide formation so that no reaction with carbonyl groups for the formation of acrylamide is necessary. Practical applications: The same acidic functional groups that are known to catalyze the formation of dimeric TAG under frying conditions (160–190 °C, access of oxygen) in a nonradical mechanism apparently can also deactivate asparagine by protonization as a potential precursor for the formation of acrylamide. It is recommended not to reduce acidity of used frying oil by active filter aids below AV ≥ 0.5 as it helps to reduce acrylamide contamination of fried food.     

Hydroperoxide as a Prooxidant in the Oxidative Stability of Soybean Oil

Fifteen milliliters of soybean oil having peroxide value (PV) of 0, 2, 4, 6, 8, or 10 meq/kg oil in a 35 mL serum bottle was sealed air-tight with a Teflon rubber septum and aluminum cap and was stored in a forced-air oven at 50 °C. The oxidative stability of soybean oil was evaluated daily for six days by measuring the headspace oxygen content and volatile compounds in the headspace of a sample bottle by gas chromatography. As the initial PV of the oil increased from 0 to 2, 4, 6, 8 and 10, the headspace oxygen decreased and the volatile compounds increased at p < 0.05. Hydroperoxide accelerated the oxidation of soybean oil. The correlation coefficient (R ²) between the headspace oxygen and the volatile compounds was 0.95. The increase of tertiary butyl hydroquinone (TBHQ) from 0 to 50 ppm for the oil of PV 4 or 8 had a significant effect on the oxidative stability at p < 0.05. The increase from 50 to 100 ppm for the oil of PV 4 or 8 did not significantly increase the stability at p > 0.05. The oxidative stability of PV 8 meq/kg and 50 ppm TBHQ was better than the control with PV 0 and 0 ppm TBHQ at p < 0.05. TBHQ was an effective antioxidant to improve the oxidative stability of soybean oil.     

Frying stability of soybean and canola oils with modified fatty acid compositions

Pilot plant-processed samples of soybean and canola (lowerucic acid rapeseed) oil with fatty acid compositions modified by mutation breeding and/or hydrogenation were evaluated for frying stability. Linolenic acid contents were 6.2% for standard soybean oil, 3.7% for low-linolenic soybean oil and 0.4% for the hydrogenated low-linolenic soybean oil. The linolenic acid contents were 10.1% for standard canola oil, 1.7% for canola modified by breeding and 0.8% and 0.6% for oils modified by breeding and hydrogenation. All modified oils had significantly (P<0.05) less room odor intensity after initial heating tests at 190°C than the standard oils, as judged by a sensory panel. Panelists also judged standard oils to have significantly higher intensities for fishy, burnt, rubbery, smoky and acrid odors than the modified oils. Free fatty acids, polar compounds and foam heights during frying were significantly (P<0.05) less in the low-linolenic soy and canola oils than the corresponding unmodified oils after 5 h of frying. The flavor quality of french-fried potatoes was significantly (P<0.05) better for potatoes fried in modified oils than those fried in standard oils. The potatoes fried in standard canola oil were described by the sensory panel as fishy.     

Effect of the Presence and Absence of Potatoes under Repeated Frying Conditions on the Composition of Palm Oil

The effect of repeated deep frying of potatoes versus repeated heating/quenching on the chemical profile of palm oil was investigated. The novelty of the work is that the frying and heating/quenching experiments were conducted under similar time-temperature profiles. The effects of the frying load (potato-to-oil ratio: 1/7 and 1/35 kg_potatoes/l_oil) and of the time-temperature profile were examined. Whole palm oil and its polar fraction were analyzed using high pressure size exclusion chromatography. Both repeated frying and repeated heating/quenching generated polar and polymerization products in palm oil. Interestingly, no hydrolysis or other decomposition products were generated under any of the examined conditions. The presence of potatoes during frying in palm oil increased the concentration of polymerization products and polar compounds compared to oils without potatoes significantly. The effects of frying load on oil quality depended on frying time. No significant effect of frying load was observed up to frying times of 13 h (or 10 frying batches). However, frying oil quality was affected by frying load once frying times exceeded 24 h (or 20 batches).     

Changes in Total Polar Compounds,Peroxide Value,Total Phenols and Antioxidant Activity of Various Oils Used in Deep Fat Frying

In this study, the effect of deep fat frying on oil degradation, total phenols (TP) and total antioxidant activity (TAA) of hazelnut, corn, soybean and olive oils were investigated. Oil degradation and oxidation were monitored by measuring the total polar compounds (TPC) and the peroxide value (PV). The amount of TPC in corn, soybean and olive oils increased significantly with the time increment (p < 0.05). The PV of the oils did not exceed the maximum acceptable limit of 10 mequiv O₂/kg after 125 min frying except for hazelnut oil (10.64 mequiv O₂/kg). Deep-fat frying did not cause any significant change in the TP of corn oil, soybean oil and olive oil (p < 0.05). A significant decrease in the antioxidant activity was observed after 50 min frying using hazelnut oil and corn oil (p < 0.05). However, the antioxidant activity of soybean oil and olive oil significantly decreased after 75 and 25 min frying, respectively.