Chemical and physical analyses and sensory evaluation of six deep-frying oils

The performance of three high-oleic canola oils with different levels of linolenic acid [low-linolenic canola (LLC), medium-linolenic canola (MLC), and high-linolenic canola (HLC)], a medium-high-oleic sunflower oil, a commercial palm olein and a commercial, partially hydrogenated canola oil, was monitored by chemical and physical analyses and sensory evaluation during two 80-h deep-frying trials with potato chips. Linolenic acid content was a critical factor in the deep-frying performance of the high-oleic canola oils and was inversely related to both the sensory ranking of the food fried in the oils and the oxidative stability of the oils (as measured by color index, free fatty acid content, and total polar compounds). LLC and sunflower oil were ranked the best of the six oils in sensory evaluation, although LLC performed significantly better than sunflower oil in color index, free fatty acid content, and total polar compounds. MLC was as good as palm olein in sensory evaluation, but was better than palm olein in oxidative stability. Partially hydrogenated canola oil received the lowest scores in sensory evaluation. High-oleic canola oil (Monola) with 2.5% linolenic acid was found to be very well suited for deep frying.     

Utilization of high‐oleic rapeseed oil for deep‐fat frying of French fries compared to other commonly used edible oils

Changes in chemical, physical and sensory parameters of high‐oleic rapeseed oil (HORO) (NATREON?) during 72 h of deep‐fat frying of potatoes were compared with those of commonly used frying oils, palm olein (PO), high‐oleic sunflower oil (HOSO) and partially hydrogenated rapeseed oil (PHRO). In addition to the sensory evaluation of the oils and the potatoes, the content of polar compounds, oligomer triacylglycerols and free fatty acids, the oxidative stability by Rancimat, the smoke point and the anisidine value were determined. French fries obtained with HORO, PO and HOSO were still suitable for human consumption after 66 h of deep‐fat frying, while French fries fried in PHRO were inedible after 30 h. During the frying period, none of the oils exceeded the limit for the amount of polar compounds, oligomer triacylglycerols and free fatty acids recommended by the German Society of Fat Science (DGF) as criteria for rejection of used frying oils. After 72 h, the smoke point of all oils was below 150 °C, and the amount of tocopherols was reduced to 5 mg/100 g for PHRO and 15 mg/100 g for HORO and HOSO. Remarkable was the decrease of the oxidative stability of HOSO measured by Rancimat. During frying, the oxidative stability of this oil was reduced from 32 h for the fresh oil to below 1 h after 72 h of frying. Only HORO showed still an oxidative stability of more than 2 h. From the results, it can be concluded that the use of HORO for deep‐fat frying is comparable to other commonly used oils.     

The Effect of Type of Oil and Degree of Degradation on Glycidyl Esters Content During the Frying of French Fries

The aim of the study was to determine the effect of oil degradation on the content of glycidyl esters (GEs) in oils used for the frying of French fries. As frying media, refined oils such as rapeseed, palm, palm olein and blend were used. French fries were fried for 40 h in oils heated to 180 °C in 30‐min cycles. After every 8 h of frying, fresh oil and samples were analyzed for acid and anisidine values, color, refractive index, fatty acid composition, and content and composition of the polar fraction. GEs were determined by LC–MS. Hydrolysis and polymerization occurred most intensively in palm olein, while oxidation was reported for rapeseed oil. The degradation of oil caused increased changes in the RI of frying oils. Losses of mono‐ and polyunsaturated fatty acids were observed in all samples, with the largest share in blend. The highest content of GE found in fresh oil was in palm olein (25 mg kg^?1) and the lowest content of GE was found in rapeseed oil (0.8 mg kg^?1). The palm oil, palm olein and blend were dominated by GEs of palmitic and oleic acids, while rapeseed oil was dominated by GE of oleic acid. With increasing frying time, the content of GEs decreased with losses from 47 % in rapeseed oil to 78 % in palm oil after finishing frying.     

Storage stability of potato chips fried in genetically modified canola oils

The storage stability of potato chips fried in regular (RCO), hydrogenated (HYCO), low-linolenic (LLCO), and high-oleic (HOCO) canola oils was compared. Potato chips were fried in each oil over a 5-d period for a total of 40 h of frying. Chips from frying day 1 and 5 were packaged and stored at 60°C for 0, 1, 2, 4, 8, and 16 d. Lipids were extracted from the stored chips and analyzed for peroxide values, free fatty acids (FFA), conjugated dienoic acids (CDA), and polar components. A trained sensory panel evaluated the stored chips for odors characteristic of oxidation. Chips were also analyzed for volatile components. Potato chips fried in RCO, LLCO and HOCO developed an intense painty odor, whereas chips fried in HYCO developed an intense stale/musty odor by the end of the 16 d of storage. Chips fried in RCO had greater rates of accumulation of peroxides, FFA, CDA, and polar components and developed higher levels of total volatiles over the 16 d of storage than chips fried in the other three oils. Chips fried in HYCO had lower rates of accumulation of peroxides and CDA than chips fried in LLCO and HOCO, and lower rates of FFA accumulation than chips fried in LLCO. Chips fried in HYCO and HOCO had the lowest amounts of total volatiles during storage. The effect of oil degradation products on potato chip storage stability was not shown in this study since only the chips fried in HYCO from frying day 5 exhibited a significantly greater rate of off-odor development than chips from frying day 1, and only the chips fried in LLCO from frying day 5 had a greater rate of accumulation of volatiles than chips from frying day 1.     

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.     

Studies on phytosterol oxides. II: Content in some vegetable oils and in French fries prepared in these oils

Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations. After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4 to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol are reported for the first time. Part of these results were presented at the 86th Annual Meeting of the AOCS, May 7–11, 1995, San Antonio, TX.     

Review of stability measurements for frying oils and fried food flavor

Measurements of degradation in frying oils based on oil physical properties and volatile and nonvolatile decomposition products were reviewed. Rapid methods by means of test kits were also considered. Factors that affect the analysis of total polar components (TPC) in frying oils were examined. Relationships between TPC, free fatty acid (FFA) content, Food Oil Sensor readings (FOS), color change (ΔE), oil fry life and fried-food flavor were evaluated. Flavor scores for codfish, fried in fresh and discarded commercial frying oil blends, were dependent upon individuals in the consumer panel (n=77). Part (n=29) of the panel preferred the flavor of fresh fat; others (n=24) didn't; the rest (n=24) had no preference. FFA, FOS and TPC were analyzed in two soybean oils and in palm olein during a four-day period in which french fries were fried. Flavor score and volatiles of potatoes fried on days 1 and 4 in each oil were also determined. TPC, FFA and FOS significantly increased (P<0.05) in all oils during the frying period. TPC and FFA were highest in the used palm olein, and flavor of potatoes fried in palm olein on day 1 was less desirable than those fried in the soybean oils. Potatoes fried in day-1 oils had significantly higher concentrations (P<0.10) of several pyrazines and aldehydes than those fried in day-4 oils. Presented at the 84th Annual Meeting of the American Oil Chemists' Society, Anaheim, California, April 25–29, 1993.     

Performance of Regular and Modified Canola and Soybean Oils in Rotational Frying

Canola and soybean oils both regular and with modified fatty acid compositions by genetic modifications and hydrogenation were compared for frying performance. The frying was conducted at 185 ± 5 °C for up to 12 days where French fries, battered chicken and fish sticks were fried in succession. Modified canola oils, with reduced levels of linolenic acid, accumulated significantly lower amounts of polar components compared to the other tested oils. Canola oils generally displayed lower amounts of oligomers in their polar fraction. Higher rates of free fatty acids formation were observed for the hydrogenated oils compared to the other oils, with canola frying shortening showing the highest amount at the end of the frying period. The half-life of tocopherols for both regular and modified soybean oils was 1–2 days compared to 6 days observed for high-oleic low-linolenic canola oil. The highest anisidine values were observed for soybean oil with the maximum reached on the 10th day of frying. Canola and soybean frying shortenings exhibited a faster rate of color formation at any of the frying times. The high-oleic low-linolenic canola oil exhibited the greatest frying stability as assessed by polar components, oligomers and non-volatile carbonyl components formation. Moreover, food fried in the high-oleic low-linolenic canola oil obtained the best scores in the sensory acceptance assessment.     

Choice of Simple Methods for Quality Control of Frying Fat during Deep Frying of Potato Products

Studies have been carried out to choice methods which could assess in best way the complex changes in fat during deep frying of French fries and potato crisps. A special emphasis was laid on the estimation of usefulness of simple and quick “methods” which could practically indicate the utilization time of fats (soybean oil, low erucic acid rapeseed oil, ?Sofryt”? -hardened soybean oil), used in deep-fat frying of potato products. Besides the oxidized fatty acid content, proposed by DGF (German Society for Fat Science) as a basic test for the quality assessment of used frying fats, following control tests during the deep-fat frying of potato products have been appointed: colour tests with bromthymol blue and 2,6-dichlorphenol-indophenol, sensoric evaluation, dielectric constant and colour by iodine scale. For these tests suitable limits, qualifying the utility of oils and fats for further frying of French fries and potato crisps, have been estimated.     

Influence of Prolonged Deep-Frying Using Various Oils on Volatile Compounds Formation of French Fries Using GC–MS,GC-O,and Sensory Evaluation

Flavor is a decisive sensory characteristic to determine the popularity of French fries (FF). To investigate the effect of prolonged deep-frying using various oils on volatiles formation of FF, the FF were prepared in the palm oil (PO), soybean oil (SO), and high-oleic rapeseed oil (RO) for 24 hours intermittent frying. The effect of oil types was found to be more significant than the frying time on the volatiles of FF indicated from the clusters of the fried FF by chemometric analysis. A total of 26 key aroma-active compounds were identified by aroma extract dilution analysis, in which aldehydes were predominant. The FF fried in SO revealed higher desirable aroma compounds, i.e., (E, E)-2,4-decadienal and it increased to maximum value at 12 hours, and left the deep-fried odor in FF. Meanwhile, a significant increase in metallic off-flavor was observed in FF fried in SO and PO at 20 hours, indicating that oil quality reduction resulted in FF with unappealing flavor. The above results showed that frying process had an optimum frying window (approximately 4–16 hours with total polar compounds content below 22.2%), and the French fries prepared in this period obtained higher flavor scores. The study will provide insights into the effect of oil types and oxidation degree on obtaining the ideal flavors for fried food.     

Effects of natural and synthetic antioxidants on changes in refined, bleached, and deodorized palm olein during deep-fat frying of potato chips

The effects of antioxidants on the changes in quality characteristics of refined, bleached, and deodorized (RBD) palm olein during deep-fat frying (at 180°C) of potato chips for 3.5 h/d for seven consecutive days in five systems were compared in this study. The systems were RBD palm olein without antioxidant (control), with 200 ppm butylated hydroxytoluene (BHT), 200 ppm butylated hydroxyanisole (BHA), 200 ppm oleoresin rosemary, and 200 ppm sage extract. Fried oil samples were analyzed for peroxide value (PV), thiobarbituric acid (TBA) value, iodine value (IV), free fatty acid (FFA) content, polymer content, viscosity, E^1% _{1 cm} at 232 and 268 nm, color, fatty acid composition, and C_18:2/C_16:0 ratio. Sensory quality of the potato chips fried in these systems prior to storage was also evaluated. The storage stability of fried potato chips for 14 wk at ambient temperature was also determined by means of the TBA values and sensory evaluation for rancid odor. Generally, in the oil, oleoresin rosemary gave the lowest rate of increase of TBA value, polymer content, viscosity, E^1% _{1 cm} at 232 and 268 nm compared to control and three other antioxidants. The order of effectiveness (P<0.05) in inhibiting oil oxidation in RBD palm olein was oleoresin rosemary > BHA > sage extract > BHT > control. Prior to storage, the sensory evaluation of fried potato chips for each system showed that there was no significant (P>0.05) difference in terms of flavor, odor, texture, and overall acceptability. The same order of effectiveness (P<0.05) of antioxidants was observed for storage stability study of fried potato chips by TBA values. However, there was no significant (P > 0.05) difference in sensory evaluation for rancid odor during storage periods.     

Studies on Quality of Coconut Oil Blends after Frying Potato Chips

The quality (chemical and sensory) of oil blends prepared by blending equal proportions of coconut oil with sesame oil (blend 1), coconut olein with sesame oil (blend 2) and coconut olein with palmolein (blend 3) was evaluated after deep-fat frying of potato chips. After frying, the free fatty acid content did not change, however, the anisidine value increased. Blend 2 had the highest anisidine value (44.0). A marginal decrease in the iodine value and an increase in the diene values were observed in blends 1 and 2. The β-carotene content in blend 3 and tocols in all the three blends were found to decrease after frying. Sensory odor profiles of oil blends after frying showed a decrease in the characteristic coconut oil aroma. The earthy and seedy aroma associated with sesame oil was found to decrease on frying. The sensory profile of potato chips showed a slight bitter taste in the samples fried in blends 1 and 2. However, the intensity of bitterness decreased and the earthy note increased on storage. Blend 3 had the highest overall quality.     

Frying Quality Characteristics of French Fries Prepared in Refined Olive Oil and Palm Olein

The objective of this study was to compare two oils with different polyunsaturated/saturated (P/S) fatty acid ratios, refined olive oil (P/S 0.75) and palm olein (P/S 0.25), in frying French fries. The chemical qualities of the oil residues extracted from the French fries were assayed for five consecutive batches fried at 1-h intervals. The levels of total polar compounds, free fatty acids, p-anisidine value and phytosterol oxidation products (POPs) were elevated in French fries fried in both oils. The level of total polar compounds increased from 4.6 in fresh refined olive oil to 7.3% in final batches of French fries. The corresponding figures for palm olein were 9.8–13.8%. The level of free fatty acid in fresh refined olive oil increased from 0.06 to 0.11% in final products. These figures for palm olein were 0.04–0.13%. The p-anisidine value increased from 3.7 to 32.8 and 2.5 to 53.4 in fresh oils and in final batches of French fries in refined olive oil and palm olein, respectively. The total amount of POPs in fresh refined olive oil increased from 5.1 to 9.6 μg/g oil in final products. These figures were 1.9 to 5.3 μg/g oil for palm olein.     

Effects of hydrogenation and additives on cooking oil performance of soybean oil

Soybean oil was continuously hydrogenated in a slurry system to investigate the effects of linolenate content and additives on cooking oil performance. Room odor evaluations carried out on oils heated to 190 C after frying bread cubes showed that the oils hydrogenated with Cu catalyst to 2.4% linolenate (Cu-2.4) and with Ni catalyst to 4.6 linolenate (Ni-4.6) had a significantly lower odor intensity score than the unhydrogenated soybean oil (SBO). Other hydrogenated oils (Cu-0.5 and Ni-2.7) were not significantly better than SBO. Oil hydrogenated with Ni (Ni-0.4) scored poorly because of its strong “hydrogenated-paraffin” odor. The performance of all partially hydrogenated oils (2.4, 2.7 and 4.6% linolenate) was improved by adding methyl silicone (MS), but the most hydrogenated oils (0.5 and 0.4% linolenate) were not improved. Although with tertiary butyl hydroquinone (TBHQ) no improvement was obtained, with the combination of TBHQ + MS all odor scores were lower, indicating a synergistic effect. Evaluations of bread cubes after intermittent heating and frying showed that the breads fried in most hydrogenated oils (Ni-0.4, Cu-2.4 and Ni-2.7) were rated significantly better in flavor quality than breads fried in SBO. The bread cubes fried in MS-treated oils had significantly higher flavor quality scores than breads fried in SBO or SBO containing TBHQ. Dimer analyses by gel permeation chromatography and color development after heat treatments also did not correlate with sensory analyses.     

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 antioxidants on refined palm oil

Alkali refined palm oil and hydrogenated cotton-seed oil were stabilized with butylated hydroxytoluene, butylated hydroxyanisole, and tertiary butylhydroquinone. Under bulk storage temperatures significant reductions in the peroxide formation of palm oil were obtained only with tertiary butyl-hydroquinone. The reduction in peroxide formation with tertiary butylhydroquinone was much greater than anticipated from the active oxygen method results. The stability improvement of a snack product fried in palm oil stabilized with tertiary butylhydroquinone depended greatly on the frying conditions used. Under mild frying conditions tertiary butyl-hydroquinone had somewhat greater carry-through than butylated hydroxytoluene. Under more severe frying conditions tertiary butylhydroquinone provided less protection than butylated hydroxytoluene. Both palm oil and hydrogenated cottonseed oil stabilized with only butylated hydroanisole had higher active oxygen stabilities than the unstabilized controls; however, no reduction in peroxide formation of the butylated hydroxyanisole oils compared to the controls was found during storage of the oil or the snack product at 50–60 C.     

Effect of fatty acid composition of oils on flavor and stability of fried foods

Effects of fatty acid composition of frying oils on intensities of fried-food flavor and off-flavors in potato chips and french-fried potatoes were determined. Commercially processed cottonseed oil (CSO) and high-oleic sunflower oil (HOSUN) were blended to produce oils with 12 to 55% linoleic acid and 16 to 78% oleic acid. Analytical sensory panels evaluated french-fried potatoes and pilot plant-processed potato chips. Initially, both foods prepared in CSO (16% oleic/55% linoleic acid) had the highest intensities of fried-food flavor; however, this positive flavor decreased with decreasing levels of linoleic acid. 2,4-Decadienal in potato chips also decreased with decreasing linoleic acid in the oils. Frying oil stability, measured by total polar compounds (TPC), and oxidative stability of potato chips, measured by volatile compounds, showed that HOSUN (78% oleic acid) produced the lowest levels of TPC and the lowest levels of hexanal and pentanal, indicating greater frying oil stability and oxidative stability of the food. However, fresh potato chips fried in HOSUN had the lowest intensities of fried-food flavor and lowest overall flavor quality. Fried-food flavor intensity was the best indicator of overall flavor quality in fresh potato chips. Volatile compounds, TPC, and oxidative stability index directly varied with increasing oleic acid, and were therefore not directly indicative of flavor quality. No oil analysis predicted flavor stability of aged potato chips. Compositions of 16 to 42% oleic acid and 37 to 55% linoleic acid produced fresh fried-food with moderate fried food flavor intensity, good overall flavor quality, and low to moderate TPC levels (chips only). However, in aged food or food fried in deteriorated oil, compositions of 42 to 63% oleic and 23 to 37% linoleic provided the best flavor stability.     

Suitability of hydrogenated soybean oils for prefrying of deep-frozen french fries

The suitability of hydrogenated soybean oils (fats) for prefrying of deep-frozen french fries has been investigated in a frying and storage experiment with five hydrogenated oils, of which four were commercially available and one was experimentally prepared. Three frying oils were hydrogenated soybean fats (0% C18:2 and C18:3), one was a partly hydrogenated soybean oil (25% C18:2; 0% C18:3) and one a hydrogenated palm fat (0% C18:2). An intermittent frying and heating procedure was used. Prefried french fries were stored deep-frozen at ?18 to ?20 C for a period of one year. Although differences in hydrolysis and oxidation during frying were observed, the five hydrogenated frying oils were quite stable. During the storage period, hydrolytic and oxidative changes in the oil phase of prefried french fries were not detected, regardless of the frying oil used. Only slight changes in sensory quality could be detected in all french fry samples stored for one year at ?18 to ?20 C. Some differences in odor and taste of finish-fried french fries observed initially were not observed after prolonged storage. Thus, it has been concluded that hydrogenated soybean oils, including a partly hydrogenated one, are suitable for prefrying french fries and for long-term storage of deep-frozen products.     

Effects of α-Tocopherol on Oxidative Stability and Phytosterol Oxidation During Heating in Some Regular and High-Oleic Vegetable Oils

The first part of this study evaluated oxidative stability in high-oleic rapeseed oil, palm olein, refined olive oil, low erucic acid rapeseed oil and sunflower oil. The results showed oxidative stability in the order: palm olein > high-oleic rapeseed oil > refined olive oil > low erucic acid rapeseed oil > sunflower oil, as determined by the Rancimat method. Addition of α-tocopherol at high levels of up to 0.2% increased the oxidative stability of refined olive oil, whereas the opposite effect was generally observed in the other oil samples. In the second part of the study, high-oleic rapeseed oil, palm olein, refined olive oil and refined olive oil containing 0.2% α-tocopherol were heated for 3, 6, 9 and 12 h at 180 °C. The peroxide and p-anisidine values generally increased over time in the samples, including olive oil containing 0.2% α-tocopherol. High-oleic rapeseed oil contained the highest amount of total sterols and total phytosterol oxidation products (POPs), but during heating the total POPs content increased moderately (~10%), in contrast to the threefold increase after 12 h of heating in palm olein and refined olive oil. Very high levels of 6-hydroxy derivatives of brassicastanol, campestanol and sitostanol and of 7-ketobrassicasterol were observed in high-oleic rapeseed oil samples. Addition of 0.2% α-tocopherol during heating significantly decreased POPs formation in refined olive oil (P < 0.05).     

Odor Significance of the Volatiles Formed During Deep-Frying With Palm Olein

Palm olein is currently considered to be one of the best options for deep-frying, but as with any other edible oil, during frying, deteriorative reactions produce off-flavor compounds that reduce the oil sensory quality. This study assessed the odor significance of the volatiles formed during 136 h of deep-frying a chicken product in palm olein, aiming to identify potential markers of the oil sensory quality during frying. The volatiles were isolated by solid phase microextraction, and identified by GC–MS. Trained judges assessed the odor intensity and quality of the volatiles formed during frying, evaluating the GC effluents through a GC–olfactometry technique called OSME. Two hundred and eight volatiles were detected by GC/MS in the palm olein after 136 h frying. Of these, heptanal, t-2-heptenal, decanal and t-2-undecenal were identified as potential markers of the sensory quality of palm olein during frying. Hexanal, pentanal and pentane, usually associated with lipid oxidation, showed no odor impact in the GC effluents, and were thus proven not to be good markers of the sensory quality of palm olein when used for a long frying period.