Carbon dioxide blanketing impedes the formation of 4‐hydroxynonenal and acrylamide during frying. A novel procedure for HNE quantification

Acrylamide and 4‐hydroxynonenal (HNE) are among the most detrimental compounds formed during high temperature processing of food. The effect of carbon dioxide blanketing (CDB) on the formation and accumulation in food of these compounds during deep‐fat frying was investigated. French fries were fried for 7 h daily and for 7 days in canola oil at 185 ± 5°C without and with CO₂ protection. The amount of acrylamide and HNE accumulated in the French fries were analyzed. Compared to standard frying conditions (SFC), frying under CDB reduced the amount of HNE by 62%. On the 3rd day of frying, the amount of acrylamide in fries fried under SFC was 3.3 times higher compared to frying with CO₂ protection. Frying with carbon dioxide protection is an effective and practical way to impede formation of toxic components during deep‐fat frying. To assess formation of HNE a simple, sensitive and reliable procedure for HNE analysis in frying oils and fried products was developed and evaluated. Practical applications : The toxicity of HNE and acrylamide, coupled with the increasing consumption of fried foods necessitates that measures be taken to reduce their formation and subsequent accumulation in fried foods. The frying method proposed in this study is very effective and requires only a simple modification to the fryer. Developed rapid and simple procedure for HNE analysis allows more accurate quantification.     

A Review on Frying: Procedure,Fat, Deterioration Progress and Health Hazards

For decades, frying has been a popular technique for the preparation of foods, both on domestic and industrial scales. The effects of edible oil type and frying operation conditions on the shelf‐life of fried products, the deterioration progress and the health hazards of fried foods have been studied by various researchers. To achieve a clear conception of the present situation, a collection of the results obtained from previous studies about product deterioration and safety issues due to the frying process, along with related tables, are of prime importance. According to the studies, it can be concluded that a vacuum, oil replenishment, frying temperature, and time of process are the most important parameters affecting the quality of oils and fried products; hence, by controlling them, it is possible to prevent the formation of toxic compounds and loss of nutritional components to a considerable extent during frying operation. Furthermore, according to recent studies indicating significant formation of toxic compounds before the chemical indices of the oil reach the disposal point, more studies are needed to determine whether they are formed at levels that compromise safety and affect consumers’ sensory perception before the established discard points.     

Quality of fried foods with palm oil

The amount of imported palm oil in Japan during the past few years has been 140,000–150,000 tons per year, or about 9% of the total consumption of vegetable oils in Japan. In 1975, part of the palm oil was imported as refined type from Malaysia. At the present time, almost all of the palm oil from Malaysia is refined. At the starting point quality of the refined palm oil was not so good, but today it is fairly improved by efforts of Malaysian processers. Palm oil has excellent properties against oxidation, and it has been generally accepted by consumers as a vegetable oil for health foods. There also is a big potential for increasing consumption of palm oil in fried foods. Severe regulation of food additives restricts the use of artificial antioxidants and therefore strict quality control is required to get stable frying oils. Consumer knowledge of foods is increasing, and our responsibility for making good quality frying fats is very important.     

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.     

Stability of Essential Fatty Acids and Formation of Nutritionally Undesirable Compounds in Baking and Shallow Frying

During cooking oils and fats are exposed to high temperatures that may affect the nutritional quality of foods that are prepared in this way. Concerns have been raised about the degradation of polyunsaturated fatty acids and the formation of potentially harmful compounds during deep frying, but relatively little is known about these changes in other cooking processes. In the present study sponge cakes and fried potatoes were prepared via standardised baking and shallow frying procedures by using different oils and fats (sunflower oil, rapeseed oil, various margarines or butter). The effect of cooking on the retention of two essential fatty acids (linoleic acid and α-linolenic acid) and the formation of trans fatty acids (TFA) and polymerised triacylglycerols (PTG) was evaluated by analyzing fat extracted from the cooked food. It was found that over 95 % of essential fatty acids were retained upon completion of both cooking techniques. The formation of TFA was not significant. Polymerisation was noticeable only in shallow frying, although the final levels of PTG were negligible (<1.3 %). Overall, in contrast to deep frying, oil-based media high in polyunsaturated fatty acids seem to be a good alternative for domestic cooking techniques as they increase the nutritional value of the prepared food.     

Incorporation of the toxic aldehyde 4-hydroxy-2-<Emphasis Type="Italic">trans</Emphasis>-nonenal into food fried in thermally oxidized soybean oil

The toxic aldehyde 4-hydroxy-2-trans-nonenal (HNE) is an oxidation product of linoleic acid and is formed during the thermal oxidation of soybean oil at frying temperature. This investigation was conducted to determine whether HNE would be incorporated into food fried in thermally oxidized soybean oil. Commercially available liquid soybean oil was heated at 185°C for 5 h prior to frying uniform pieces of potato (1×0.5×7 cm). The oil was sampled prior to and after frying and was analyzed for the presence of HNE and other polar lipophilic aldehydes and related carbonyl compounds by HPLC. The oil was also extracted from the fried potato pieces and was analyzed identically to the frying oil. HNE was found to be a major polar lipophilic compound in the thermally oxidized frying oil, as previously published by this laboratory, and in the oil extracted from the fried potato. Similar concentrations of HNE were found in the oil prior to and after frying and in the oil extracted from the fried potato (57.53±16.31, 52.40±6.10, and 59.64±11.91 mg HNE per 100 g oil, respectively). These results indicate that toxic HNE was readily incorporated into food fried in thermally oxidized oil; extensive consumption of such fried foods could be a health concern.     

Antioxidative properties of phenolic acids and interaction with endogenous minor components during frying

The ability of selected phenolic acids to improve the frying performance of canola oil was evaluated in a frying test. The frying performance of the oil was assessed by analysis of total polar components (TPC), level of 4‐hydroxynonenal (HNE), and the rate of formation of volatile carbonyl compounds (VCC). All the tested phenolic acids; ferulic acid (FA), caffeic acid (CA), dihydrocaffeic acid (HCA), gallic acid (GA), and vanillic acid (VA) significantly increased the frying performance of canola oil triacylglycerols (CTG). At the end of the frying test, the amount of TPC in CTG was 22.9 ± 1.0% compared to a maximum of 18.8 ± 0.8% in CTG fortified with the phenolic acids. Similarly, the level of HNE was reduced by up to 45% when it was supplemented with phenolic acids. The results showed that ethyl ferulate (EF) was a better antioxidant than FA under frying conditions; HCA offered a slightly better protection than CA; and the cinnamic acid derivative, FA was better than VA, its benzoic acid analogue. A significant synergy was observed between phenolic acids and the sterol fraction isolated from canola oil. The observed synergy was attributed to the possible formation of steryl phenolates during the frying test. Practical applications: The poor thermal stability of polyunsaturated oils limits their application for prolonged frying. PUFA offer important health benefits and can improve nutritional value of fried foods. Contrary to the commonly applied synthetic antioxidants, the phenolic acids tested in this study often are part of endogenous oil components present in oilseeds and also in some oils, and are known for their positive health benefits. Thus, the simple phenolic acids, especially the cinnamic acid derivatives may be applied as potent antioxidants to protect oils during thermal processes used for food production.     

Accumulation of 5-Hydroxymethylfurfural in Oil During Frying of Model Dough

5-Hydroxymethylfurfural (HMF), a thermal process contaminant, forms in food during frying as a result of the Maillard reaction and caramelization. Owing to its chemical properties, HMF formed in foods during frying partially transfers into frying oil. This study aimed to investigate the accumulation of HMF in oil during repetitive frying operations. A model dough composed of 25 % of glucose was fried at 160, 170, 180 °C for 50 frying cycles. Apart from total polar compounds (TPC), accumulation of HMF was determined in oils during repetitive frying operations. Increasing frying temperature also increased the amount of HMF formed in dough, and those transferred to oil. Prolonging frying cycles to 150, increasing amount of dough being fried to 100 g and frying time to 10 min caused the TPC content to reach 25 % at the 130th frying cycle at 180 °C. Under the same frying conditions, the concentration of HMF showed a rapid increase at the first 10th frying cycle. Its increase was at a slower rate until the 50th frying cycle reaching a plateau level exceeding 5.0 mg/L. The results revealed that HMF transferred and accumulated in the frying oil during repetitive frying. The HMF concentration exceeding 5.0 mg/L in oil may be considered as an indicator for heavily used frying oil. Correlation between TPC and HMF contents of frying oil showed no linear correlation.     

The Effects of Microwave Frying on Physicochemical Properties of Frying and Sunflower Oils

Deep fat frying is a method of food preparation which has been popular for quite a number of years. During deep frying, the quality of oil and the finished product decreases as the result of heat treatment of the oil exposed to air at high temperature. Application of heat by microwave as an alternative to the conventional method of frying has become popular in recent years. In this research, the effects of microwave frying on the changes in the quality indices of used oil have been investigated. To achieve this, potato slices were fried in both frying and sunflower oils by application of medium power microwave (550 W) for 20 min, three times a day, for five consecutive days, and oils were sampled for analysis. The results obtained from the chemical tests demonstrated that used frying oil had lower polar compounds, a higher induction period, and more saturated fatty acids than sunflower oil. The interesting point observed was that peroxides formed as the result of oxidation chain reactions were not broken down and were built up due to the lower temperature and shorter period of frying. Therefore microwave frying might be considered as a suitable alternative to the conventional frying due to less degradation of the oil and consequently a lower production of artifacts.     

Performance evaluation of hexane-extracted oils from genetically modified soybeans

Soybeans produced by induced mutation breeding and hybridization were cracked, flaked and hexane-extracted, and the recovered crude oils were processed to finished edible oils by laboratory simulations of commercial oil-processing procedures. Three lines yielded oils containing 1.7, 1.9 and 2.5% linolenic acid. These low-linolenic acid oils were evaluated along with oil extracted from the cultivar Hardin, grown at the same time and location, and they were processed at the same time. The oil from Hardin contained 6.5% linolenic acid. Low-linolenic acid oils showed improved flavor stability in accelerated storage tests after 8 d in the dark at 60°C and after 8h at 7500 lux at 30°C, conditions generally considered in stress testing. Room odor testing indicated that the low-linolenic oils showed significantly lower fishy odor after 1 h at 190°C and lower acrid/pungent odor after 5 h. Potatoes were fried in the oils at 190°C after 5, 10 and 15 h of use. Overall flavor quality of the potatoes fried in the low-linolenic oils was good and significantly better after all time periods than that of potatoes fried in the standard oil. No fishy flavors were perceived with potatoes fried in the low-linolenic oils. Total volatile and polar compound content of all heated oils increased with frying hours, with no significant differences observed. After 15 h of frying, the free fatty acid content in all oils remained below 0.3%. Lowering the linolenic acid content of soybean oil by breeding was particularly beneficial for improved oil quality during cooking and frying. Flavor quality of fried foods was enhanced with these low-linolenic acid oils.     

Mid-Oleic/Ultra Low Linolenic Acid Soybean Oil: A Healthful New Alternative to Hydrogenated Oil for Frying

To determine the frying stability of mid-oleic/ultra low linolenic acid soybean oil (MO/ULLSBO) and the storage stability of food fried in it, tortilla chips were fried in MO/ULLSBO, soybean oil (SBO), hydrogenated SBO (HSBO) and ultra low linolenic SBO (ULLSBO). Intermittent batch frying tests were conducted up to 55 h of frying, and then tortilla chips were aged up to 4 months at 25 °C. Frying oils were analyzed for total polar compounds to determine the frying stability of the oil. Tortilla chips were analyzed for hexanal as an indicator of oxidative deterioration and by sensory analysis using a trained, experienced analytical panel. Results showed no significant differences between the total polar compound levels for MO/ULLSBO and HSBO after 55 h of frying, indicating a similar fry life. However, total polar compound levels for ULLSBO and SBO were significantly higher than for either MO/ULLSBO or HSBO, indicating a lower oil fry life. Hexanal levels in aged tortilla chips fried in SBO were significantly higher than in chips fried in any of the other oils. Tortilla chips fried in MO/ULLSBO and HSBO had significantly lower hexanal levels than in chips fried in ULLSBO. A sensory analysis of rancid flavor intensity showed similar trends to those for hexanal formation. The chips fried in SBO had the highest rancid flavor intensity, with significantly lower hexanal levels in chips fried in HSBO and MO/ULLSBO. Based on these results, MO/ULLSBO not only had a good fry life but also produced oxidatively stable fried food, and therefore would be a healthful alternative to HSBO. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Acrylamide content of commercial frying oil

After Swedish researchers reported that heated foods such as potato chips and French fries contain acrylamide, the potential for health damage resulting from the consumption of these foods became a widespread concern. Used frying oils collected from food manufacturing companies were subjected to acrylamide determination using GC/MS-SIM, but the compound was not detected. Thus, we conclude that frying oil used in deep frying would not contaminate foodstuffs with acrylamide and that the recovered oil, much of which is used as a component of animal feeds, would be safe for livestock. Model experiments heating oil at 180 degrees C suggested that no acrylamide was formed either from a mixture of major amino acids exuded from frying foodstuffs and carbonyl compounds generated from oxidized oil, or from oil and ammonia generated from amino acids.     

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.     

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.     

Formation of short‐chain glycerol‐bound oxidation products and oxidised monomeric triacylglycerols during deep‐frying and occurrence in used frying fats

Heating fats and oils at high temperature in the presence of air, a common procedure in culinary practices such as frying, results in a complex mixture of oxidation products. These compounds may impair the nutritional value of the food. Among them, there is a growing interest in the group of oxidised triacylglycerol monomers because of their high absorbability. The main structures in this group include triacylglycerols (TG) containing short‐chain acyl groups formed by homolytic β‐scission of the alkoxy radicals coming from allylic hydroperoxides. In addition there are TG containing oxidised fatty acyl groups of molecular weight similar to that of their parent TG, i.e., epoxy, keto and hydroxy fatty acyl groups. In this review, the main routes of formation of oxidised TG monomers are detailed. Also, the most relevant advances in the analysis of intact TG molecules by high‐performance liquid chromatography coupled with mass spectrometry are discussed. Special attention is paid to the present analytical possibilities for accurate quantification of the most important oxidised compounds formed at high temperature. Both the need to convert fats and oils into simpler derivatives, thus concentrating the compounds bearing the oxidised structure, and the methylation procedure selected to avoid artefact formation are justified. Typical concentrations of short‐chain fatty acids, short‐chain aldehydic acids, short‐chain diacids, and monoepoxy fatty acids, ketoacids and hydroxyacids in frying oils from restaurants and fried‐food outlets, with polar lipids levels at the limit of rejection for human consumption, are given.     

Effect of γ-tocopherol on formation of nonvolatile lipid degradation products during frying of potato chips in triolein

Formation of undesirable odors and flavors during food processing operations is an important problem for the food industry. To determine the effect of γ-tocopherol on these negative attributes of fried food, we fried potato chips in triolein with 0, 100, or 400 ppm γ-tocopherol. Triolein extracted from potato chips was sampled for residual γ-tocopherol and nonvolatile degradation products after the chips were aged. RP-HPLC coupled to atmospheric pressure chemical ionization MS and size-exclusion chromatography was used to analyze, samples for degradation products in the triolein absorbed in potato chips as well as the fryer, triolein. MS results showed that γ-tocopherol reduced the production of nonvolatile degradation products in the triolein absorbed by the potato chips and in the triolein in the fryer. Fryer oil samples and extracted potato chip oils with 400 ppm γ-tocopherol had a significantly lower production of degradation compounds than did samples with 100 ppm γ-tocopherol. Both fryer oils and potato chips containing 100 ppm γ-tocopherol had significantly fewer nonvolatile degradation products than did the samples without γ-tocopherol. These nonvolatile compounds are known precursors of negative odors and flavor compounds produced during the frying and aging of foods.     

Sunflower Oil–Beeswax Oleogels Are Promising Frying Medium for Potato Strips

Sunflower oil–beeswax oleogels at 3% (BWO-3) and 8% (BWO-8) organogelator concentration are prepared to evaluate oleogels as frying medium for potato strip frying against commercial sunflower oil (SO). Rheological and thermal analyses of oleogels prove that the samples are fully solid (20±3 °C) and totally liquid (180 °C), and thermoreversible. Fresh and used (after frying) fat analyses show that free fatty acidity (FFA), peroxide value (PV) and total polar materials (TPM) are enhanced in all samples at the 7th h, but the relative enhancement levels are lower in oleogel samples. Potato strips fried in oleogels absorb significantly less oil (11.97% and 12.07%) than the control sample (15.20%). Potatoes fried in oleogels are also more bright and yellower than the control sample. Textural profile of the fried potatoes indicates that the samples fried in oleogels are harder, springier, and gummier than that of the control sample. Sensory analysis shows that oleogel fried potatoes get higher sensory scores. Also, overall acceptability of potatoes fried in BWO-8 sample is the highest (8.50) among all. The prepared oleogels are found quite promising frying medium in this study. Further studies with other types of oleogels in extended period frying of various foods are suggested. Practical applications: The development of innovative frying techniques to produce healthier products with lower fat and calorie values are still a remarkable research area. Oleogelation is an emerging strategy used for solid-like oil designing and based on the formation of 3D networks by the addition of organogelators. Oleogelation is accepted as a healthy strategy to structure liquid oils into solid consistency, and oleogels have great edible applications in processed foods, and can be used as a frying medium. This work can guide the use of sunflower oil–beeswax oleogels as a frying medium and allow the development of more healthy fried snacks.     

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.     

Oxidative Stability and Changes in Chemical Composition of Extra Virgin Olive Oils After Short‐Term Deep‐Frying of French Fries

We aimed at investigating oxidative stability and changes in fatty acid and tocopherol composition of extra virgin olive oil (EVOO) in comparison with refined seed oils during short‐term deep‐frying of French fries, and changes in the composition of the French fries deep‐fried in EVOO. EVOO samples from Spain, Brazil, and Portugal, and refined seed oils of soybean and sunflower were studied. Oil samples were used for deep‐frying of French fries at 180 °C, for up to 75 min of successive frying. Tocopherol and fatty acid composition were determined in fresh and spent vegetable oils. Tocopherol, fatty acid, and volatile composition (by SPME–GC–MS) were also determined in French fries deep‐fried in EVOO. Oil oxidation was monitored by peroxide, acid, and p‐anisidine values, and by Rancimat after deep‐frying. Differential scanning calorimetry (DSC) analysis was used as a proxy of the quality of the spent oils. EVOOs presented the lowest degree of oleic and linoleic acids losses, low formation of free fatty acids and carbonyl compounds, and were highly stable after deep‐frying. In addition, oleic acid, tocopherols, and flavor compounds were transferred from EVOO into the French fries. In conclusion, EVOOs were more stable than refined seed oils during short‐term deep‐frying of French fries and also contributed to enhance the nutritional value, and possibly improve the flavor, of the fries prepared in EVOO.     

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.