Nutrition quality of frying fats in commercial use

Summary and Conclusions Publications on fats heated in the laboratory have been critically reviewed, and many of the these have been shown to present findings irrelevant to commercial frying operations. Just about two weeks before the delivery of this paper Rice and associates (22) independently reported before the American Institute of Nutrition on the nutritive value of frying oils in commercial use. They too were critical of the results of studies of highly unsaturated fats heated under unrealistic, arbitrarily selected, laboratory conditions. Conclusions based upon such laboratory studies should not be extended beyond the scope of the findings reported. The present report has presented the results of a nation-wide survey of the frying oils in use on a continuing basis in the potato chip industry. Whereas a 1% decrease in iodine value has been found in the heated oils, this change has been shown to have no nutritional significance. The constancy in composition of the frying oils, heated as compared to fresh, and the results of physico-chemical studies support the conclusion that neither thermal polymers nor thermal oxidative polymers are present in the oils employed in the commercial frying operations. Notrans fatty acids develop during the heating operations. The changes in linoleic acid content, the essential fatty acid in vegetable oils largely responsible for the important noncaloric functions of fat in the diet (23,24), are too small to have nutritional significance. This permits the same conclusions to be made in regard to the nutritive value of the heated oils,i.e., of the triglycerides contained therein, as have been drawn from studies conducted on the corresponding fresh oils. Presented in the symposium on Fats in Nutrition and Health at the 48th Annual Meeting, American Oil Chemists' Society, New Orleans, April 30, 1957. For a more extensive review of the subject the reader is referred to a paper published in J. Am. Oil Chemists' Soc.,34, 351–356 (1957). In this paper and in another submitted to the same Journal will be found additional experimental details and findings to support conclusions drawn.     

Composition and control of potato chip frying oils in continuing commercial use

Summary The oils in use on a continuing commercial basis in the production of potato chips on a nation-wide scale are found to be free of thermal polymers. This conclusion is supported by the similarity in physical properties and in chemical composition between the fresh and heated oil in any one operation. In a) degree of unsaturation of oils, b) melting point, c) setting point, d) fatty acid composition, e) free fatty acid content, f) concentration of fatty acid isomers, g)solids content index, and h) in the crystallizing properties of the oils, there are no differences between fresh and heated oil of such magnitude to warrant criticisms of the wholesomeness of the oil being absorbed by the chip. The constancy in composition between heated and fresh oil, particularly with respect to the essential fatty acid content, which is largely responsible for the noncaloric functions of fats in the diet (19), permits the same conclusions to be made in regard to the nutritive value of the heated oils,i.e., of the triglycerides contained therein, as have been drawn from studies conducted on the corresponding fresh oils. Based upon statistical quality control considerations, the oils employed in the survey of the potato chip industry have been characterized by having a free fatty acid value of no greater than 0.60% and a decrease in iodine value of no greater than 3.0% in 95% of the operations. These control limits characterize the oils, which, on test, have led to the generalization about the absence of thermal polymers in commercial potato chip frying oils. Much of the material in this paper and in one recently published (1) was presented at the 48th Annual Meeting of the American Oil Chemists' Society in the Symposium on “Fats in Nutrition and Health,” New Orlens, La., April 30, 1957.     

Pan-frying stability of NuSun oil,a mid-oleic sunflower oil

Pan-frying is a popular frying method at home and in many restaurants. Pan-frying stabilities of two frying oils with similar iodine values (IV)—mid-oleic sunflower oil (NuSun oil; IV=103.9) and a commercial canola oil (IV=103.4)—were compared. Each oil sample was heated as a thin film on a Teflon-coated frying pan at ∼180°C to a target end point of ≥20% polymer. High-performance size-exclusion chromatography analysis of the mid-oleic sunflower and canola oil samples indicated that the heated samples contained 20% polymer after approximately 18 and 22 min of heating, respectively. The food oil sensor values increased from zero to 19.9 for the canola sample and from zero to 19.8 for the mid-oleic sunflower sample after 24 min of heating. The apparent first-order degradation rate for the mid-oleic sunflower sample was 0.102±0.008 min⁻¹, whereas the rate for the canola sample was 0.092±0.010 min⁻¹. The acid value increased from approximately zero prior to heating to 1.3 for the canola sample and from zero to 1.0 for the mid-oleic sunflower sample after 24 min of heating. In addition, sensory and volatile analyses of the fried hash browns obtained from both oils indicated there were no significant differences between the two fried potato samples.     

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.     

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.     

Anomalous high iodine value of squalene and the impact on iodine values of shark liver oils

Squalene has six ethylenic bonds, but the experimental iodine values in two different solvent systems—chloroform and cyclohexane/acetic acid—were 25% higher than the theoretical values. We propose that this results from an additional halogen adding at each of the two terminal ethylenic bonds carrying two methyl groups. In the solvent system of cyclohexane alone, the excess is only 3–4% greater than the theoretical. Mixtures of squalene in seal oil confirmed the additivity of the experimental squalene high iodine value and the seal oil fatty acid iodine value with reasonable accuracy but depended on the skill of the operator in obtaining the titration end point for cyclohexane/acetic acid. This observation has particular relevance for shark liver oils and olive oils.     

Anomalous high iodine value of squalene and the impact on iodine values of shark liver oils

Squalene has six ethylenic bonds, but the experimental iodine values in two different solvent systems—chloroform and cyclohexane/acetic acid—were 25% higher than the theoretical values. We propose that this results from an additional halogen adding at each of the two terminal ethylenic bonds carrying two methyl groups. In the solvent system of cyclohexane alone, the excess is only 3–4% greater than the theoretical. Mixtures of squalene in seal oil confirmed the additivity of the experimental squalene high iodine value and the seal oil fatty acid iodine value with reasonable accuracy but depended on the skill of the operator in obtaining the titration end point for cyclohexane/acetic acid. This observation has particular relevance for shark liver oils and olive oils.     

Specific Heat Capacity Measurements of Frying Oil Using Modulated Differential Scanning Calorimetry

The specific heat capacity (c_p) of frying oils is of practical importance in engineering work associated with refining operations and the thermal resistance during application. The objective of this study was to use modulated differential scanning calorimetry (MDSC) to measure the specific heat capacity of frying oil. Samples were exposed to a cyclic heating profile that was generated by a linear heating rate while simultaneously superimposing a sinusoidally varying time–temperature wave. The c_p variation of three commercial frying oils during frying was tested over a temperature range between 0 and 250 °C, and the correlation of c_p with triacylglycerol (TAG) polymer contents, total polar compounds (TPC), and polar fractions was studied. Results indicated that the specific heat capacity of frying oils increased linearly as temperature increased. During frying, c_p had a positive relation with TAG polymers and TPC at the beginning, but finally decreased when frying ended. This was possibly associated with the variation of polar fractions as frying continued. The large molecular compounds and small molecular compounds of polar fractions were considered to contribute oppositely to c_p, which led to its final decrease.     

Analysis of FFA in edible oils by catalyzed end-point thermometric titrimetry (CETT)

A novel titrimetric procedure has been developed for the determination of FFA in edible oils using an automated thermometric titration with KOH in isopropanol as titrant. The end point is indicated by the strongly exothermic base-catalyzed reaction between acetone and chloroform. The procedure is fast, easy to use, accurate, and highly reproducible. Analytical precisions (as one SD) in the range 0.001–0.003% w/w (as oleic acid) for new and used cooking oils were obtained. It is very suitable for the routine process and quality control of new and used oils in commercial frying operations, among other applications.     

Room odor evaluation of oils and cooking fats

Panel evaluations have been made of room odors developed by edible oils and cooking fats heated to frying temperatures. Vegetable and mixed fat shortenings, as well as oils of different iodine value and from special processing, were investigated with and without added stabilizers. When silicones were added to frying fats, room odor scores improved markedly. Certain added autoxidative cleavage products had little effect on odor scores at levels where they were detected easily in taste tests. To be discernible in room odors, these additives had to be present at levels ca. 100-fold greater than their taste thresholds. Panel results show that the undesirable frying odors contributed by unhydrogenated soybean oil in mixtures with other oils could be detected readily at 25% levels. As the level of soybean oil was lowered further, the room odor scores of oil mixtures improved perceptibly. One of 13 papers presented in the symposium “Flavor Research in Fats and Fat Bearing Foods,” AOCS Meeting, Atlantic City, October 1971. N. Market. Nutr. Res. Div., ARS, USDA.     

Membrane processing of used frying oils

Studies were conducted with used frying oils in a flat membrane batch cell using five different types of polymeric membranes to decrease the soluble degradation products. During membrane processing, triglycerides permeated preferentially compared to the majority of the polar compounds including oxidation products, polymers, and color compounds. Two of the composite membranes, NTGS-AX and NTGS-2200, selectively rejected polar compounds and oxidation products to the extent of 25–48% and 24–44% respectively. The reduction in Lovibond color values (5R+Y) was in the range of 83–93%. The viscosity of the used frying oil was reduced to the extent of 22%. The composite membranes were effective in reducing the soluble impurities, as well as insoluble particulates, without causing any undesirable changes to the oil. The membrane process appears to improve the life of used frying oils and does not have the disadvantages associated with the active filtration systems, however, for commercial application the permeate flux needs to be improved considerably.     

Oxidative stability of healthful frying oil medium and uptake of inherent nutraceuticals during deep frying

Four healthful frying oil mediums have been formulated using sunflower (FOB-I), groundnut (FOB-II), mustard (FOB-III), and palm olein (FOB-IV) oils as base oils, and fortified with rice bran and crude sesame oils separately in the ratio of 60∶20∶20 (by vol). Oxidative stabilities have been ascertained by deep-frying potato bajji (potato slices sandwiched with Bengal gram flour) continuously for 60 min for three cycles with a gap of 7 d each. The product had moisture between 12.8 and 16.0% and absorbed fat between 32.5 and 38.1%, making the oil media vulnerable to oxidation. The p-anisidine values for leftover FOB-I and FOB-IV ranged from 10.8 to 24.4 and from 1.5 to 10.7, respectively, indicating that the former was a less and the latter a more stable combination. Hydroperoxide and conjugated dienes were assessed by UV spectrometry at λ_max 230 nm. The O.D. was maximal (1.4) for FOB-I samples for both leftover and absorbed oils for third-cycle experiments. That there was no absorbance for the FOB-III and-IV samples indicated their absence. Estimation of oryzanol and sesamol in oil left over after deep frying and in the oil absorbed by the products indicated that distribution was equal and there was no loss of these active factors during deep frying. The study indicated that sunflower oil blend was the least stable and the palm olein blend was most stable.     

A simple,graphic procedure for authentication of commercial fats and oil based on fatty acid compositions in codex standards

It is likely that fatty acid compositions as derived by gas liquid chromatography will soon become one of the mandatory criteria for authentication of individual (unmodified) commercial fats and oils in the standards of the Food and Agriculture Organization/ World Health Organization’s Codex Alimentarius Committee on Fats and Oils. A simple graphical procedure for using the Codex Committee’s fatty acid composition standards to identify fats and oils has been devised and tested. Except for one sample, the fatty acid-based standards have not been found to conflict with some presently accepted mandatory standards (i.e, iodine value, refractive index, and saponification value).     

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.     

Effect of a modified deep-fat fryer on chemical and physical characteristics of frying oil

We designed a modified deep-fat fryer (MDF) to have a smaller oil area (A) relative to depth or height (H) such that H/√A=0.93. The modification was intended to retard the thermal degradation of the frying oil and the production of waste oil. Frozen croquettes were fried in vegetable oil using the MDF (H/√A=0.93) and three conventional deep-fat fryers (CDF1, H/√A=0.25; CDF2, H/√A=0.20; CDF3, H/√A=0.30) at 180°C for 72 h at 8 h/d. Frying oils were periodically collected, and their chemical and physical characteristics were examined. The acid value (AV) of frying oils used for 72 h in the MDF was lower than that for oils used in the CDF, although the AV was similar in all fryers until 32 h. The oil deep-fried with MDF had a higher degree of color than that with CDF until 48 h. Polymerized materials and the carbonyl value of frying oil after heating 72h with MDF were lower than those with CDF. The residual tocopherol content of frying oil with MDF was 83% of the content in fresh oil, whereas with CDF the tocopherol contents were less than 63%. The oil consumption by MDF was less than that by CDF, although the turnover rate was higher in MDF than in CDF. These results suggest that during deep-fat frying the MDF may retard the thermal deterioration of vegetable oils and generate less waste oil.     

Analysis of thermally abused soybean oils for cyclic monomers

Cyclic monomers derived from the intramolecular condensation of the C₁₈ polyunsaturated fatty acids have been reported to elicit toxic responses when fed to laboratory animals at low dietary levels. This study was undertaken to quantitate the cyclic monomers formed by thermal oxidation induced during deep fat frying to assess the potential toxicity of commonly used vegetable oils. Two separate experiments were designed to study the effects of unsaturation and both intermittent and continuous heating on cyclic monomer formation. Both lightly hydrogenated soybean oil (iodine value [IV]=107) and refined, bleached and deodorized soybean oil were studied. The heated oil sustained substantial chemical and physical alterations, as indicated by IV decreases from 10–15 units, increases in free fatty acids of 5–10-fold and in noneluted material of 18–21%. Selected samples were completely hydrogenated and analyzed for cyclic monomers by gas chromatography. Under chromatographic conditions sufficiently sensitive to detect a cyclic monomer standard at less than 0.5% by weight, no cyclic monomers were detected in any of the heated oil samples. However, after concentration by low temperature crystallization of the hydrogenated samples to remove a major portion of the saturated components interfering in cyclic monomer resolution, about 0.3–0.6% cyclic acids, as well as 0.4–0.9% polar materials, were detected in the heated soybean oils. Components appearing in the gas chromatogram with the same retention time as those in a cyclic monomer standard were further identified by gas chromatography-mass spectrometry as disubstituted cyclic C-18 acids.     

Low-linolenic acid soybean oil—Alternatives to frying oils

Oil was hexane-extracted from soybeans that had been modified by hybridization breeding for low-linolenic acid (18∶3) content. Extracted crude oils were processed to finished edible oils by laboratory simulations of commercial oil processing procedures. Oils from three germplasm lines N83-375 (5.5% 18∶3), N89-2009 (2.9% 18∶3) and N85-2176 (1.9% 18∶3) were compared to commercial unhydrogenated soybean salad oil with 6.2% 18∶3 and two hydrogenated soybean frying oils, HSBOI (4.1% 18∶3) and HSBOII (<0.2% 18∶3). Low-18∶3 oils produced by hybridization showed significantly lower room odor intensity scores than the commercial soybean salad oil and the commercial frying oils. The N85-2176 oil with an 18∶3 content below 2.0% showed no fishy odor after 10 h at 190°C and lower burnt and acrid odors after 20 h of use when compared to the commercial oils. Flavor quality of potatoes fried with the N85-2176 oil at 190°C after 10 and 20 h was good, and significantly better at both time periods than that of potatoes fried in the unhydrogenated oil or in the hydrogenated oils. Flavor quality scores of potatoes fried in the N89-2009 oil (2.9% 18∶3) after 10 and 20 h was good and equal to that of potatoes fried in the HSBOI oil (4.1% 18∶3). Fishy flavors, perceived with potatoes fried in the low-18∶3 oils, were significantly lower than those reported for potatoes fried in the unhydrogenated control oil, and the potatoes lacked the hydrogenated flavors of potatoes fried in hydrogenated oils. These results indicate that oils with lowered linolenic acid content produced by hybridization breeding of soybeans are potential alternatives to hydrogenated frying oils.     

Explorative spectrometric evaluations of frying oil deterioration

The potential of spectroscopy as a reliable and fast method for determining the deterioration of frying oils was investigated. Daily oil samples were collected from a commercial Chinese spring roll plant. The plant was operated one shift, 5 d a week, then cleaned and restarted with fresh oil every 4 wk. Each oil sample was analyzed by 11 chemical/physical methods and fluorescence, near infrared/visible (NIR/VIS), Fourier transform infrared (FT-IR) and FT-Raman spectroscopic procedures. The results were evaluated and compared by principal-component analysis and partial least squares regression. Most chemical/physical and all spectroscopic methods detected the deterioration during the first half of the frying cycle. Thereafter, an equilibrium occurred between deterioration processes and replenishment with new oil. At equilibrium, the correlation between frying time and the various methods was nonlinear. FT-IR with the attenuated total reflectance sampling technique was the most direct and accurate method of monitoring gross changes in the frying oil. Fluorescence was the technique that provided the best models for anisidine value, oligomers, iodine value, and vitamin E. NIR/VIS spectroscopy proved to be a good general-purpose technique. The study demonstrated that spectroscopic sensors have the potential to replace titration and chromatographic procedures, and can be used in combination with chemometric data analysis to optimize deep-frying operations.     

Fatty acid methodology for heated oils

Criticisms have been voiced concerning the methods employed for determining the fatty acid composition of vegetable oils used in processing of fried foods. In the present study seveveral different vegetable oils were heated under standardized conditions, at frying temperatures and under air, for various periods of time, and then subjected to analyses for fatty acid composition. The methods employed were: UV spectrophotometry; gas-liquid chromatography (GLC) employing either normalization of the peak areas, direct standards or internal standards; and the enzymic, lipoxidase procedure. The present findings confirm that the drop in iodine value is a good approximation of the reduction of polyunsaturated fatty acids in heated oils. In evaluating liquid nonhydrogenated vegetable oils that had been subjected to heat abuse under standard conditions, all of the analytical methods for the estimation of fatty acid composition, with the exception of normalization of GLC peak areas, give substantially the same results. With hydrogenated vegetable oils, the analytical methods provide values which differ significantly among themselves. Evidence was also presented to show that the quantity of material retained on the gas chromatographic column is directly related to the loss of polyunsaturates for oils heated under controlled conditions. For evaluation of oils from frying operations, the preferred method is the GLC method utilizing internal standards if the purpose is the determination of total polyunsaturated fatty acids. However, if the study being made involves a question of nutritional value, then the measurement of the essential fatty acids by the lipoxidase enzymic procedure is the more valid method for evaluation, of heated oils. Presented at the AOCS Meeting, New Orleans, April 1970.     

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.