Determination of tocopherol in oxidized fats. Interference from heat-formed reducing substances in highly oxidized fats

Summary and Conclusions By application of a heating method to determine tocopherol in oxidized fats it was shown that polymeric reducing substances were produced when fats have a peroxide value exceeding 100. By comparison with a chromatographic method to remove peroxides it was shown that the interference in determining tocopherol from these heat-produced reducing substances was negligible at peroxide levels lower than 100. It is concluded that the heating method is satisfactory within the peroxide range (0–100) most important in oxidative and flavor-stability studies of edible oils. The chromatographic method for removing peroxides can be relied upon for determining tocopherol in more highly oxidized fats as well as in methyl esters of fatty acids which are distillable under conditions of the heating method. The appearance of reducing substances in heated oxidized fats is related to the peroxides present in the fats prior to heating. It is accompanied with an increase in browning, viscosity, acid, and carbonyl values of the fats and with a decrease in iodine values. The polymeric material from heated-oxidized methyl esters of unsaturated fatty acids has been separated by vacuum distillation and chromatography on silicic acid. It is believed to be principally dimeric in nature.     

Relationship of peroxide value and thiobarbituric acid value to development of undesirable flavor characteristics in fats

The peroxide value and thiobarbituric acid value were compared with the flavor score for a series of different types of fats, with and without added monoglyceride and with and without different stabilizers. The data indicated that the flavor score cannot be estimated for any given fat from either the peroxide value or the thiobarbituric acid value. Either can be used to follow the development of off flavors in a given product or formulation but the relative level may vary from product to product. Presented at the AOCS Meeting in Minneapolis, 1963.     

鸡脂控制氧化-热反应制备鸡肉香精

以过氧化值、茴香胺值和酸值表征鸡脂氧化状态,通过正交实验研究了氧化温度、氧化时间、空气流速等因素对鸡脂控制氧化的影响,确定了以制备肉味香精前体物为目标的鸡脂氧化较优工艺:氧化温度120℃、氧化时间2 h、空气流速0.025 m3/(h.100 g脂肪)。热反应条件固定为加热温度110℃,时间40 m in,w(氧化鸡脂)=1%,感官评价了各氧化鸡脂的热反应产物气味特征,确定了鸡脂控制氧化-热反应制备鸡肉香精的氧化鸡脂工艺指标:过氧化值200~600 mmol氧/kg脂肪,茴香胺值105~330,酸值<4.7 mg KOH/g脂肪。     

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.     

Lipoxidase deactivation to improve stability,odor and flavor of full-fat soy flours

Oxidation of soybean lipids catalyzed by lipoxidase was prevented by heat treatment of soybean meats, which were then ground to give a full-fat soy flour free of rancid odor and flavors. Our previous studies showed that lipids in cracked, dehulled, soybeans rapidly oxidized after the lipoxidase system was activated by increasing moisture content to 20%. A series of experiments are reported in which various heat treatments were evaluated for effectiveness of lipoxidase deactivation. Dry heat to 212 F, steaming, or both, deactivated lipoxidase to give flours that had low values of peroxide, conjugated diene and free fatty acid and had good flavors after 2 years’ storage. Wet heat alone was also an effective treatment, whereas wet heat preceded by dry heat at 180 F gave poor flavor stability after 2 years. Gas liquid chromatography studies gave evidence that the rapid formation of volatiles in full-fat soy flours was catalyzed by an enzyme system. A 10 member taste panel was able to detect significant flavor and odor differences between oxidized and nonoxidized samples. Presented at the AOCS Meeting, Chicago, October 1967. No. Utiliz. Res. Dev. Div., ARS, USDA.     

AOCS collaborative study on sensory and volatile compound analyses of vegetable oils

An AOCS collaborative study was conducted to determine the effectiveness of sensory analysis and gas chromatographic analyses of volatile compounds in measuring vegetable oils for levels of oxidation that ranged from none to high. Sixteen laboratories from industry, government, and academia in Canada and the United States participated in the study to evaluate the flavor quality and oxidative stability of aged soybean, corn, sunflower, and canola (low-erucic acid rapeseed) oils. Analytical methods included sensory analyses with both flavor intensity and flavor quality scales and gas-chromatographic volatiles by direct injection, static headspace, and dynamic headspace (purge and trap) techniques. Sensory and volatile compound data were used to rank each of the oils at four levels of oxidation—none, low, moderate, and high. For soybean, canola, and sunflower oils, 85–90% of laboratories correctly ranked the oils by either analysis. For corn oil, only 60% of the laboratories ranked the samples according to the correct levels of oxidation by either analysis. Variance component estimates for flavor scores showed that the variation between sensory panelists within laboratories was lowest for the unaged oils. As storage time increased, the variance also increased, indicating that differences among panelists were greater for more highly oxidized oils. Between-laboratory variance of sensory panel scores was significantly lower than within-laboratory variance.     

A long-term nutritional study with fresh and mildly oxidized vegetable and animal fats

Fresh and oxidized cotton seed oil (CO) olive oil (OO), chicken fat (CF) and beef fat (BF) were fed to male weanling rats for 33 to 108 weeks. Groups fed oxidized fats except OO showed a higher death rate than those fed the corresponding fresh fats. Groups fed oxidized CO and BF had the highest death rate. Histological studies of animals dying from natural causes showed more pronounced cardiac lesions in the animals fed oxidized CO. Serum, liver and brain cholesterol levels were not influenced by oxidized fats. Fatty acid composition of depot fats and of heart and liver lipids did not show significant differences between groups fed fresh and the corresponding oxidized fats. Presented at the Spring Meeting of the AOCS 1964.     

The use of thiobarbituric acid as a measure of fat oxidation

Summary An evaluation of thiobarbituric acid (TBA) as an agent for the measurement of fat oxidation was made by the application of several empirical procedures to animal and vegetable fats. An extraction procedure was used for removing the products of oxidation. The reaction with TBA was conducted in a boiling water bath to produce a red color, which was then estimated spectrophotometrically. Fats stored at −20, 0, 72, and 100°F. (−29, −18, 22, and 38°C.) and fats oxidized by the active oxygen method (A.O.M.) and by ultraviolet irradiation were examined. It was found that the TBA test might be of value in following the course of oxidation of cottonseed oil and soybean oil in the A.O.M. apparatus. Higher TBA values were obtained for soybean oil than cottonseed oil at comparable peroxide values. This is of interest because of the greater tendency of soybean oil to develop oxidized flavors. The volatile reaction products of oxidation were collected in toluene, and a comparison of the TBA values at comparable peroxide values of lard, cottonseed and soybean oils showed that the soybean oil volatiles developed the greatest intensity of color. Presented at the 27th Fall Meeting of the American Oil Chemists’ Society, Chicago, Ill., Nov. 2–5, 1953. This paper represents research undertaken by the Quartermaster Food and Container Institute for the Armed Forces and has been assigned No. 450 in the series of papers approved for application. The views and conclusions contained in this paper are those of the authors. They are not to be construed as necessarily reflecting the views or indorsement of the Department of Defense.     

Formation of headspace volatiles by thermal decomposition of oxidized fish oilsvs. oxidized vegetable oils

To understand the reasons for differences in oxidative stability among edible oils, the temperature dependence was investigated for the development of volatile lipid oxidation products in fish oils and in vegetable oils. A rapid headspace capillary gas chromatographic method was developed to determine volatile oxidation products of omega-6 (n-6) polyunsaturated fats (pentane and hexanal) and omega-3 (n-3) polyunsaturated fats (propanal) at different decomposition temperatures. Headspace gas chromatographic analyses of partially oxidized menhaden, bonita and sardine oils could be performed at 40°C, whereas soybean, canola, safflower, high-oleic sunflower and high-oleic safflower oils required temperatures greater than 100°C. Volatile formation by thermal decomposition of oxidized oils had lower apparent activation energies in fish oils than in vegetable oils, and significantly higher apparent activation energies in high-oleic oils than in polyunsaturated oils. The activation energy data on headspace volatiles provided another dimension toward a better understanding of the thermal stability of flavor precursors in unsaturated fish and vegetable oils. Presented at the ISF/AOCS joint meeting, Toronto, Canada, May 10–14, 1992.     

Fatty acid composition of heart cells exposed to thermally oxidized fats

Corn oil and olive oil were thermally oxidized, and the free fatty acids from the fresh fats, and from the distillable non-urea-adductable (DNUA) fractions of the thermally oxidized fats were prepared. These were added as emulsions to the medium of primary cultures of heart endothelial and muscle cells from neonatal rats. After exposure for 24 hr, the fatty acid composition of the triacylglycerol (TC) and phospholipid (PL) fractions of the cells was determined. Reflecting the nature of the fat used, the corn oil treatment produced relatively higher concentrations of linoleic acid in the TG and PL fractions compared to the olive oil treatment, in which case the oleic acid level was influenced. Treatment of the cultured cells with components derived from oxidized corn oil or oxidized olive oil resulted in lower concentrations of linoleic and arachidonic acids in the PL moieties compared to the fresh fat controls. However, there were marked increases in arachidonic acid in the TG fractions of both the endothelial and muscle cells. These changes due to the DNUA from thermally oxidized fats indicate a distinct metabolic response to the derivatives formed during thermal oxidation of the fats.     

Uptake and utilization of 1-14C palmitic acid by heart cells treated with fresh or thermally oxidized fats

The effects of fractions isolated from thermally oxidized corn oil or olive oil on the metabolic activity of heart endothelial and muscle cells were studied. Rat heart cells in culture, exposed to thermally oxidized fat components, took up more exogenous 1-¹⁴C-palmitic acid and incorporated more of it into the cell triacylglycerol fraction than when the cells were treated with fresh fats. Particularly with the heated corn oil compared to fresh corn oil, much less of the radioactivity from the labeled palmitic acid was deposited in the phospholipid fraction. Also, with heated corn oil when the incubation period was extended beyond 12 hr, there was a decline in the radioactivity retained in the triacylglycerol fraction of the heart muscle cells. When the fresh fats were compared for¹⁴C-radioactivity incorporation into the heart cells, the olive oil gave much higher values, indicating a distinct difference in response to the proportion of fatty acids supplied. Presented in part at the AOCS Meeting, Chicago, September 1976.     

Comparison of a simplified,quantitative kreis test with peroxide values of oxidizing fats

Summary 1. A simplified quantitative Kreis test has been compared with peroxide numbers and iodine values during prolonged rancidification of several animal and vegetable fats. 2. The ratio of Kreis to peroxide values varied with the kind of fat and seemed to parallel its linoleic acid content. With vegetable oils containing a large amount of linoleic acid (corn and cottonseed) the intensity of color at the time of peak color development was too great to be read on the colorimeter. 3. With all fats for which accurate determinations were possible (butter, chicken, pork, and ethyl oleate), the Kreis values reached maximum and began falling off while peroxide values were still increasing. 4. Temperature of fat storage had a greater effect on the Kreis test than on the peroxide number. Increasing the temperature caused a decrease not only in the peak values obtained for the Kreis test, but also in the ratio of Kreis to peroxide values. Published as Scientific Paper No. 670, College of Agriculture and Agricultural Experiment Stations, State College of Washington, Pullman.     

Effects of dietary thermoxidized fats on expression and activities of hepatic lipogenic enzymes in rats

This study was undertaken to investigate the effect of dietary oxidized fats on the relative mRNA concentrations and the activities of fatty acid synthase (FAS) and glucose-6-phosphate dehydrogenase (G6PDH) in the liver of rats treated with vitamin E or selenium. Two experiments with male Sprague-Dawley rats were carried out. The first experiment included eight groups of rats fed diets with either fresh fat or three different types of oxidized fat, preparated by heating at temperatures of 50, 105, or 190°C, over a period of 6 wk. The diets contained either 25 or 250 mg α-tocopherol equivalents per kg. The second experiment included four groups of rats fed diets with fresh fat or oxidized fat, heated at a temperature of 55°C, containing either 70 or 570 μg selenium per kg, over a period of 8 wk. Feeding the diets with oxidized fats led to a significant overall reduction of the relative mRNA concentrations and the activities of FAS and G6PDH in both experiments. The effects of the oxidized fats on mRNA concentrations and activities of these enzymes were independent of the dietary concentrations of vitamin E or selenium. Moreover, in both experiments the rats whose diet contained the oxidized fats had significantly lower concentrations of TG in liver, plasma, and VLDL than the rats whose diet contained fresh fat. The study suggests that oxidized fats contain substances that suppress gene expression of lipogenic enzymes in the liver.     

The use of electronic and human nose for monitoring rapeseed oil autoxidation

This work was aimed at assessing the effectiveness of the electronic nose to monitor off‐flavor associated with lipid oxidation as a supplementary tool to human sensory panel assessment. Therefore, correlations between electronic nose and sensory analysis were determined. Also GC analyses and chemical analyses of oil samples were run to characterize the analyzed samples with well‐described parameters. Refined rapeseed oil was subjected to an accelerated storage test for 12 days at 60 °C and to an ambient temperature storage test in which it was stored in retail plastic bottles for up to 6 months. PCA of electronic nose data samples stored at an elevated temperature was related to PCA of sensory analysis, and similarities in sample clustering were observed. For samples stored at room temperature, the human panel showed greater sensitivity than the electronic nose. Prediction models based on PLS of electronic nose data were able to predict the sensory quality changes during storage at elevated and room temperature, ranging from 0.721 to 0.989 and from 0.849 to 0.881 (p <0.05), respectively. PV and p‐AV were well predicted on the basis of both electronic nose (0.989, 0.998 for elevated temperature; 0.907, 0.881 for room temperature) and sensory analysis data (0.973, 0.993 for elevated temperature; 0.939, 0.886 for room temperature). Applicability of the electronic nose technology to verify sensory and rancidity changes during storage showed to be promising in quality control of oils.     

Zur Analytik und Beurteilung von Fritürefetten III Beobachtungen aus der Praxis der Lebensmittelüberwachung

Analysis and Assessment of Frying Fats III: Observations from the Practice of Food Surveillance Based on frying experiments and analyses of frying fats from processing plants the criteria were laid that are suitable for legal assessment of the degree of spoilage of frying fats which have either been used too long or have been overheated. Determination of the oxidized fatty acids that are insoluble in petroleum ether was found to be a reliable basis for the objective assessment whether a frying fat was edible or spoiled. Absolute limits which, according to § 4, 2 of the Food Law, indicate the values beyond which the edible frying fat is considered to be spoiled were specified as follows: 0.7% Oxidized fatty acids that are insoluble in petroleum ether, smoke point < 170° C at smoke point differences ≥ 50° C, and acid values > 2 5. After attaining the aforementioned values the frying fats are altered to such an extent that their non-edible quality can be established even by sensory tests (smell, taste, appearance). It was found that also the manufacturers of fried foods are able to recognize such alterations in smell, taste and discoloration of frying fats well in time to renew such fats. Within the jurisdiction of the Chemical Investigations Laboratory of the city of Bochum (5 cities) no serious objections were raised to any one of the products which were assessed by the laboratory and found to be spoiled. The law courts accepted the specified limits and the number of samples found objectionable diminished rapidly. (It should be noted that in October 1973 ALS supported these specifications as limiting values which objectively correspond to the actual sensory findings.)     

Oxidation and quality of soybean oil: A preliminary study of the anisidine test

The anisidine test, a measure of secondary oxidation products in glyceride oils, was applied to a number of soybean salad oils processed from sound and damaged soybeans. A highly significant correlation (−0.68) was found between the anisidine values of salad oils from sound soybeans and their flavor scores. Multiple correlations between flavor scores, anisidine, and peroxide values yielded a correlation of 0.81 and provided a method for predicting the initial flavor scores of sound soybean salad oils. Similar data for oils from damaged beans gave a highly significant, but lower, correlation (−0.65). Comparative studies indicated that sound crude oils usually contain lower levels of oxidation products than damaged crude. Oxidation in both sound and damaged crudes increased roughly in proportion to iron content. Reproducibility of the test and the effects of hydrogenation, accelerated storage, and fluorescent light on anisidine values were studied. Analysis of damaged oils before and after deodorization showed that little, if any, reduction of anisidine value occurred. Deodorization of sound oils, however, lowered anisidine values. In comparison with damaged oils, the anisidine values of sound oils were lower at comparable stages of processing. The poor quality of damaged soybean oil was substantiated by organoleptic evaluations. Flavor scores of oils given special processing treatments increased as anisidine values decreased.     

Quality assessment of used frying fats: A comparison of four methods

The level of petroleum ether insoluble oxidized fatty acids in used frying fats is one of the recommended criteria for assessing their quality in Germany; however, the method of determination is time consuming and inaccurate. Gel permeation chromatography (GPC) allows the determination of dimeric and oligomeric triglycerides in a heated fat irrespective of the presence of oxidized material. An indication of the total amount of polar and oxidized compounds can be obtained by liquid chromatography (LC) on a silica gel column in connection with a moving-wire detector. A comparatively simple and quick method is the separation of polar and unpolar components in a used frying fat by means of column chromatography (CC) on silica gel. Over a large number of investigations, a good correlation was seen between the results obtained with GPC, LC, and CC and the amount of petroleum ether insoluble oxidized fatty acids isolated from used frying fats. Limits of the analytical data obtained by the new methods are proposed which indicate deterioration of used frying fats.     

Flavor stability of high-oleic peanuts stored at low humidity

Shelf-life studies were conducted on roasted high-oleic peanuts (HOP; F1250, BC93Q10) and a reference peanut with normal oleic acid content (NOP, Florunner). HOP contained at least 80% oleic acid and 3% linoleic acid, whereas normal-oleic peanuts contained 53% oleic and 27% linoleic acids. Peanuts were dry-roasted to a medium roast (Hunter lab L=50) and stored at 40°C at 18% relative humidity. Samples were removed from storage at different intervals (0, 2, 4, 7, and 10 wk) for sensory evaluation and chemical oxidation measurements. Sensory attributes rated included roasted peanutty flavor, sweetness, crunchiness, and oxidized flavors (cardboardy and painty). The two HOP lines were not significantly different from each other in flavor quality or stability during storage but had better flavor quality and stability than NOP. The latter oxidized faster and developed painty off-flavors to a greater extent than did the HOP lines. Chemical oxidation measurements confirmed higher levels of oxidation in NOP than in the HOP lines. Peroxide values at 10-wk storage were 47 meq/kg oil for NOP and <3 meq/kg oil for the HOP lines. Both HOP lines had greater shelf lives than NOP.     

Problems arising in connection with the use of antioxidants in the food industry

Summary Investigations on the use of the gallic acid esters, butylated hydroxyanisole, and butylated hydroxytoluene as antioxidants in animal fats, vegetable oils, margarine, and bakery products are described. It was found that the gallates and BHT were highly effective in lard; BHA was of lesser importance. In vegetable oils scarcely any effect was observed although some antioxidants might be able to suppress peroxide formation in these products; the flavor evaluations however are not always in accordance with these findings. In margarine it was found that some antioxidants had a promising effect on the peroxide formation but only a slight effect on the flavor. Mixtures of antioxidants however could exercise a synergistic effect on the organoleptic qualities. In bakery products,e.g., Dutch shortbread, BHT can afford good protection against flavor deterioration. Mention is made of the fact that the dissociation of peroxides is governed primarily by their concentration and that fats with a peroxide value of 25 to 50 meq/kg. are very stable on heating at 100°C. without air-passage. Lecture delivered at the symposium on antioxidants, organized by the Low Temperature Research Station, Cambridge, April, 1957.     

Characteristics of the thiobarbituric acid reactivity of oxidized fats and oils

The thiobarbituric acid (TBA) reactivity of oxidized methyl linoleate, soybean oil, sesame oil, lard, chicken oil and sardine oil was characterized by using four different methods with 0.01% butylated hydroxytoluene (BHT). Optimal pH for the reactivity of most of the oxidized samples was 3–4, and that of some samples was above 5. Introduction of 2 mMt-butyl hydroperoxide (t-Bu00H) or 0.2 mM ferric ion in the reaction markedly enhanced the reactivity. Introduction of 0.2 mM ethylenediamine tetraacetic acid suppressed the reactivity. The characteristics of the TBA-reactivity of the samples were similar to those of alkadienals or alkenals. The most preferable method for the estimation of the TBA-reactive substances of the oxidized fats and oils was that using solvents at pH 3.5 with introduction of BHT, andt-Bu00H or ferric ion.