Spectrophotometric determination of small proportions of polyunsaturated constituents in fatty materials

Summary Existing ultraviolet spectrophotometric methods have been modified for application primarily to the detection and estimation of low proportions of conjugated and nonconjugated unsaturated constituents in fats, oils, and soaps. The method is applicable also to fatty materials having high proportions of these constituents. Modifications include corrections for absorption by interfering substances, use of alkaline glycerol as an isomerization medium in the analytical procedure, and correction of absorption data on the isomerized product for absorption by conjugated constituents in the material before isomerization. The presence of small proportions of highly unsaturated conjugated and nonconjugated compounds is established in lards, tallows, tallow soaps, and highly purified esters and acids. Tall oil fatty acids are shown to contain approximately 10% of conjugated diene acids and a small amount of linolenic acid. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.     

Methods for stability and antioxidant measurement

A great variety of books and technical papers has been published dealing in detail with the basic chemistry of rancidity in fats and oils and the techniques which have been investigated as a means of determining the stability characteristics of fats and oils as well as the effectiveness of various agents, such as antioxidants, in improving those stability characteristics. This review of methods for stability and antioxidant measurement is intended to serve as a relatively brief outline of that particular area of fat and oil technology. Presented at the AOCS Short Course, “Processing Quality Control of Fats and Oils,” East Lansing, Mich., Aug. 29—Sept. 1, 1966.     

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.     

Copper in edible oils: Trace amounts determined by atomic absorption spectroscopy

The application of atomic absorption spectroscopy to trace copper analysis in fats was investigated. Copper spectral resonance lines 3248 A and 3274 A possess the most useful sensitivities applicable to fats and vegetable oils. These sensitivities were determined to be 0.15 and 0.25 ppm in oil, respectively, with detection limits about tenfold lower. Data show that copper absorption depends strictly on the amount of oil aspirated into the flame. In soybean oil-solvent mixtures, aspiration rates decrease logarithmically and linearly with increasing fat content. The accuracy and precision of atomic absorption techniques were established by comparing results from atomic absorption with those from two independent techniques. Error estimates were determined by analysis of copper-hydrogenated soybean oil diluted to low copper levels. The standard deviation, relative standard deviation and analytical error were 0.0108 ppm, 5% and 2.5%, respectively, over a range of 0.05–0.40 ppm copper in soybean oil. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970. Biometrical Services, ARS, USDA, stationed at Northern Laboratory. No. Market. Nutr. Res. Div., ARS, USDA.     

Ultraviolet spectrophotometric characteristics of unhydrogenated fish oils

Summary Typical ultraviolet spectrophotometric absorption curves are presented for unhydrogenated fish oils of commercial importance, before and after alkali isomerization. These curves show the usual maxima for isomerized polyunsaturated fatty acids, including five, and possibly six, double bonds. Tetraene absorption is sufficient to obliterate that of trienes completely. Such a method of analysis affords an easy means of detecting unhydrogenated fish oil contamination in the ordinary vegetable and animal oils and fats as well as a test for the presence of fish oils in admixture with raw linseed oil. Presented at 39th annual meeting of the American Oil Chemists' Society, New Orleans, La., May 4–6, 1948.     

Relative nutritional value of various dietary fats and oils

The dietary and nutritional role of fats and oils is quite complex, as evident in the new biological findings about some of their components that are essential to man. Fats and oils must be considered for both their quantitative and qualitative aspects, their fatty acid compositions and relationships with average diets in different countries should be emphasized. Because of some adverse physiological effects ascribed to saturated fatty acids, a tendency to increase the intake of polyunsaturated vegetable oils has occurred to provide a good source of essential fatty acids, mainly linoleic acid. However, saturated fats still are an important part of the diet in developed countries, especially “invisible” fats. Research must continue that is related to modifications fats and oils undergo during industrial processes which affect their nutritional value. Compositions of many fats and oils are provided.     

Fractionation of animal fat glycerides by crystallization from acetone. Am improved lard oil

Summary Various edible and inedible grades of animal fats, such as lard, grease, tallow, and selectively hydrogenated lard, grease and tallow were separated into “oils” and “stearins” by crystallization from acetone. The chemical and physical properties as well as the yields of oils and stearins obtained by this method are described. Antioxidants and metal deactivators are much more effective in stabilizing lard and grease oils produced from partially hydrogenated fats than in stabilizing corresponding products from unhydrogenated fats. Report of a study certain phases of which were made under the Research and Marketing Act of 1946. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.     

The fluorescence of chlorophyll in fats in relation to rancidity

Summary 1.) Difficulties in applying the “chlorophyll value” test to fat samples has led us to investigate the apparent “quenching” of chlorophyll fluorescence in mineral oil solution when cottonseed oil or lard is added to it. The disappearance of chlorophyll fluorescence in ultraviolet light caused by the addition of cottonseed oil appears to be due to the absorption of the light by the cottonseed oil and to the intense white fluorescence of the oil itself rather than to a chemical reaction of some constituent of the oil with the excited chlorophyll. 2.) There was no evidence of a stoichiometric quenching reaction between chlorophyll and acceptor substances in the fats used in this study and, in consequence, no “endpoint” was observed in any of the titrations. 3.) A lack of correlation between either the peroxide value or the stabilities measured in conventional ways and the amount of chlorophyll fluorescence of several fats makes the “chlorophyll value” test appear to have doubtful value as a generally applicable test for fat rancidity or stability. 4.) The crude absorption curves here presented suggest that the greater absorption of near ultraviolet light by oxidized fats may be related to their content of fat peroxides. This work was made possible by grants from the Rockefeller Foundation, the Hormel Foundation, and the Graduate School of the University of Minnesota. Assistance in the preparation of these materials was furnished by the personnel of Work Projects Administration, Official Project No. 165-1-71-440, Subproject No. 382.     

Monitoring the oxidation of edible oils by Fourier transform infrared spectroscopy

Edible fats and oils in their neat form are ideal candidates for Fourier transform infrared (FTIR) analysis, in either the attenuated total reflectance or the transmission mode. FTIR spectroscopy provides a simple and rapid means of following complex changes that take place as lipids oxidize. Safflower and cottonseed oils were oxidized under various conditions, and their spectral changes were recorded and interpreted. The critical absorption bands associated with common oxidation end products were identified by relating them to those of spectroscopically representative reference compounds. The power and utilty of FTIR spectroscopy to follow oxidative changes was demonstrated through the use of “real-time oxidation plots.” A quantitative approach is proposed in which standards are used that are spectroscopically representative of oxidative end products and by which the oxidative state of an oil can be defined in terms of percent hydroperoxides, percent alcohols and total carbonyl content. By using either relative absorption as a basis or calibrating on representative standards, FTIR analysis provides a rapid means of evaluating the oxidative state of an oil or of monitoring changes in oils undergoing thermal stress.     

The role of the northern regional research center in the development of quality control procedures for fats and oils

The research laboratory has played a major role in the development of quality control procedures for edible fats and oils. Historically, development of these methods can be traced in part to the need for basic information on the composition, processing and flavor stability of edible soybean oil. The Northern Regional Research Center pioneered much of this basic work. This review will address the contributions made by the Northern Center in developing quality control procedures for edible fats and oils. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned. Presented at the 73rd AOCS annual meeting, Toronto, 1982, as part of the symposium on Quality Control in Fats, Oils and Oilseeds.     

A rapid method for the quantification of fatty acids in fats and oils with emphasis on <Emphasis Type="Italic">trans</Emphasis> fatty acids using fourier transform near infrared spectroscopy (FT-NIR)

A rapid method was developed for classifying and quantifying the FA composition of edible oils and fats using Fourier Transform near infrared spectroscopy (FT-NIR). The FT-NIR spectra showed unique fingerprints for saturated FA, cis and trans monounsaturated FA, and all n−6 and n−3 PUFA within TAG to permit qualitative and quantitative comparisons of fats and oils. The quantitative models were based on incorporating accurate GC data of the different fats and oils and FT-NIR spectral information into the calibration model using chemometric analysis. FT-NIR classification models were developed based on chemometric analyses of 55 fats, oils, and fat/oil mixtures that were used in the identification of similar materials. This database was used to prepare three calibration models—one suitable for the analysis of common fats and oils with low levels of trans FA, and the other two for fats and oils with intermediate and high levels of trans FA. The FT-NIR method showed great potential to provide the complete FA composition of unknown fats and oils in minutes. Compared with the official GC method, the FT-NIR method analyzed fats and oils directly in their neat form and required no derivatization of the fats to volatile FAME, followed by time-consuming GC separations and analyses. The FT-NIR method also compared well with the official FTIR method using an attenuated total reflectance (ATR) cell; the latter provided only quantification of specific functional groups, such as the total trans FA content, whereas FT-NIR provided the complete FA profile. The FT-NIR method has the potential to be used for rapid screening and/or monitoring of fat products, trans FA determinations for regulatory labeling purposes, and detection of contaminants. The quantitative FT-NIR results for various edible oils and fats and their mixtures are presented based on the FT-NIR model developed.     

Refining and degumming systems for edible fats and oils

Crude edible fats and oils contain variable amounts of nonglyceride impurities, such as free fatty acids, non-fatty materials generally classified as “gums”, and color pigments. Most of these impurities are detrimental to end product fresh and aged quality characteristics, hence must be eliminated by a purification process before the finished fats and oils are suitable for human consumption. The object of this process is to remove these objectionable impurities with the least possible loss of neutral oil and tocopherals. Key theoretical and practical factors for degumming and refining crude edible oils are discussed with particular reference to processes, flow charts, control systems and analytical testing requirements. In addition to typical large volume oils, such as soya and cotton, techniques are also reviewed for smaller volume oils, including palm, lauric and corm.     

The structure and chemical composition of fats and oils

This is essentially a general review of progress during the past ten years both in the chemistry of the glycerides of fats and oils and in the chemistry and nature of their constituent fatty acids. Applications of some of the newer research methods are described and discussed. This paper was presented at the Symposium on the Chemistry & Metabolism of Fats, held at the Rochester meeting of the American Chemical Society. It is published here by special arrangement with the Division of Agricultural & Food Chemistry.     

Application of ultraviolet spectrophotometry to the analysis of fats and derivatives

Summary There are several spectrophotometric methods available which allow a high degree of accuracy in the analysis of the common fats and oils. Further there are methods available for those fats and oils that contain unsaturated acids up to and including hexaenoic acid which allow good estimations of the composition. Several sources of error are discussed in an effort to point the way to their elimination. Recently published spectrophotometric data on certain polyunsaturated acids isolated from marine oils are discussed in relation to the possibility of extending the method to include these oils. More accurate spectrophotometric constants to be employed in the analysis of certain drying oils are suggested. Presented at the American Oil Chemists' Society, Minneapolis, Minn., October 11–13, 1954. A laboratory of the Eastern Utilization Research Branch, Agricultural Research Service, United States Department of Agriculture.     

Quantitative spectroscopy to determine the effects of photodegradation on a model polyester-urethane coating

During the accelerated exposure of a model polyester-urethane coating, measurements were taken at intervals to determine how the ultraviolet absorption, erosion, and chemical change proceeded during degradation. Infrared spectra showed that the carbonyl concentration increased with exposure as the material oxidized, but the ultraviolet results showed carbonyl peaks that diminished with exposure. Changes in optical path length, carbonyl concentration (both infrared and ultraviolet), and C–H concentration appeared linear with the exposure period. Knowing the chemical composition of the polyester and its reaction with isocyanurate made it possible to construct a representative model of the polymer network. Computational chemistry provided confirmation of the literature on which elements of the network were susceptible to degradation. As the polymer eroded, the aromatic content including some carbonyl was lost, but the remaining polymer was oxidized. Quantitative estimates were made for the mass lost and the change in concentration of the carbonyl and CH concentrations that agreed well with results from both the infrared and ultraviolet spectroscopy. Knowing the polymer composition allowed thickness change, a macroscopic quantity, to be connected to chemical changes via the polymer network model. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, in New Orleans, LA. Dept of Polymers and Coatings, 1735 NDSU Research Park Dr., P.O. Box 5376, Fargo. ND 58105-5376.     

Sampling improvements in atomic absorption spectroscopy

Atomic absorption spectroscopy is being used as a routein method to determine sodium, potassium, calcium, magnesium, copper and many other metallic elements in oils, fats, milk and other substances. Copper and iron can be measured directly in milk without sample preparation. When highly acidified samples are run, a new plastic-lined nebulizer is useful to prevent spurious results due to corrosion. A new sampling device, the Graphite Furnace, can analyze extremely small samples and gives detection limits in the picogram (10⁻¹² g) range. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970.     

A method for the determination of linoleic acid and conjugated dienoic acids in materials containing eleostearic acids

Summary A procedure has been described which extends the scope of the spectrophotometric method for polyun-saturated acids to the determination of linoleic and conjugated acids in the presence of large quantities of conjugated trienoic acids. Basis for the proposed method rests on equations which are offered to correct the “end” or “back-ground” absorption of the highly absorbing triene conjugated acids at 233 mμ, the position of maximum absorption of conjugated dienoic acids and alkali isomerized linoleic acids. The method is limited to samples which do not contain nonconjugated trienoic acids (linolenic acids). The method has been tested by the analysis of several mixtures of cottonseed and dehydrated castor oils of known composition, to which varying amounts of alpha, beta, and mixtures of alpha- and beta-eleostearic acids have been added. These samples have been used to demonstrate the application of the proposed method for the determination of dienoic conjugated acids, alpha-eleostearic acid, beta-eleostearic acid linoleic acid, oleic acid, and total saturated fatty acids. Comparisons of the results obtained with similar values, calculated from the known composition of the mixtures, prove that the proposed method gives reasonable results. Standard deviations between determined and calculated results vary from 0.36 for diene conjugated acids to 1.40 for oleic acid. The method has been applied to the analysis of foreign and domestic tung oils. Presented before the American Oil Chemists' Society, Cincinnati, O., Oct. 20–22, 1952. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Confectionery fats from palm oil and lauric oil

In the search for economical cocoa butter alternatives, palm and lauric oils have emerged as important source oils in the development of hard butters. Based on the method presented for categorizing hard butters, the lauric oils, primarily palm kernel and coconut, can be modified by interesterification and hydrogenated to yield lauric cocoa butter substitutes (CBS) which are both good eating and inexpensive. Fractionation, although adding to the cost of production, can provide lauric hard butter with eating qualities virtually identical to cocoa butter. Unfortunately, one factor identified with the lauric oils is their very low tolerance for cocoa butter. Palm oil, on the other hand, has been identified as a valuable component in all types of cocoa butter alternatives. It is a source of symmetrical triglycerides vital in the formulation of a cocoa butter equivalent (CBE). It can be hydrogenated or hydrogenated and fractionated to yield hard butters with a limited degree of compatibility with cocoa butter, allowing some chocolate liquor to be included in a coating for flavor enhancement. Palm oil is used with lauric oils as a minor component in interesterified lauric hard butters, as well as functioning as a crystal promoter in coatings formulated with a fractionated lauric CBS. While palm oil’s importance and flexibility have been duly noted, some important concerns remain from a market perspective. The fact that the CBE fats are very expensive suggests they offer limited cost savings compared to cocoa butter. The potential for CBE products is still questionable in those countries where chocolate labeling standards preclude the use of vegetable fats other than cocoa butter. The nonlauric CBS products, while cheaper than the CBE types and able to tolerate limited levels of cocoa butter, do not exhibit the level of eating quality characteristics present in the lauric hard butters. Some challenges remain for today’s oil chemists. An economical nonlauric CBS, made predominantly from palm oil, possessing the eating quality of a fractionated lauric CBS and exhibiting good compatibility with cocoa butter would be met with considerable interest by the chocolate and confectionery industries. As for the lauric oils, it would seem reasonable to assume that greater cocoa butter compatibility, if attainable, could enhance their potential for gaining even greater acceptance by confectionery manufacturers currently using pure chocolate. As for the CBE products, the major issue is cost. If the cost of a CBE could be reduced to a level which would allow a CBE to compete with the nonlauric and lauric cocoa butter substitutes, a major advancement in the evolution of cocoa butter alternative fats will have been achieved.     

Applied ultraviolet spectrophotometry of fats and oils

Conclusion The chemist has in the spectrophotometric method a rapid and simple means of studying changes in the double bond systems of fatty acids. The method is highly sensitive. It has found application in studies of processing of oils, improvement of drying oils, catalytic hydrogenation, routine analytical work, soap and tallow control, as well as in nutrition studies in which the composition of depot and ingested fats are of interest. It also finds application in strictly academic studies which have as their purpose an extension of our knowledge concerning the composition of naturally occurring fats and oils. In general, it is especially valuable in cases in which thiocyanometric procedures are not sufficiently sensitive or in which conjugated as well as non-conjugated constituents occur. Presented at the 19th annual fall meeting of the American Oil Chemists' Society, Nov. 7–9, 1945, in Chicago