Rapid determination of free fatty acids in vegetable oils by gas liquid chromatography

Determination of the free fatty acids in small quantities of vegetable oil is accomplished by gas liquid chromatography. The free fatty acids are isolated from a hexane solution of the vegetable oil into an aqueous solution of trimethylphenylammonium hydroxide (TMPH). Due to the alkalinity of TMPH, the free fatty acids readily partition into this aqueous phase. Injection of the free fatty acid-TMPH salts into a gas chromatograph results in pyrolytic methylation of the free fatty acid salts—yielding the methyl esters. Excellent results were obtained when this new procedure was used on neutral lipid oils containing known amounts of free fatty acids and compared with the results obtained by a modified BF₃/MeOH esterification procedure. When compared to the AOCS titration procedure, this new procedure gave comparable results. This new procedure has advantages over the AOCS procedure: it is more sensitive and gives quantitative results for individual free fatty acids. This new procedure also has several advantages over the modified BF₃/MeOH esterification procedure: it is easily and more rapidly performed, there is no deposition of glyceride on the column when the sample is injected, and because there is quantitative recovery, the new procedure is more sensitive and can be used on oils with a low weight percentage of free fatty acids.     

Quantitative determination of glycerol,mono- and diglycerides by gas liquid chromatography

Standard chemical procedures for the determination of glycerol, mono- and diglycerides in food products are lengthy, particularly when more than one component has to be determined in the same sample. Gaschromatographic techniques are applicable to these compounds when they are converted into their trimethylsilyl derivatives. A simple, rapid and quantitative gas chromatographic procedure has now been developed which is based on the addition of an internal standard (cholesteryl acetate) to samples which are subsequently silylated. This procedure has been applied to the direct determination of glycerol, mono- and diglycerides in emulsifiers, shortenings and other samples. Presented at the AOCS Spring Meeting, San Francisco, California, April 1969.     

Compositional characterization of cottonseed soapstocks

Cottonseed soapstock samples, collected during the 1993–1994 crushing season from oilseed extraction mills throughout the United States Cotton Belt, were analyzed by chemical and chromatographic methods. Volatiles averaged 48.7±10.6% (mean±SD,n=39). On a dry basis, the samples averaged 33.3±7.3% fatty acids, 26.3±6.9% phospholipids, 8.4±6.4% triglycerides, and 7.5±3.0% gossypol. The analytical techniques accounted for 93.3±8.6% of the dry soapstock matter. The AOCS method for total fatty acids in soapstock yielded values in agreement with the chromatographic and phosphorus analyses. In contrast, the AOCS method for neutral oil in soapstock gave values that were significantly higher than those obtained by chromatography. The amount of nonlipid material in the samples correlated with the phosphorus content. Total gossypol and nitrogen levels were also related.     

Calculation of iodine value from measurements of fatty acid methyl esters of some oils: Comparison with the relevant American Oil Chemists Society method

A new calculation method for the determination of iodine value (IV) from measurements of fatty acid methyl esters is proposed. The method is based on the quantitative determination of fatty acid methyl esters of vegetable oils by capillary gas chromatography. IV is a measure of the number of double bonds in the unsaturated fatty acids in one gram of oil. The analytical methodology of its evaluation includes the use of rather health dangerous reagents, and for that reason is mostly avoided by laboratory analysts. A calculation procedure to determine the IV of oils from their fatty acid methyl ester composition is in use based on the American Oil Chemists’ Society (AOCS) method Cd 1c-85. A new calculation procedure for IV, based also on the evaluation of the fatty acid methyl esters of oils, was developed. The application of the proposed calculation methodology was checked with olive oil, corn oil, soybean oil, cottonseed oil, and sunflower seed oil. The proposed calculation gave results in better agreement with the Wijs method than with the relevant AOCS method.     

A comparison of the cup refining loss and neutral oil determinations for evaluating crude soybean oil

Data from 833 non-degummed and degummed soybean oil samples, which were analyzed by both the neutral oil loss and cup loss methods, were examined, and it was found that the total premiums paid under the cup loss method and the proposed National Soybean Processors Association Technical Committee’s neutral oil analysis were the same. However, better quality oils would have received a higher premium, while poorer oils would have been penalized more heavily under the new procedure. Presented at the AOCS meeting in Toronto, Canada, 1962.     

Determination of phosphorus in oils using oxygen bomb ashing

A fast method for phosphorus determination in an oil matrix is described. The principle of the method is similar to that of the AOCS method, but the ashing of the oil is accelerated using an oxygen bomb. In addition, a rapid molybdovanadate reagent is used for colorimetry rather than the molybdenum blue reagents specified in the AOCS method. Agreement with the air ashing procedure averages less than 5% difference above 10 μg/g. The detection limit is in the order of 1~2 μg/g.     

A modified VERI-FRY® quick test for measuring total polar compounds in deep-frying oils

The AOCS official method for the determination of total polar compounds in deep-frying oils is often used to estimate frying oil degradation. It can be accurate and reliable, but with sacrifices of time and expense. The TPM VERI-FRY® PRO (Libra Technologies, Inc., Metuchen, NJ) quick test provides a quick and easy way to measure polar compounds in frying oils. The modified quick test measured at 490 nm has a good correlation with the AOCS official method (r=0.975, P<0.001) and provides a good estimate of polar compound accumulation in oils over 80 h of deep-frying. Using the quick test to measure polar compounds is fast, convenient, economical and reliable.     

New FTIR method for the determination of FFA in oils

A rapid, practical, and accurate FTIR method for the determination of FFA in edible oils was developed. Analogous to the AOCS titration procedure, the FTIR FFA determination is effected by an acid/base reaction but directly measures the product formed rather than utilizing an end point based on an electrode potential or color change. A suspension of a weak base, potassium phthalimide (K-phthal) in 1-propanol (1-PrOH), is used to convert the FFA present in oils to their carboxylate salt without causing oil saponification, and differential spectroscopy is used to circumvent matrix effects. Samples are first diluted with 1-PrOH, then split, with one-half treated with the K-phthal reagent and the other half with 1-PrOH (blank reagent), their spectra collected, and differential spectra obtained to ratio out the invariant spectral contributions from the oil sample. Quantification of the percentage of FFA in the oil, expressed as %oleic acid, based on measurement of the peak height of the ν (COO⁻) absorption of the FFA salt formed, yielded a calibration with an SE of <0.020% FFA over the range of 0–4%. The method was validated by standard addition and the analysis of Smalley check samples, the results indicating that the analytical performance of the FTIR procedure is as good as or better than that of the standard titrimetric procedure. As structured, the FTIR procedure is a primary method, as calibration is not dependent on reference values provided by another method, and has performance criteria that could lead to its consideration as an instrumental AOCS procedure for FFA determination. The FTIR portion of the analysis is automatable, and a system capable of analyzing ∼60 samples/h was developed that could be of benefit to laboratories that carry out a large number of FFA analyses per day.     

A quality control procedure for the gas liquid chromatographic evaluation of the flavor quality of vegetable oils

An objective procedure which is relatively simple and rapid is under study for the determination of the flavor quality of vegetable oils. This procedure utilizes the direct injection of an oil sample to which has been added an internal standard, into a packed precolumn of a gas Chromatograph. The volatiles are swept from the precolumn through a 10% SE-30 column under operating parameters which permit complete elution of all volatiles and internal standard within 20 min. Some 1 5 to 20 samples can be evaluated in one day before it is necessary to replace any part of the foot-long precolumn. Evaluations have been made by the gas liquid Chromatographic (GLC) procedure and by a flavor panel of oil samples subjected to a variety of storage conditions. Generally, differences in the GLC pattern are reflected in the flavor panel results. ted at the AOCS Meeting, New Orleans, April 1976.     

Dry column method for the quantitative extraction and simultaneous class separation of lipids from muscle tissue

A method for lipid isolation is presented that is alternative to the traditional chloroform/methanol extraction methods. This new method allows lipid isolation by solvent elution of a dry column composed of a tissue sample, anhydrous sodium sulfate, and Celite 545 diatomaceous earth groud together. To isolate total lipids, the dry column is eluted with a mixture of dichloromethane/methanol (90∶10, v/v). Alternatively, the lipids may be isolated and simultaneously separated into neutral and polar fractions by a sequential elution procedure; neutral lipids free of polar lipids are eluted first with dichloromethane, followed by elution of polar lipids with the dichloromethane/methanol (90∶10) mixture. The two dry column methods-isocratic or sequential elution-were compared with the traditional chloroform/methanol methods by gravimetric, thin layer chromatographic and phosphorus analyses. Presented in part at the AOCS 70th Annual Meeting, San Francisco, May 1979. Agricultural Research, Science and Education Administration, U.S. Department of Agriculture.     

Determination of chlorophyll pigments in crude and degummed canola oils by HPLC and spectrophotometry

Chlorophyll pigments in crude and degummed canola oils were analyzed by spectrophotometry using a modified AOCS Method and by reversed phase HPLC. HPLC showed that crude canola oils contained very littlechlorophyll a orb, these pigments having been converted to pheophytins and other pigments with similar spectral properties. The ratio ofchlorophyll a∶b in the seed was found to be about 3∶1 while the ratio ofpheophytin a∶b in the oil was about 9∶1. As the AOCS Method for determining oil chlorophyll was calibrated for pure chlorophyll, the use of this method on crude canola oil results in a significant error. Recalibration of the spectrophotometric procedure with pheophytin gave better agreement with the HPLC method. Paper No. 635 of the Canadian Grain Commission, Grain Research Laboratory, 1404-303 Main Street, Winnipeg., Manitoba, Canada R3C 3G8. Presented at the A.O.C.S. 79th Annual Meeting, Phoenix.     

Absolute neutral oil content of vegetable oils by radiochemical technique

Laboratory refining loss, determined by the chromatographic method, is checked by a radio-chemical procedure. Neutral triglycerides are labeled with C¹⁴-tripalmitate and passed through an alumina column to find out if the alumina retains a percentage of them. Cottonseed oil is also labeled and, by applying the calculations of the isotope dilution analysis, the absolute neutral oil content and therefore the theoretical refining loss are determined. The theoretical and the chromatographic refining losses are compared, and a relation between them is proposed for cottonseed oils.     

Catalysts for selective hydrogenation of soybean oil. I. An experimental method for evaluating selectivity

The undesirable flavor reversion properties of soybean oils may be counteracted by selective hydrogenation of the linolenate components. Screening of catalysts for this purpose was accomplished by a standardized laboratory hydrogenation of a refined, bleached soybean oil under atmospheric pressure. A mathematical derivation utilizes analytical chromatographic data to determine linolenate/linoleate reaction rates as a selectivity index S_L for a given catalyst. Presented at the AOCS Meeting, Toronto, 1962.     

A modified method for determining free fatty acids from small soybean oil sample sizes

A modification of the AOCS Official Method Ca 5a-40 for determination of free fatty acids (FFA) in 0.3 to 6.0-g samples of refined and crude soybean oil is described. The modified method uses only about 10% of the weight of oil sample, alcohol volume, and alkali strength recommended in the Official Method. Standard solutions of refined and crude soybean oil with FFA concentrations between 0.01 and 75% were prepared by adding known weights of oleic acid. The FFA concentrations, determined from small sample sizes with the modified method, were compared with FFA percentages determined from larger sample sizes with the Official Method. Relationships among determinations obtained by the modified and official methods, for both refined and crude oils, were described by linear functions. The relationship for refined soybean oil had an R ² value of 0.997 and a slope of 0.99±0.031. The values for crude soybean oil are defined by a line with R ²=0.9996 and a slope of 1.01±0.013.     

Chromatographic determination of neutrals in tall oil fatty acids,gum and wood rosin

A simple analytical method for the determina-tion of the neutrals (nonacidics) in tall oil fatty acids, gum and wood rosin has been developed. The method is based on the use of Chromatogra-phic techniques for the separation of the acidic from the nonacidic fraction by using alumina as the adsorbent and acetone as the solvent. Data are presented which show good agreement between a calculated theoretical nonacidic content and the amount actually found by the chromatographie procedure as well as the standard AOCS procedure for unsaponifiables. To correct for any acidity in the sample that might have been eluted from the column, dissolve the residue in 50 ml of neutral 2:1 benzene-methyl alcohol and titrate to a thymol blue end-point with approximately 0.1 normal alcoholic KOH. This value is usually zero unless the column is overloaded.     

Investigation of methods for determining the refining efficiency of crude oils

Conclusions Various methods for estimating the neutral oil content, or conversely the loss constituents of crude cottonseed oil and soybean oil, have been explored. Of those techniques studied the International Chemical Union chromatographic procedure seemed most appropriate because it was found to be reasonably accurate and most reproducible, was easy and rapid to carry out, and required no special, elaborate, or expensive equipment. The chromatographic method has been successfully applied to a variety of crude cottonseed and soybean oils and to a few vegetable oil residues containing high percentages of loss constituents. The results obtained with this technique would appear to be eminently suitable for evaluating the efficiency of plant refining processes. Indications are that the method might ultimately prove useful for establishing the value of the various lots of crude cottonseed oil and soybean oil which normally change hands in commercial channels. The last-mentioned application will probably have to wait for the development of a suitable companion, semimicro, or chromatographic bleach test and the adoption of an adequate acceptable standard spectrophotometric method for measuring oil color. Presented at annual fall meeting, American Oil Chemists' Society, Chicago, Oct. 31-Nov. 2, 1949     

Factors affecting slip melting point of palm oil products

The effect of different factors affecting the slip melting point of palm oil has been evaluated. The most important factor appears to be the difference in tempering temperatures. The influence of different tempering temperatures on slip point values is, however, dependent on the nature of the sample. For hydrogenated oils and for some high-melting palm stearins, tempering has no effect. For palm oil and palm olein, higher melting points were obtained when tempering at the higher temperatures in the range of 4–15 C. For some soft stearins, however, lower melting points were obtained at the higher tempering temperatures. These effects are investigated with differential scanning calorimetry and an explanation is offered, based on phase diagrams. A secondary effect on the slip melting point was the height of fat in the capillary tube. Effects of using different methods of determination are also shown. Collaborative trials on a standard testing procedure, AOCS Cc3-25, revealed the inadequacy for palm oil of the temperature range of 4–10 C specified in the procedure and its fractions. Strict adherence to a fixed tempering temperature produced better precision and reproducibility among laboratories. Tempering at 10±1 C is recommended.     

毛细管气相色谱法测定洗油中萘含量

洗油萘含量是洗油的主要质量指标,洗油萘含量的测定方法国际标准规定有2种:一是采用蒸馏结晶点法,该法准确度和精密度都较差;二是采用GB/T 24208-2009规定的色谱法,该法虽然采用先进的色谱技术代替结晶点法,但在色谱柱的选择和定量方法的选择方面仍有改进余地。采用毛细管色谱法分析测定洗油中的萘含量。该法分析时间短,操作简单,准确度和精密度都较高,完全可取代以上2种方法。整个试样分析时间只有15min,可直接用于产品质量分析与控制,为现场分析和操作调节提供了便捷。     

Aqueous extraction—An alternative oilseed milling process

Oil can be removed from oilseed materials by a process which consists of an aqueous extraction of the comminuted seed, followed by a centrifugal separation which divides the aqueous extract into oil, solid, and aqueous phases. The protein may be recovered in the solids or aqueous phase, depending upon the conditions selected. Unit operations of this process are grinding, solid-liquid separation, centrifugation, demulsification, and drying of products. Aqueous extraction has been applied, to date, to coconuts and peanuts. For coconuts, a procedure has been developed to recover 93% of the oil and 91% of the protein. The major protein product is 25% protein and, when reconstituted in water, forms an acceptable beverage. The estimated production cost of this product is $.24/1b. For peanuts, the recovery of oil was 89% and protein 92% for the concentrate procedure, whereas the corresponding values for the isolate procedure were 86% and 89%, respectively. The costs of production were estimated as $.17/1b of concentrate (67% protein) and $.28/1b of isolate (89% protein). Aqueous extraction offers several advantages over conventional solvent extraction-less initial capital investments, safer operation, capability of discontinuous operation, and production of a variety of products. Another advantage of aqueous processing is the capability for utilization of certain chemicals to remove or inactivate undesirable substances. In the case of peanuts, hydrogen peroxide and sodium hypoehlorite have proven to be effective for destruetion of aflatoxins. Aqueous processing has the potential for application to a variety of other oilseeds. One of seven papers presented at the symposium, “Processing Methods for Oilseeds,” AOCS Spring Meeting, April 1973.     

Comparative study of methods of determining oil content of sunflower seed

An extraction-gravimetric method (AOCS Official Method Ai 3-75) was compared with 2 instrumental techniques, near-infrared reflec-tance (NIR) spectroscopy and wide-line nuclear magnetic resonance (NMR), for the determination of the oil content of oilseed-type hybrid sunflower seed. Eight sunflower seed samples of varying oil contents, replicated 5 times, were analyzed by the 3 procedures. The overall mean oil contents and standard deviations for the 8 samples were: AOCS method, 44.5% ± 0.33%; NMR, 44.8% ± 0.27%; and NIR, 44.2% ± 0.81%. Analysis of variance of the means of the 3 methods of analysis indicated no difference (p>0.05) in oil content due to the method. However, there was a difference (p>0.001) in total oil content due to replicated analyses of the same sample with the NIR method. With the AOCS and NMR methods, no effect (p>0.05) of replicated analyses of the same sample was found. The NMR method was more precise and repro-ducible than the other 2 methods. Although the NIR mean oil contents were not significantly different from the means of the other 2 methods, the coefficient of variations for all samples were consistently higher for the NIR analyses than for the AOCS and NMR analyses.