Concerns for the determination of free fatty acid in cottonseed

The official AOCS method for the determination of free fatty acid (FFA) in cottonseed requires dehulling the seed, grinding the meats with a 12-blade food processor, and extracting the ground meats in a butt tube with three portions of room-temperature petroleum ether. The extracted oil, after desolventization, is then titrated with NaOH to the end point of phenolphthalein in a mixed solvent of isopropanol and hexane. Our study showed that this procedure tends to underestimate the amount of FFA present in the oil of cottonseed by as much as 11.5%. It was also found that to obtain consistent and accurate FFA content, a desirable particle size is smaller than 10 mesh (preferably <14 mesh), minimum extraction temperature should be no less than 40°C (preferably greater than 50°C), and the extraction time should be longer than 2 h in a Soxhlet extractor.     

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.     

Evaluation of chromatographic separation of free lutein and fatty acids in de-esterified marigold lutein

In this study, chromatographic purification of de-esterified marigold lutein was evaluated to obtain high purity free lutein. The quantification and identification of fatty acid in the de-esterified marigold lutein, which have not been reported before, were determined. The amount of fatty acid, mostly palmitic acid, was 49.12 mg/g oleoresin. The separation of free lutein and fatty acid was then performed. The high purity and recovery of free lutein were observed to be 99.2% and 95.2%, respectively, for the suitable chromatographic separation condition, i.e., step-gradient of hexane-ethyl acetate mixture at 85:15 v/v in the first 12 min, followed by 70:30 v/v.     

Solid‐phase extraction in combination with GC/MS for the quantification of free fatty acids in adipocere

Current research investigating the effect of specific aquatic microenvironments on the formation of adipocere using domesticated pigs (Sus scrofa) has demonstrated the need for a fast and reliable method to separate and identify fatty acids present in adipocere. Adipocere is defined as a late‐stage post‐mortem decomposition product consisting of a mixture of free fatty acids (FFA), which have formed under favorable conditions due to the hydrolysis of triglycerides in adipose tissue. Whilst good separations of adipocere lipids have been achieved using TLC, this method is time consuming when processing large numbers of samples. This paper describes a rapid and simple method for the extraction, identification and quantification of FFA commonly found in adipocere, by solid‐phase extraction (SPE) using aminopropyl disposable columns in combination with GC/MS. The recoveries of FFA associated with adipocere were all above 90%, with coefficients of variation below 10%, indicating that the technique was reproducible. The limits of quantification were registered at levels of parts per million. Standard curves were linear over the range of 50–1000 µg/mL, with all correlation coefficient values greater than 0.998. A marked increase in concentration of saturated fatty acids was observed during adipocere formation, ranging from 20 to 55% for palmitic acid, 13 to 23% for stearic acid and 2.8 to 4.1% for myristic acid. These results demonstrate the suitability of aminopropyl disposable SPE columns to efficiently and rapidly isolate FFA from adipocere prior to quantitative GC/MS analysis.     

The liberation of free fatty acids in potato slices at low temperature

Free fatty acids (FFA) are liberated in the first stages of potato granule production. In this study, the liberation of FFA was examined in model experiments. Potato slices were exposed to conditions resembling the first stages of the industrial process, which was of the “add-back type”. The slices were kept at 9°C in the dark and, after various periods of time (up to two hours), the amount and composition of the FFA liberated at the surface and in the middle of the potato slices were analyzed by gas chromatography. The liberation of FFA was more pronounced at the surface of the slices than in the middle. The polyunsaturated fatty acids, linoleic acid and linolenic acid, were liberated to a greater extent than the saturated fatty acids. The experiment was repeated at 4°C and the results obtained were very similar. The lower temperature did not decrease the rate of FFA liberation. But, in thin potato strips, which have a larger total surface of damaged membranes than the potato slices, considerably more FFA were liberated. The amount and composition of FFA also were analyzed in potato slices from the industrial process for potato granule production. Before the blanching bath (76°C for 12–15 min) only minor amounts of FFA were liberated but during the blanching there was a substantial liberation of FFA at the surface of the potato slices. After the blanching bath there were no more FFA liberated at the surface of the slices but in the middle of the potato slices the liberation of FFA continued until the potato slices reached the steamcooking bath.     

Recovery of fatty acids by immobilized solvent extraction

The use of silicone rubber tubes swollen with solutions of TOPO (trioctyl phosphine oxide) in kerosene as membranes for the recovery of fatty acids from anaerobic digesters was investigated. The flux of acetic and propionic acids was found to increase with the concentration of TOPO when the concentration was low. At very high TOPO concentrations, the flux decreased indicating the existence of an optimum TOPO concentration. The relationship between the flux and concentration of unionized propionic acid did not agree with that expected for pure diffusion. This was due to the reversible reaction between TOPO and propionic acid in the membrane. The flux of propionic acid was measured as a function of time for new membranes and for membranes removed from storage. Rather long times, 70 to 300 hours, were required to achieve steady acid fluxes. This time was required to fully develop the concentration profiles within the membranes.     

Comparison between extraction of lipids and fatty acids from microalgal biomass

Seven solvent mixtures have been used to extract the lipid fraction of lyophilized biomass ofIsochrysis galbana. Six of them were composed of biocompatible solvents. Each method was carried out under relaxed operating conditions (i.e., one hour at room temperature) with extraction in a nitrogen atmosphere to prevent autooxidation and degradation of polyunsaturated fatty acids (PUFAs). Apart from the well-established Bligh and Dyer method [Can. J. Biochem. Physiol. 37:911 (1959)] (Cl₃CH/MeOH/H₂O, 1∶2∶0.8, vol/vol/vol), which rendered the highest yield of lipids (93.8%), ethanol (96%) and hexane/ethanol (96%), 1∶2.5 vol/vol produced the best results (84.4 and 79.6%, respectively). To obtain free fatty acids, KOH was added to the solvent mixtures used to extract the total lipids, except for Cl₃CH/MeOH/H₂O, and direct saponification was carried out at 60°C for 1 h or at room temperature for 8 h. The highest yields obtained by direct saponicification were 81% with hexane/ethanol (96%), 1∶2.5, vol/vol and 79.8% with ethanol (96%). Partial yields of the mainn-3 PUFAs found inI. galbana, stearidonic acid (SA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were calculated for both extraction methods. For lipid extraction with ethanol (96%), yields of 91, 82 and 83% were obtained for SA, EPA and DHA, respectively. When direct saponification was used, hexane/ethanol (96%; 1∶2.5, vol/vol) produced the best yields of (91, 79 and 69% for SA, EPA and DHA, respectively).     

双液相萃取棉籽油制备脂肪酸甲酯

以双液相萃取技术处理棉籽,在得到脱毒棉粕的同时得到含有高质量毛油的非极性相。以非极性相作为与甲醇进行酯交换反应的原料,得到脂肪酸甲酯和甘油。考察了非极性相溶剂石油醚与棉籽油的比例对酯交换转化率和洗涤粗产品用水量的影响,确定了石油醚与棉籽油的最佳质量比为3,在此条件下,洗涤用水量可降低一半。考察了醇油比、催化剂用量、反应温度、反应时间等参数对转化率的影响。应用正交实验的方法找出酯交换反应的适宜条件为：醇油比6：1,催化剂用量1.1％,反应温度60℃,反应时间120min。在此反应条件下,产物中脂肪酸甲酯的含量可达97.4％。     

Alternative extraction effects on the free fatty acids and phosph in oil from damaged and undamaged soybeans

By varying the extracting conditions, it may be possible to produce high-quality, low-phosphorus and low-free fatty acid (FFA) oil extracted from water or mechanically damaged soybeans. The variability in phospholipids and FFA was studied in oil extracted by an alternative process from undamaged, damaged and aged soybeans subjected to various changes. Forrest and Hutcheson cultivars were used, and extractions were from finely ground flour rather than from flakes. Freezing caused the maximum increase in FFA and phosphorus levels compared to other levels in damaged or undamaged soybeans, but the levels were reasonable compared to flake extraction. Phosphorus and FFA increased when storage temperatures went from 25 to 45°C, extraction temperatures from 25 to 50°C and moisture of the flour from 6 to 10%. However, the storage time of soybeans with initially high moisture (20%) did not have a marked influence on FFA and phosphorus levels. Immediately after grinding moisture of the flour elevated or lowered the phosphorus level to a great extent, although it had little influence on the FFA level. Phosphatidic acid and phosphatidylcholine were identified as the main phospholipids present when total phosphorus was low in extracted oil. The time taken for the flour to dry to 6% moisture (after grinding and before it was extracted) was critical. The alternative extraction process moderated the expected increase in FFA and phospholipids as the result of soybean damage.     

Kinetic studies on the esterification of free fatty acids in jatropha oil

Kinetic studies have been carried out on the esterification of free fatty acids (FFAs) in jatropha oil with methanol in the presence of sulphuric acid catalyst at 5 and 10 wt% concentrations relative to free fatty acids (0.4–0.8 wt% relative to oil) and methanol–FFA mole ratios ranging from 20:1 to 80:1. It has been found that a 60:1 methanol–FFA mole ratio and 5 wt% catalyst at 60°C and 500 rpm or above provided a final acid value lower than 1 mg KOH/g oil within 60 min. A kinetic model has been proposed with second‐order kinetics for both the forward and backward reactions. The effect of temperature on the reaction rate constants and equilibrium constant has been determined using Arrhenius and von't Hoff equations, respectively. The heat of reaction was found to be ?11.102 kJ/mol.     

Producing biodiesel from high free fatty acids waste cooking oil assisted by radio frequency heating

Efficient biodiesel conversion from waste cooking oil with high free fatty acids (FFAs) was achieved via a two-stage procedure (an acid-catalyzed esterification followed by an alkali-catalyzed transesterification) assisted by radio frequency (RF) heating. In the first stage, with only 8-min RF heating the acid number of the waste cooking oil was reduced from 68.2 to 1.64 mg KOH/g by reacting with 3.0% H₂SO₄ (w/w, based on oil) and 0.8:1 methanol (weight ratio to waste oil). Then, in the second stage, the esterification product (primarily consisting of triglycerides and fatty acid methyl esters) reacted with 0.91% NaOH (w/w, based on triglycerides) and 14.2:1 methanol (molar ratio to triglycerides) under RF heating for 5 min, and an overall conversion rate of 98.8 ± 0.1% was achieved. Response surface methodology was employed to evaluate the effects of RF heating time, H₂SO₄ dose and methanol/oil weight ratio on the acid-catalyzed esterification. A significant positive interaction between RF heating time and H₂SO₄ concentration on the esterification was observed.     

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.     

Rapid and complete extraction of free fatty acids from oilseeds for acid value determination

The rapidity and uncertainty of the acid value determination in oilseeds are defined by the rate and completeness of the free fatty acid extraction. The strategy of reagent development for extraction has been discussed, and a set of reagents that provide rapid and complete extraction has been obtained. The set consists of two reagents. Reagent A contains triethanolamine in a mixture of water, isopropanol, and heptane. Reagent B contains a strong acid and inorganic salt in water. Reagent A allows the carrying out of rapid (1–2 min) solid-liquid extraction of the free fatty acids and some other acids from oilseeds. Reagent B provides the separation of the free fatty acids only into the heptane phase (∼5 min), which can be used directly for the free fatty acid determination. Two techniques for this determination have been applied: pH-metric and titrimetric. The advantages of the proposed set of reagents are described.     

Synthesis of spinel ferrite and its role in the removal of free fatty acids from deteriorated vegetable oil

Deterioration and loss of quality of vegetable oil is a big challenge in the food industry. This study investigated the synthesis of nickel ferrite (NiFe₂O₄) via co-precipitation method and its use for the removal of free fatty acids (FFAs) in deteriorated vegetable oil. NiFe₂O₄ was characterized using Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TG) analysis, Brunauer–Emmett–Teller (BET) surface area, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Synthesis of NiFe₂O₄ was confirmed by characterization, which revealed a BET surface area of 16.30 m²·g^-1 and crystallite size of 29 nm. NiFe₂O₄ exhibited an adsorption capacity of 145.20 L·kg^-1 towards FFAs with an 80.69% removal in a process, which obeys Langmuir isotherm and can be described by the pseudo-second-order kinetic model. The process has enthalpy (ΔH) of 11.251 kJ·mol^-1 and entropy (ΔS) of 0.038 kJ·mol^-1·K^-1 with negative free energy change (ΔG), which suggests the process to be spontaneous and endothermic. The quantum chemical computation analysis via density functional theory further revealed the sorption mechanism of FFAs by NiFe₂O₄ occurred via donor–acceptor interaction, which may be described by the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The study showed NiFe₂O₄ to be a potential means that can remove FFAs from deteriorated vegetable oil.     

Extraction of pollen lipids by SFE‐CO2 and determination of free fatty acids by HPLC

Rape bee pollen lipids obtained by petrol ether extraction (PEE) or supercritical fluid (carbon dioxide) extraction (SFE) were compared with regard to their free fatty acid (FFA) components. Optimal SFE conditions were selected by carrying out the Taguchi method with an OA9 (3³) matrix design, and are as follows: extraction pressure at 35 MPa, temperature at 45 °C, and dynamic extraction time at 90 min. The lipid yield based on PEE was 7.42 wt‐% and the extracts of the desired analytes based on SFE varied in the range of 3.23–5.58 wt‐% under different conditions. With the optimized procedure, the lipid yield was 6.09 wt‐%. The FFA in the lipids were separated with a pre‐column derivation method and 1‐[2‐(p‐toluenesulfonate) ethyl]‐2‐phenylimidazole [4,5‐f]9,10‐phenanthrene as labeling regent, followed by high‐pressure liquid chromatography (HPLC) with fluorescence detection. HPLC analysis shows that the lipids contain abundant unsaturated fatty acids (UFA) in high to low concentrations as follows: linolenic acid (18:3), oleic acid (18:1), linoleic acid (18:2), nervonic acid (24:1), and lignoceric acid (20:4). The UFA contents in the SFE extracts were higher than those after PEE. The results indicated that SFE under suitable conditions is more selective than conventional PEE with regard to lipid extraction and preservation of their quality.     

Determination of trans fatty acids and fatty acid profiles in margarines marketed in spain

Two gas chromatography (GC) procedures were compared for routine analysis of trans fatty acids (TFA) of vegetable margarines, one direct with a 100-m high-polarity column and the other using argentation thin-layer chromatography and GC. There was no difference (P>0.05) in the total trans 18∶1 percentage of margarines with a medium level of TFA (∼18%) made using either of the procedures. Both methods offer good repeatability for determination of total trans 18∶1 percentage. The recoveries of total trans isomers of 18∶1 were not influenced (P>0.1) by the method used. Fatty acid composition of 12 Spanish margarines was determined by the direct GC method. The total contents of trans isomers of oleic, linoleic, and linolenic acids ranged from 0.15 to 20.21, from 0.24 to 0.99, and from 0 to 0.47%, respectively, and the mean values were 8.18, 0.49, and 0.21%. The mean values for the ratios [cis-polyunsaturated/(saturated +TFA)] and [(cis-polyunsaturated + cis-monounsaturated)/(saturated +TFA)] were 1.25±0.39 and 1.92±0.43, respectively. Taking into account the annual per capita consumption of vegetable margarine, the mean fat content of the margarines (63.5%), and the mean total TFA content (8.87%), the daily per capita consumption of TFA from vegetable margarines by Spaniards was estimated at about 0.2 g/person/d.     

反式脂肪酸测定方法的研究

简要介绍了反式脂肪酸(TFA)的生成途径及主要的食物来源,反式脂肪酸对人体健康的主要危害和影响,综述了反式脂肪酸的分析检测方法如气相色谱法、红外光谱法、Ag离子色谱技术、毛细管电泳法等,并比较了各种方法的优缺点。     

Determination of free fatty acids in palm oil by near-infrared reflectance spectroscopy

A near-infrared (NIR) spectroscopy calibration was developed for the determination of free fatty acids (FFA) in crude palm oil and its fractions based on the NIR reflectance approach. A range of FFA concentrations was prepared by hydrolyzing oil with 0.15% (w/w) lipase in an incubator at 60°C (200 rpm). Sample preparation was performed in Dutch cup, and the spectra were measured in duplicate for each sample. The optimized calibration models were constructed with multiple linear regression analysis based on C=O overtone regions from 1850–2050 nm. The best wavelength combinations were 1882, 2010, and 2040 nm. Multiple correlation coefficients squared (R ²) were: 0.994 for crude palm oil, 0.961 for refined-bleached-deodorized (RBD) palm olein, and 0.971 for RBD palm oil. Calibrations were validated with an independent set of 8–10 samples. R ² of validation were 0.997, 0.943, and 0.945, respectively. The developed method was rapid, with a total analysis time of 5 min, and environmentally friendly, and its accuracy was generally good for raw-material quality control.