Determination Of Free Fatty Acids Research Articles

A Comprehensive Study for Determination of Free Fatty Acids in Selected Biological Materials: A Review.

The quality of oil is highly dependent on its free fatty acid (FFA) content, especially due to increased restrictions on renewable fuels. As a result, there has been a growing interest in free fatty acid determination methods over the last few decades. While various standard methods are currently available, such as the American Oil Chemists Society (AOCS), International Union of Pure and Applied Chemistry (IUPAC), and Japan Oil Chemists' Society (JOCS), to obtain accurate results, there is a pressing need to investigate a fast, accurate, feasible, and eco-friendly methodology for determining FFA in biological materials. This is owing to inadequate characteristics of the methods, such as solvent consumption and reproducibility, among others. This study aims to investigate FFA determination methods to identify suitable approaches and introduce a fresh perspective.

Development and application of a sensitive liquid chromatography-tandem mass spectrometry method for the quantitative analysis of 11 free fatty acids in human serum using a derivatisation strategy

A stable isotope dilution–liquid chromatography–tandem mass spectrometry method based on a derivatisation strategy involving an N,N'-carbonylimidazole solution (CDI) with 4-(dimethylamino)-benzenemethanamine was developed for the determination of 11 free fatty acids (FFAs) in human blood samples. Serum samples were subjected to liquid‒liquid extraction and centrifuged, and the supernatant was collected for a two-step derivatisation reaction with a CDI and 4-(dimethylamino)-aniline acetonitrile solution. The derivatised solution was separated on a ACQUITY UPLC HSS T3 column (2.1 × 50 mm, 1.8 µm) column with a mobile phase consisting of water–acetonitrile in gradient elution and then detected by tandem mass spectrometry using electrospray ionisation (ESI) and multiple reaction monitoring (MRM) in positive ion mode and quantified using the isotope internal standard method. The effects of the derivatisation reaction time, temperature and concentration of derivatisation reagents on the response values of the analytes were investigated. The optimal conditions were as follows: 1.0 mg mL−1 CDI acetonitrile solution at 25 °C for 25 min, followed by a reaction with a 1.0 mg mL−1 4-(dimethylamino)-benzenemethanamine acetonitrile solution at 70 °C for 30 min. Under the optimal conditions, the limits of detection (LODs) of the 11 FFAs were in the range of 3.0–14.0 ng mL−1; the limits of quantification (LOQs) were in the range of 8.0–45.0 ng mL−1; and the mean recoveries ranged from 83.4 to 112.8%, with intraday and interday precisions ranging from 0.7 to 9.1% and 3.7–9.5%, respectively. The experimental method is simple in terms of the pretreatment operation, accurate and reliable, and can be applied to the sensitive determination of FFAs in human blood samples.

Free fatty acid profiling of Greek yogurt by liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis

Yogurt is a fermented dairy product of high nutritional value, very popular in many parts of the world. Free fatty acids (FFAs), which are formed during fermentation, may cause changes in organoleptic properties of yogurt, and thus, the determination of FFAs is of importance. We present a liquid chromatography–high resolution mass spectrometry (LC-HRMS) method, which allows the simultaneous determination of a large set of common and uncommon FFAs in yogurt samples, avoiding any derivatization step. Twenty-five common saturated and unsaturated FAs, together with 21 saturated hydroxy fatty acids (SHFAs) and 17 saturated oxo fatty acids (SOFAs), were analyzed in 26 cow and 7 sheep Greek yogurt samples. A detailed analysis of bioactive SHFAs and SOFAs was carried out in yogurt samples for the first time. Differences at the concentrations of six common FAs and five oxidized FAs between the cow and sheep samples were observed. Based on these FAs, Principal Component Analysis (PCA) allows the discrimination of cow from sheep yogurt samples.

Lipidomics Analysis of Free Fatty Acids in Human Plasma of Healthy and Diabetic Subjects by Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS).

Targeted analytical methods for the determination of free fatty acids (FFAs) in human plasma are of high interest because they may help in identifying biomarkers for diseases and in monitoring the progress of a disease. The determination of FFAs is of particular importance in the case of metabolic disorders because FFAs have been associated with diabetes. We present a liquid chromatography-high resolution mass spectrometry (LC-HRMS) method, which allows the simultaneous determination of 74 FFAs in human plasma. The method is fast (10-min run) and straightforward, avoiding any derivatization step and tedious sample preparation. A total of 35 standard saturated and unsaturated FFAs, as well as 39 oxygenated (either hydroxy or oxo) saturated FFAs, were simultaneously detected and quantified in plasma samples from 29 subjects with type 2 diabetes mellitus (T2D), 14 with type 1 diabetes mellitus (T1D), and 28 healthy subjects. Alterations in the levels of medium-chain FFAs (C6:0 to C10:0) were observed between the control group and T2D and T1D patients.

A feasibility quantitative analysis of free fatty acids in polished rice by fourier transform near-infrared spectroscopy and chemometrics.

Free fatty acids (FFAs) are an important indicator of the freshness and quality of rice. In this study, the vibration response of C-H chemical bonds (-CH3 , -CH2 , H-C=C-H) of FFAs in the near-infrared region was determined by analyzing the standard reagent. In addition, the spectral data of different physical forms of rice and chemometrics, such as partial least squares (PLS), synergy interval-PLS, and competitive adaptive reweighted sampling (CARS), were applied to develop an optimal regression model for rice FFAs determination. The performance of the FFAs model established by using the polished rice granule spectrum (PRG) combined with CARS was the best, the correlation coefficients of the calibration set and prediction set were 0.99 (root mean squared errors of the calibration=2.00mg/100g)and 0.98 (root mean squared errors of the prediction=3.21mg/100g),respectively, and the ratio of performance-to-deviation was 4.50. Compared with the rice powder spectral, the PRG spectral can better retain the information of FFAs. The result shows that NIRS can rapidly, non-destructively, and accurately detect FFAs in rice granules, which will help rice business and food regulatory authorities to establish an early warning mechanism of rice aging. PRACTICAL APPLICATION: Free fatty acids (FFAs) in rice are an important indicator for evaluating the freshness of rice, and their high responsiveness to the deterioration of rice quality. The real-time detection of FFAs in rice can timely adjust the parameters of the rice storage environment, which is very meaningful to ensure the quality of rice.

Voltammetric determination of palmitic acid by electrode modified with reduced graphene oxide.

Palm oil is one of the most produced and traded vegetable oils in the world recently. The quality of palm oil is very important to be examined and one of the quality indices is free fatty acid (FFA) content. Thus, in this study, an electrochemical technique for the determination of FFA as alternative to conventional method (titration method) has been explored. The electrochemical method was developed based on electrochemically reduced graphene oxide (rGO) deposited onto screen printed carbon electrode (SPCE) via drop-casting technique. The modified electrode was characterized by physico-chemical and electrochemical methods, respectively. The voltammetric behaviour of 2-methyl-1,4-naphthaquinone (VK3) in the presence of palmitic acid at the modified electrode was investigated in an acetonitrile/water (3:1) mixture containing 2.5M lithium perchlorate (LiClO4). The electrochemical detection of palmitic acid was based on the voltammetric reduction of VK3 to form corresponding hydroquinone which is proportional to the concentration of palmitic acid. Under optimum condition, the developed method showed a good linear relationship in the concentration ranging from 0.192mM to 0.833mM with the detection limit of 0.079mM. The developed sensor illustrates high sensitivity and rapid detection towards determination of FFA content in palm oil.

Reduced Graphene Oxide/Gold Nanoparticles Modified Screen‐Printed Electrode for the Determination of Palmitic Acid

Palm oil is one of the major oils and fats produced in the world today. The quality of palm oil is crucial to be investigated, and one of the quality indices is free fatty acid (FFA) content. Therefore, in this study, an electrochemical approach for the determination of FFA has been explored as an alternative to replace the conventional method (titration method). The electrochemical method was developed based on electrochemically reduced graphene oxide (rGO) coupled with gold nanoparticles (AuNPs) deposited onto a screen‐printed carbon electrode (SPCE) via drop‐casting technique. The voltammetric behaviour of 2‐methyl‐1,4‐naphthoquinone (VK3) in the presence of palmitic acid at the modified electrode was investigated in an acetonitrile/water mixture containing lithium perchlorate (LiClO4). The electrochemical detection of palmitic acid was based on the voltammetric reduction of VK3 to form the corresponding hydroquinone which is proportional to the concentration of palmitic acid. Under optimum conditions, the developed method showed a good linear relationship towards palmitic acid in the concentration ranging from 0.192 mM to 0.833 mM with the detection limit of 0.015 mM. The exploration of the developed system is expected to achieve high sensitivity and excellent selectivity towards the determination of FFA content in palm oil.

Aktivitas Antioksidan Likopen Buah Tomat (Solanum lycopersicum L.) Terblending dalam Minyak Padat Ikan Lele (Clarias sp)

Research on the antioxidant lycopene of tomato fruit (Solanum lycopersicum L.) blended in frying fat from catfish (Clarias sp) oil has been done. The purpose of this research is to determine the antioxidant activity of tomato lycopene before and after being grounded into frying fat and determine the quality of frying fat after being grounded with tomato lycopene. The antioxidant activity of tomato lycopene is determined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. Analysis of frying fat quality includes determination of pH, determination of FFA (free fatty acid) levels, determination of total fat content, measurement of water content, peroxide number and organoleptic observation. Antioxidant activity of tomato lycopen was very high, namely with inhibition value of 89.79%; 90.34%; 91.49% and 92.10%. Frying fat analysis showed high antioxidant activity of lycopene tomatoes with 50.67% inhibition; 51.63%; 51.39% and 51.23%. The results of the analysis of the quality of frying fat are nearly same with SNI quality standards, except for peroxide numbers.
 Keywords: tomato, lycopene, antioxidants, frying fat, catfish, DPPH

Development of a Liquid Chromatography–High Resolution Mass Spectrometry Method for the Determination of Free Fatty Acids in Milk

The determination of free fatty acids (FFAs) in milk is of importance for quality control, legislative purposes, authentication and product development. We present herein a liquid chromatography–high resolution mass spectrometry method for the direct determination of FFAs in milk. The method involves mild sample preparation, avoids time-consuming derivatization and allows the direct quantification of twenty-two FFAs in a 10-min single run. It was validated and applied in thirteen cow milk and seven goat milk samples. Saturated fatty acids C16:0, C18:0 and unsaturated C18:1 (n-9) were found to be the major components of milk FFAs at concentrations of 33.1 ± 8.2 μg/mL, 16.5 ± 5.3 μg/mL and 14.8 ± 3.8 μg/mL, respectively, in cow milk and at concentrations of 22.8 ± 1.8 μg/mL, 12.7 ± 2.8 μg/mL and 13.3 ± 0.3 μg/mL, respectively, in goat milk. Other saturated and unsaturated FFAs were found in significantly lower quantities. Saturated fatty acids C6:0, C8:0 and C10:0 were found in higher quantities in goat milk than in cow milk. The levels of the important (for human health) odd-chain FFAs C15:0 and C17:0 were estimated in cow and goat milk.

Free Fatty‐Acid Generation and Lipid Oxidation during Dry‐Grind Corn Ethanol Fermentation

AbstractThe formation of free fatty acid (FFA) is an undesirable change during dry‐grind corn ethanol fermentation because it negatively affects biodiesel transformation. The primary objective of this work was to determine where in the process FFA is generated using laboratory‐scale simulation experiments. TLC and GC were used to quantify FFA in the extracted total lipids. Values obtained from FFA determination by titration were also compared with those obtained from TLC‐GC. Results indicate that FFA generation is due to an incremental increase at each step in the process, particularly at the early slurrying and liquefaction stage, and also likely during the continuous backset. Furthermore, laboratory‐based fermentations indicate that the oxidation of linoleic acid in the FFA fraction and possibly in the oil increased the FFA level determined using the titration method. Industrial oil samples collected were shown to be highly oxidized and this led to an overestimation of FFA by 15–24% using the titration method compared to TLC‐GC due to the formation of a secondary oxidation product, acids. Such a discrepancy in FFA quantification and the level of lipid oxidation have not been seen in the literature.

Characterization of E 471 food emulsifiers by high-performance thin-layer chromatography–fluorescence detection

Mono- and diacylglycerol (MAG and DAG) emulsifiers, also known as food additive E 471, are widely used to adjust techno-functional properties in various foods. Besides MAGs and DAGs, E 471 emulsifiers additionally comprise different amounts of triacylglycerols (TAGs) and free fatty acids (FFAs). MAGs, DAGs, TAGs and FFAs are generally determined by high-performance liquid chromatography (HPLC) or gas chromatography (GC) coupled to mass selective detection, analyzing the individual representatives of the lipid classes. In this work we present a rapid and sensitive method for the determination of MAGs, DAGs, TAGs and FFAs in E 471 emulsifiers by high-performance thin-layer chromatography with fluorescence detection (HPTLC–FLD), including a response factor system for quantitation. Samples were simply dissolved and diluted with t-butyl methyl ether before a two-fold development was performed on primuline pre-impregnated LiChrospher silica gel plates with diethyl ether and n-pentane/n-hexane/diethyl ether (52:20:28, v/v/v) as the mobile phases to 18 and 75 mm, respectively. For quantitation, the plate was scanned in the fluorescence mode at UV 366/>400 nm, when the cumulative signal for each lipid class was used. Calibration was done with 1,2-distearin and amounts of lipid classes were calculated with response factors and expressed as monostearin, distearin, tristearin and stearic acid. Limits of detection and quantitation were 1 and 4 ng/zone, respectively, for 1,2-distearin. Thus, the HPTLC–FLD approach represents a simple, rapid and convenient screening alternative to HPLC and GC analysis of the individual compounds. Visual detection additionally enables an easy characterization and the direct comparison of emulsifiers through the lipid class pattern, when utilized as a fingerprint.

Determination of free fatty acids in beer

Free fatty acids (FFA) content of beer affects the ability to form a stable head of foam and plays an important role in beer staling. Moreover, the presence of saturated FAs is related sometimes to gushing problems in beer. The aim of this research was to validate an analytical method for the determination of FFAs in beer. The extraction of FFAs in beer was achieved via Liquid–Liquid Cartridge Extraction (LLCE), the FFAs extract was purified by Solid Phase Extraction (SPE), methylated by boron trifluoride in methanol, and injected into GC-FID system. The performance criteria demonstrate that this method is suitable for the analysis of medium and long chain FFAs in beer. The proposed method was tested on four experimental beers.

Comparison and validation of 2 analytical methods for the determination of free fatty acids in dairy products by gas chromatography with flame ionization detection

Accurate quantification of free fatty acids (FFA) in dairy products is important for quality control, nutritional, antimicrobial, authenticity, legislative, and flavor purposes. In this study, the performance of 2 widely used gas chromatographic flame ionization detection methods for determination of FFA in dairy products differing in lipid content and degree of lipolysis were evaluated. We used a direct on-column approach where the isolated FFA extract was injected directly and a derivatization approach where the FFA were esterified in the injector to methyl esters using tetramethylammonium hydroxide as a catalyst. A comprehensive validation was undertaken to establish method linearity, limits of detection, limits of quantification, accuracy, and precision. Linear calibrations of 3 to 700mg/L (R2>0.999) and 20 to 700mg/L (R2>0.997), and limits of detection and limits of quantification of 0.7 and 3mg/L and 5 and 20mg/L were obtained for the direct injection on-column and the derivatization method, respectively. Intraday precision of 1.5 to 7.2% was obtained for both methods. The direct injection on-column method had the lower levels of limits of detection and quantification, because FFA are directly injected onto the GC as opposed to the split injection used in the derivatization method. However, the direct injection on-column method experienced accumulative column phase deterioration and irreversible FFA absorption because of the acidic nature of the injection extract, which adversely affected method robustness and the quantification of some longer chain FFA. The derivatization method experienced issues with quantification of butyric acid at low concentrations because of coelution with the injection solvent peak, loss of polyunsaturated FFA due to degradation by tetramethylammonium hydroxide, and the periodic emergence of by-product peaks of the tetramethylammonium hydroxide reaction that interfered with the quantification of some short-chain FFA. The derivatization method is more robust, and because the derivatization step can be automated, it is more suitable for routine analysis of FFA in dairy products. However, considerable scope exists to develop an alternative gas chromatography with flame ionization detection method to quantify FFA in dairy products without any limitations that is robust and accurate.

Quantitative analysis of acidity level in virgin coconut oils by Fourier transform infrared spectroscopy and chemometrics

The quality of virgin coconut oil (VCO), together with its health functionalities, is directly related to its freshness and to the levels of free fatty acids (FFA). Thus, the goal of this work was to develop a quantitative model based on partial least squares regression (PLSR) to predict FFA levels (%) in VCO. A total of 72 Brazilian commercial samples classified in accordance to their shelf life was analyzed. FFA levels ranged from 0.3 to 2.3%. FTIR (Fourier transform infrared spectroscopy) spectra were recorded within a range of 3100 to 680 cm−1 and submitted to mathematical preprocessing. Quantitative models were developed by partial least squares regression (PLSR). Excellent predictive results were obtained, indicating that the FFA levels in VCO could be accurately quantified by FTIR. The correlation coefficient (R) and the root mean squared error of prediction (RMSEP) were, respectively, as high as 0.994 and as low as 0.07.Practical applications: According to international standards, acid‐base titration is the reference method for the determination of FFA in oils. This method is laborious and time‐consuming, uses toxic and flammable solvents and it is susceptible to error when detecting the color change of the indicator. Some of the advantages of FTIR over the official acid‐base titration method are the short time and simplicity of analysis. Besides that, it is non‐destructive and it does not require hazardous solvents and reagents. The results shown in this study indicate that FTIR spectroscopy and chemometrics can be successfully applied to the quantitative evaluation of FFA in VCO.The quality of virgin coconut oil (VCO), together with its health functionalities, is directly related to its freshness and to the levels of free fatty acids (FFA). Acid‐base titration is the reference method for the determination of FFA in oils. This method is laborious and time‐consuming, uses toxic and flammable solvents and it is susceptible to error when detecting the color change of the indicator. FTIR is a rapid, non‐destructive, and accurate technique that could overcome some of the drawbacks of titration methodologies and could be easily implemented in routine quality control laboratories. The results shown in this study indicate that FTIR spectroscopy and chemometrics can be successfully applied to the quantitative evaluation of FFA in VCO.

Chromatographic–mass spectrometric determination of free fatty acids in blood plasma and urine using extractive alkylation

A method is proposed for the extractive alkylation of free fatty acids (FFA) in blood plasma and urine for their subsequent chromatographic–mass spectrometric determination as methyl esters. The list of target compounds includes 19 saturated acids (C6–C24) and 20 unsaturated acids (C16–C24), including ω-3, ω-6, ω-9, and polyunsaturated fatty acids. For the simultaneous extraction of FFA from a matrix and derivatization, extractive alkylation with iodomethane was used. The peculiarity and advantage of the method is integration of the stages of extraction and preparation of volatile derivatives under mild conditions. The recovery and conversion are from 60 to 90%. The analytical range was from 0.02 to 20 µg/mL of a sample. The effect of samples storage conditions on the results of measurements is evaluated. The method was tested in the determination of FFA in blood plasma and urine of volunteers and laboratory animals.

Study of UltraHigh Performance Supercritical Fluid Chromatography to measure free fatty acids with out fatty acid ester preparation.

Most lipids are best characterized by their fatty acids which may differ in (a) chain length, (b) degree of unsaturation, (c) configuration and position of the double bonds, and (d) the presence of other functionalities. Thus, a fast, simple, and quantitative analytical technique to determine naturally occurring free fatty acids (FFA) in different samples is very important. Just as for saponified acylglycerols, the determination of FFA's has generally been carried out by high resolution gas chromatography (HRGC). The use of an open tubular capillary column coupled with a flame ionization or mass spectrometric detector provides for both high resolution and quantification of FFA's but only after conversion of all free fatty acids to fatty acid methyl esters (FAME) or pentafluorobenzyl esters. Unfortunately, volatilization of labile ester derivatives of mono- and poly-unsaturated FFA's can cause both thermal degradation and isomerization of the fatty acid during HRGC. The employment of a second generation instrument (here referred to as UltraHigh Performance Supercritical Fluid Chromatograph, UHPSFC) with high precision for modified flow and repeated back pressure adjustment in conjunction with sub-2μm various bonded silica particles (coupled with evaporative light scattering, ELSD, and mass spectrometric, MS, detection) for separation and detection of the following mixtures is described: (a) 31 free fatty acids, (b) isomeric FFA's, and (c) lipophilic materials in two real world fish oil samples. Limits of detection for FFA's via UHPSFC/MS and UHPSFC/ELSD versus detection of FAME's via HRGC/MS are quantitatively compared.

English

The aim of this study was to evaluate in detail the relationship between the basic milk components (fat and protein percentage) and the free fatty acids (FFA) content, as indicators of spontaneous and/or induced lipolysis. The additional aim of the study was to compare the FFA content of milk with respect to spontaneous and induced lipolysis. Milking was carried out in herringbone parlour twice a day. In total, 540 milk samples were obtained for evaluation of spontaneous (n=240) and induced lipolysis (n=300). The milk samples for determination of basic milk components and FFA (lipolysis) levels were collected during four subsequent lactation weeks. Milk samples for spontaneous lipolysis detection were taken directly in parlour immediately after milking using the ICAR methodology and subsequently grouped. Induced lipolysis was observed from bulk milk in time 0, 1, 2, 3, and 4 hours after milking (T0-T4). The evaluation of basic components and FFA content was carried on MILKOSCAN F120 (Foss Electronic; Denmark). Statistical evaluation was carried out using SAS 9.3. (SAS/STAT ® 9.3, 2011). An increase of one percentage of milk fat was equal to 0.318 mmol x 100 g -1 FFA decline (spontaneous lipolysis) or from 0.232 to 0.370 mmol x 100 g -1 FFA decline (induced lipolysis T0-T4) respectively. One percentage increase of milk protein was equal to 1.219 mmol x 100 g -1 FFA increase (spontaneous lipolysis) or 0.421 to 1.531 mmol x 100 g -1 FFA decrease (induced lipolysis T0 - T4) respectively. Significant differences (P<0.01) were detected among FFA content in relation to spontaneous and induced lipolysis evaluated during storage and cooling after milking. The minimal differences were detected between the FFA content during 4 hours cooling and storage of milk in the tank.

Direct detection of free fatty acids in edible oils using supercritical fluid chromatography coupled with mass spectrometry

Determination of free fatty acids (FFAs) in food products is of enormous interest mainly because they are related to the quality and authenticity of the oils. In this study, supercritical fluid chromatography (SFC), followed by an electrospray ionisation triple–quadrupole mass spectrometry (ESI-MS), is shown to provide a novel method for the separation and detection of FFAs in edible oils without any pretreatment. Eight FFAs were separated on a HSS C18 SB column with gradient elution within 3min. Effects of different columns, modifiers and column temperature changes were evaluated. The results indicated the feasibility of this method for the high-throughput determination of individual FFAs with satisfactory correlation coefficients (R2>0.994) and good reproducibility of RSD<13.5% (intraday) and <15.0% (interday). By combined with principal component analysis (PCA), different types of edible oil were successfully distinguished into several categories, showing a potential application for the determination of oil quality or authenticity.

Direct FTIR Analysis of Free Fatty Acids in Edible Oils Using Disposable Polyethylene Films

To simplify a previously reported Fourier transform infrared (FTIR) method for the direct determination of free fatty acid (FFA), a new technique was designed to facilitate mid-FTIR transmission analysis of viscous edible oil samples using disposable polyethylene (PE) films as a spectral acquisition accessory. In the PE-film-based procedures, the viscosities of oil samples were reduced by mixing hexane for allowing the samples to readily deposit onto PE films to form oil films when the solvent evaporated (PE film as spectral background), and the path length of each oil film was normalized to a fixed path length of 0.15 mm. The relationship between FFA content (expressed as percentage of oleic acid) and the absorbance of FFA at 1711 cm−1 relative to a baseline at 1600 cm−1 (baseline was 1600 cm−1) in thenormalized spectra was expressed by a linear calibration equation. To remit the interference from the absorbance due to triglyceride esters (approximately 1,746 cm−1) in the wave numbers used in FFA determination (1,711 cm−1), the intensity of the first overtone of the ester vibration (3,471 cm−1/3,527 cm−1) in FFA-free oil samples was used to determine the intensity of the interfering signal at 1,711 cm−1. Moreover, a linear relationship between the two absorbances was established. Consequently, the absorbance measured at 1,711 cm−1/1,600 cm−1 by FFA determination in the oil samples was corrected for the linear equation. FFA determination in oil samples with known FFA content (0 to 3 %) was carried out in parallel by using the American Oil Chemists’ Society titrimetric method and the PE-film-based FTIR procedures. A comparison indicated that the PE-film-based FTIR method can be used to determine FFA content in different kinds of edible oils.

Rapid assessment of the quality of deep frying oils used by street vendors with Fourier transform infrared spectroscopy

Deterioration of deep frying oils used by street vendors is one of the major food safety concerns. Fourier transform infrared (FTIR) spectroscopy coupled with partial least squares (PLS) regression was applied for rapid evaluation of the quality of deep frying oils collected from different street vendors (n = 109) using various frying processes in Shanghai. The levels of free fatty acids (FFA), total polar compounds (TPC), and viscosity of oils were determined with conventional methods and used as reference values for developing PLS models. The FFA (0.07–1.78 mg (KOH)/g) of all tested frying oils were below the maximum allowed value, while 5.5 % of oils had TPC (3.19–54.47 %) above the maximum allowed value (27 %) based upon the related chinese standards. FTIR coupled with PLS regression resulted in less satisfying results for FFA determination (predictability for soybean oils: R2 = 0.709, SEP = 0.14, RPD = 1.83), but showed great promise for rapid determination of viscosity (model predictability: R2 = 0.921–0.945, SEP = 0.68–0.71, RPD = 3.54–3.98) and TPC (predictability for soybean oils: R2 = 0.790–0.931, SEP = 1.89–2.94, RPD = 2.16–3.55) of frying oils from different commercial settings. Developing separated PLS models for shortening and non-shortening oils improved predictability, particularly for the analysis of TPC.