分提橄榄油中主要脂肪酸成分傅里叶变换红外光谱法测量（英）

为了测量从橄榄油中分提的高、低熔点油脂的脂肪酸成分,在4 000～600 cm-1 的范围测量了31个含有不同脂肪酸成分植物油的傅里叶变换红外光谱,用于建立偏最小二乘（PLS）回归分析校正模型。在油脂的傅里叶变换红外光谱变量和脂肪酸组成变量之间建立了交叉验证的PLS校正模型。为了校正油酸和亚油酸含量,在4?000～600 cm-1 的频率范围,经平滑,二阶导数,规范化处理的红外光谱获得了最好的交叉验证校正模型和最佳的预测结果。PLS校正模型预测结果表明,与高熔点橄榄油（油酸,72.29%,亚油酸,9.98%）相比,低熔点橄榄油含有较高的油酸含量和亚油酸含量（油酸,77.46%,亚油酸,12.51%）,预测的结果与气相色谱测量的结果有很好的一致性。建立的PLS校正模型预测橄榄油的不饱和脂肪酸含量具有较好的相关性。该研究为分提油脂质量的判别评价提供了便捷的方法。     

拉曼光谱结合UVE-SVR算法预测加热食用油反式脂肪酸的含量

为实现拉曼光谱技术对食用油加热后反式脂肪酸(TFAs)含量的快速预测,将3种食用油在190℃下(常用煎炸温度)进行不同时间加热,每个样品采集36条拉曼光谱。首先,采用多项式平滑与标准正态变量变换(SNN)对原始光谱数据进行预处理,以去除背景和噪音的干扰,然后采用无信息变量消除法(UVE)对光谱数据进行特征变量筛选,最后分别基于全谱数据和筛选的特征光谱变量建立定性和定量分析模型,并对试验结果进行对比分析。结果表明,基于筛选后的变量,运用Fisher判别分析(FDA)建立定性判别模型,其判别正确率由40%~50%提升至90%以上,表明筛选后的变量能较好表征样品的特征信息;分别基于筛选变量和全谱数据,运用偏最小二乘回归(PLSR)、BP神经网络(BPNN)和支持向量回归机(SVR)方法,建立不同样品中TFAs含量的数学预测模型。通过对预测结果对比分析,表明UVE结合SVR方法具有良好的检测效果,菜籽油、大豆油、玉米油的测试集R²分别从0.850 4、0.943 5和0.753 4升至0.952 6、0.954 8和0.958 5。因此,利用UVE-SVR方法不仅简化了预测模型,提高了模型的稳定性和精度,也为食用油中TFA的快速检测提供了一种可行的方法。     

Differentiation of refined and virgin edible oils by means of the trans- and cis-phytol isomer distribution

The differentiation of nonrefined (e.g., cold-pressed) and refined edible oils is an important task in food control because of the higher commercial value of the former. Here, we explored the suitability of the relative abundance of cis-phytol as a marker for authentication of nonrefined edible oils. Phytol, the tetramethyl-branched, monoenoic alcohol, is found widespread in nature as a part of chlorophyll. In chlorophyll, only trans-phytol is found. In this study, we present a method for the analysis of the phytol isomers, considering that traces of cis-phytol (contributing 0.1% to the phytol content) can be determined next to trans-phytol. For this purpose, phytol was gathered with the unsaponifiable matter from the oil, trimethylsilylated, and analyzed by gas chromatography coupled to mass spectrometry. With this method, 27 samples of edible oils (16 refined and 11 nonrefined edible oils) were analyzed for the abundance of cis-phytol relative to trans-phytol. In the nonrefined oils (e.g., olive oil, rapeseed oil, maize oil, and sunflower oil), cis-phytol contributed 0.1% (n = 3) or less (n = 8) to the phytol content. In contrast, the refined olive oils (n = 4) contained a share of 1.3-3% cis-phytol; the refined rapeseed oil (n = 3) contained a share of 0.7-1.0% cis-phytol; and the refined sunflower oil (n = 4) contained a share of 0.3-0.9% cis-phytol. Only one refined pomegranate kernel did not contain cis-phytol. The phytol concentration was not suited to distinguish nonrefined from refined oils. In contrast, our data suggest that the virtual absence of cis-phytol can be used as a marker for nonrefined (e.g., cold-pressed) edible oils.     

ATR-Fourier transform mid-infrared spectroscopy for determination of trans fatty acids in ground cereal products without oil extraction

Fourier transform mid-infrared (FT-IR) spectroscopy was investigated as a method of analysis for trans fatty acid content of cereal products without the need for prior oil extraction. Spectra were obtained, with an FT-IR spectrometer equipped with an attenuated total reflectance (ATR) device, of ground samples pressed onto the diamond ATR surface, and trans fatty acids were measured by a modification of AOAC Method 996.01. Partial least-squares (PLS) models were developed for the prediction of trans fatty acids in ground samples using several wavenumber selections on the basis of bands related to lipids. The models (n = 79) predicted trans fatty acids in ground samples with standard error of cross-validation (SECV) of 1.10-1.25 (range 0-12.4) % and R2 of 0.85-0.88 and in validation samples (n = 26) with standard error of performance (SEP) of 0.96-1.12 (range 0-12.2) % and r2 of 0.89-0.92, indicating sufficient accuracy for screening. Sample trans fatty acid % was predicted as accurately with the fingerprint region (1500-900 cm(-1)) as with the entire range (4000-650 cm(-1)) indicating, in concert with the regression coefficients, the importance of the isolated trans double bonds at 966 cm(-1) in development of the model. Data is also presented on prediction of trans fatty acids using the spectra of residual oil films on the ATR surface after removing the solid portion of the sample.     

Rapid determination of free fatty acids in poultry feed lipid extracts by SB-ATR FTIR spectroscopy

A simple, rapid, and reproducible method has been developed for the quantitative determination of free fatty acid (FFA) content in lipids extracted from poultry feeds by Fourier transform infrared (FTIR) spectroscopy with the use of a single-bounce attenuated total reflectance (SB-ATR) accessory. An FTIR calibration curve was prepared by gravimetrically adding oleic acid (15-37%) to pure refined, bleached, and deodorized (RBD) canola oil and measuring the area of the COOH absorption band at 1710 cm-1. The oil from each of 12 poultry feed formulations was extracted using conventional Soxhlet extraction, and after evaporation of the solvent, the FFA content was determined by the conventional AOCS titrimetric procedure and by the SB-ATR/FTIR method. The SB-ATR/FTIR FFA predictions were related to those determined by the AOCS titrimetric method by linear regression, producing an R value of 0.999 and a SD of +/-0.28% FFA. Time-course spectra collected as lipids extracted into hexane indicated that a 15 min extraction was adequate to obtain a representative sample for FFA determination, with further extraction resulting in little, if any, change in the proportion of FFA in the lipid extract. Only a small volume of the hexane extract ( approximately 20 mL) yielded sufficient material for the SB-ATR/FTIR analysis. Thus, by shortening the extraction time and taking a small sample so as to reduce solvent removal time, the SB-ATR/FTIR procedure provides a very simple and rapid means of determining the FFA content of poultry feed lipids.     

Cluster analysis applied to the exploratory analysis of commercial spanish olive oils by means of excitation-emission fluorescence spectroscopy

Olive oil fluorescence is related to oil composition. Here it is shown that the natural clustering of different types of commercial Spanish olive oils depends on their fluorescence excitation-emission matrices (EEMs). Fifty-six commercial samples of olive oil (29 virgin olive oils, 20 pure olive oils, and 7 olive-pomace oils) were used. The clustering method was hierarchical agglomerative clustering using the Euclidean distance as a similarity measure and the average linkage. Two spectral ranges were considered (which either contained the fluorescence peak of the chlorophylls or did not), and various methods for preprocessing the fluorescence spectra were compared. The oils were clearly distinguished using the unfolded EEMs measured between lambda(ex) = 300-400 nm and lambda(em) = 400-600 nm. The optimal preprocessing was normalization of the unfolded spectra followed by column autoscaling. Also shown are the advantages of using second-order data (EEMs) instead of first-order data (a single fluorescence spectrum) for each sample.     

Synchronous fluorescence spectroscopy of edible vegetable oils. Quantification of tocopherols

The study demonstrates the application of front face and right angle synchronous fluorescence spectroscopy for the characterization of edible oils. The method enables monitoring of tocopherols, pheophytins, and other fluorescent components in edible oils. Principal component analysis of synchronous fluorescence spectra revealed sample clustering according to the type of oil. Partial least-squares regression was utilized to develop calibration models between fluorescence spectra and total tocopherol content determined by HPLC. The regression models showed a good ability to predict tocopherol content. The best fitting results were obtained for 1% v/v diluted oils and for bulk samples using the entire spectrum, yielding the regression coefficient, r, of 0.991, and root mean square error of cross-validation of approximately 8%. The results presented confirm the capabilities of the fluorescence techniques as a tool for the analysis of edible oils.     

trans-Free margarines prepared with canola oil/palm stearin/palm kernel oil-based structured lipids

Structured lipids (SLs) for formulating trans-free margarines were synthesized by lipase-catalyzed interesterification of the blends of canola oil (CO), palm stearin (PS), and palm kernel oil (PKO) in weight ratios (CO/PS/PKO) of 40:60:0, 40:50:10, 40:40:20, 40:30:30, 50:30:20, and 60:25:15. The atherogenicity was determined using fatty acid profiles. We also determined the physical properties (melting/crystallization profiles, solid fat content, polymorphism, and microstructure) of SLs and the textural properties of margarines made with the SLs. The SLs from the 50:30:20 and 60:25:15 blends had atherogenic indices similar to or lower than those of the commercial trans (CTMF) and similar to the trans-free margarine fats (CTFMF). SLs from the blends with PKO contained a wide range of fatty acids (C6-C20) and had more beta' than beta polymorphs. Margarines made with SLs from 50:30:20 and 60:25:15 blends possessed similar hardness, adhesiveness, or cohesiveness to margarines made with CTMF and CTFMF, respectively. Therefore, CO/PS/PKO-based SLs were suitable for formulating trans-free margarines with low atherogenicity and desirable textural properties.     

Oxidative stability measurement of high-stability oils by pressure differential scanning calorimeter (PDSC)

High-stability oils are used as coatings on food products that require long shelf life. The high stability oils produced from high-oleic oils require less processing and bring additional nutritional benefits such as lower trans and saturated fat contents. Accurate and reproducible oxidative stability measurement of these oils is necessary to assess the performance. The accelerated oxidative stability measurement method often used in the fats and oils industry, the oxidative stability index (OSI, AOCS Cd 12b-92) is unreliable for higher stability oils due to poor reproducibility. This study presents a pressure differential scanning calorimetry (PDSC) method, which is highly reproducible and versatile and applies to oils from low to very high oxidative stability. PDSC has been used in industrial applications such as lubricants (ASTM D 6186-98) and measures the oxidative induction time (OIT) of oils under high temperature and pressure in the presence of pure oxygen. The OITs of a number of hydrogenated oils with different unsaturation and oxidative stability are measured. Unlike OSI data, the PDSC OIT measurement is highly reproducible and precise and requires only a small sample and a couple of hours. The regression analysis of the PDSC data indicated the natural log OIT of all samples linearly correlated with the temperature. The equation derived from this relationship helps to compare the oxidative stabilities of the same or different oils determined at different temperatures. The development of this method into an approved method will benefit the fats/oils and food industry.     

近红外光谱快速检测食用油必需脂肪酸

为了建立食用油必需脂肪酸快速检测的方法,该研究提出了基于近红外光谱技术检测食用油中α-亚麻酸和亚油酸含量的快速测定方法。对光谱信息分别采用偏最小二乘回归方法(PLS)和最小二乘支持向量机(LS-SVM)建立模型。比较了多种光谱预处理方法对模型预测能力的影响。结果表明对于亚油酸含量的预测,采用Savitzky-Golay平滑法结合多元散射校正(MSC)的光谱预处理所建立的LS-SVM模型最优。预测集的决定系数(R2)、预测均方根误差(RMSEP)和剩余预测偏差(RPD)分别达到了0.989,0.0161和9.4783。对于α-亚麻酸含量的预测,采用Savitzky-Golay平滑法结合标准正态变换(SNV)的光谱预处理所建立的LS-SVM模型最优。α-亚麻酸含量预测结果的R2、RMSEP和RPD为0.972,0.0036和6.0561,据此表明,应用近红外光谱技术能够检测食用油中α-亚麻酸和亚油酸的含量,为快速检测食用油的必需脂肪酸提供了参考。     

IUPAC gas chromatographic method for determination of fatty acid composition: collaborative study.

An international collaborative study of IUPAC methods II.D.19 and II.D.25 for preparation and GLC analysis of fatty acid methyl esters was begun in 1976. The IUPAC methodology, applicable to animal and vegetable oils and fats and fatty acids from all sources, contains special instructions for preparation and analysis of methyl esters of fatty acids containing 4 or more carbon atoms (analysis of milk fat). Twenty-three collaborators participated in the analysis of 5 known mixtures, 4 vegetable oils, 1 fish oil, and 2 butterfats. Several blind duplicate samples were included. The experimental data were subjected to statistical analysis to examine intra- and interlaboratory variation. Reproducibility and accuracy data for the higher fatty acid (14:0-22:1) mixtures and fish and vegetable oils were satisfactory and were in good agreement with results from an AOCS Smalley Committee check sample program involving analysis of the same samples. Typical coefficients of variation (%) at various concentrations were 15 (2% level), 8.5 (5% level), 7 (10% level), and 3 (50% level). Low recoveries and poor reproducibility were characteristics of results obtained for butyric acid in the butterfat and related known mixtures. A coefficient of variation of about 19% was found for analysis of butyric acid in butterfat, vs coefficients of variation in the range of 4-13% for similar levels of other components in butterfat and other samples. The IUPAC methodology for GLC analysis of fats and oils other than milk fats has been adopted by the AOAC as official first action to replace the current GLC method, 28.063-28.067.     

Gas chromatographic assay of supplemental vitamin E acetate concentrates: collaborative study

A gas chromatographic (GC) method for determination of supplemental alpha-tocopheryl acetate in high potency vitamin E powders and oils was collaboratively studied as an alternative to the AOAC colorimetric method (43.147-43.151, Emmerie-Engel), which requires saponification, extraction of the saponifiable fraction, and quantitation by colorimetry. The simpler GC procedure requires only extraction and/or enzymatic digestion and dilution before quantitation. Six blind duplicates were distributed to 10 laboratories; all 10 returned results. Repeatability (sr) and reproducibility (sR), % vitamin E/g, for the feed oil concentrates was 1.1 and 1.3, respectively; for the feed adsorbates 1.0 and 1.5; and for the spray-formulated powders 1.4 and 1.3. These results compare favorably with results obtained in a comparison study of the GC and Emmerie-Engel methods conducted by BASF in 1985. The method has been approved interim official first action for determination of alpha-tocopheryl acetate in vitamin E acetate concentrates as an alternative for those products only to AOAC colorimetric method 43.147-43.151.     

Rapid magnetic solid-phase extraction based on magnetic multiwalled carbon nanotubes for the determination of polycyclic aromatic hydrocarbons in edible oils

In this study, magnetic multiwalled carbon nanotubes were fabricated by a simple method and applied to magnetic solid-phase extraction (MSPE) of eight heavy molecular weight polycyclic aromatic hydrocarbons (PAHs) including chrysene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene and benzo[g,h,i]perylene from edible oil samples. Several parameters affecting the extraction efficiency were investigated, including the type and volume of desorption solvent, extraction and desorption time, washing solution and the amount of sorbent. Under the optimized conditions, a simple and effective method for the determination of PAHs in edible oils was developed by coupling with gas chromatography-mass spectrometry (GC-MS). The whole pretreatment process was rapid, and it can be accomplished within 10 min. The limits of quantitation for the target PAHs were found to be 0.34-2.9 ng/g. The recoveries in oil sample were in the range 87.8-122.3% with the RSDs less than 6.8% (intraday) and 9.6% (interday). This method was successfully applied to the analysis of PAHs in seven kinds of edible oils from local markets.     

Usefulness of the frequency data of the fourier transform infrared spectra to evaluate the degree of oxidation of edible oils

The oxidation process of 13 edible oil samples with different proportions of oleic, linoleic, and linolenic acyl groups has been studied using Fourier transform infrared spectroscopy. The oxidation experiments were carried out by heating the samples in a convection oven at 70 degrees C. Duplicate spectra were recorded from a film of pure oil between two disks of KBr for each sample every day during the course of the oxidation, and frequency data of each band of the spectrum were collected automatically. Changes in the values of the frequency of most of the bands of the spectra were observed. The shiftings of the frequency value of specific bands allowed one to distinguish between the different stages of the oxidation process and to establish the oxidation degree of each oil sample. This methodology could be useful to evaluate the oxidative stability of edible oils in a simple, fast, and accurate way.     

Measurement of conjugated linoleic acid (CLA) in CLA-rich potato chips by ATR-FTIR spectroscopy

A conjugated linoleic acid (CLA)-rich soy oil has been produced by photoisomerization of soy oil linoleic acid. Nutritional studies have shown that CLA possesses health benefits in terms of reducing certain heart disease and diabetes risk factors. Potato chips are snacks that are readily produced in the CLA-rich soy oil containing CLA levels similar to those of the oil used for frying. The objective of this study was to develop an FTIR method to rapidly determine the CLA content of oil in potato chips. Photoirradiated soy oil samples with ～25% total CLA were mixed with control soy oil, and 100 soy oil samples with total CLA levels ranging from 0.89 to 24.4% were made. Potato chips were fried using each of these 300 g CLA rich soy oil mixtures at 175 °C for approximately 3 min. Duplicate GC-FID fatty acid analyses were conducted on oil extracted from each batch of potato chips. The chip samples were ground and then scanned using ATR-FTIR spectroscopy with the aid of a high-pressure clamp, and duplicate spectra of each sample were averaged to obtain an average spectrum. Calibration models were developed using PLS regression analysis. These correlated the CLA isomer concentrations of potato chips obtained by GC-FID fatty acid analysis with their corresponding FTIR spectral features. The calibration models were fully cross validated and tested using samples that were not used in the calibration sample set. Calibrations for total CLA, trans,trans CLA, trans-10,cis-12 CLA, trans-9,cis-11 CLA, cis-10,trans-12 CLA, and cis-9,trans-11 CLA had coefficients of determinations (R2v) between 0.91 and 0.96 and corresponding root-mean-square error of prediction (RMSEP) ranging from 0.005 to 1.44. The ATR-FTIR technique showed potential as a method for the determination of the CLA levels in unknown potato chip samples.     

Comparison of two methods for determination of total solids content of milk: collaborative study

Ten laboratories analyzed 9 pairs of blind duplicate raw milk samples for total solids. A direct forced air oven method (4 h at 100 degrees C) and a modification of the AOAC predry method (16.032) were used. Preliminary evaluation of the modified AOAC method indicated that blank determinations were necessary. Total solids content ranged from 12.0 to 14.6%. Average repeatability standard deviations (Sr) of the direct forced air oven and modified AOAC methods were 0.019 and 0.017, respectively. Average reproducibility standard deviations (SR) of the direct forced air oven and the modified AOAC methods were 0.042 and 0.047, respectively. Average repeatability relative standard deviations (RSDr) for the direct forced air oven and the modified AOAC methods were 0.149 and 0.136%, respectively; average reproducibility relative standard deviations (RSDR) were 0.327 and 0.370%, respectively. Mean repeatability values (r) and reproducibility values (R) were 0.054 and 0.118 for the direct forced air oven method and 0.049 and 0.133 for the modified AOAC method, respectively. The mean test result of the direct forced air oven method (12.7293%) was comparable to that for the modified AOAC method (12.7273%). The modification of AOAC method 16.032 and the direct forced air oven method have been approved interim official first action.     

Contribution of phospholipid pyrrolization to the color reversion produced during deodorization of poorly degummed vegetable oils

The Ehrlich reaction was optimized to determine the formation of pyrrolized phospholipids in edible oils in an attempt to understand the color reversion produced during the deodorization of poorly degummed edible oils. The procedure consisted of the treatment of the oil with p-(dimethylamino)benzaldehyde in tetrahydrofuran/2-propanol at a controlled acidity and temperature and the spectrophotometric determination of adducts produced. The extinction coefficient of Ehrlich adducts was calculated by using 1-[1-(2-hydroxyethyl)-1H-pyrrol-2-yl]propan-1-ol (1) as a standard and was 15 300 M(-)(1) cm(-)(1). The response was linear and reproducible within the range of 0.334-48.6 microM of compound 1. When the assay was applied to a soybean oil treated with 100-1000 ppm of phosphatidylethanolamine and submitted to deodorization, the formation of pyrrolized phospholipids was observed at the same time that the disappearance of the phospholipid and the oil darkening were produced. The main changes were observed during the first steps of the deodorization process, when the oil was heated between 80 and 160 degrees C. During the initial heating of the oil until achieving 200 degrees C, oil darkening, phosphatidylethanolamine disappearance, and pyrrolized phospholipid formation were correlated, therefore suggesting a contribution of phospholipid pyrrolization to the oil darkening produced.     

Interpretation of Fourier transform Raman spectra of the unsaponifiable matter in a selection of edible oils.

The unsaponifiable matter of edible oils is a source of information for their characterization and authentication. FT-Raman spectroscopy has been applied with success to the determination of the spectra of the unsaponifiable matter of varietal olive oils as well as other refined and crude edible oils. The spectra of the major unsaponifiable series of compounds (squalene, sterolic, and terpenic alcoholic fractions), together with beta-carotene and lutein, have been used to explain the most prominent bands found in the spectra of the unsaponifiable matter of 15 edible oil samples. The order of the scattering intensities of the varietal olive oils agrees with the results obtained by chromatography. An unsupervised multivariate statistical analysis of selected bands points out differences between olive oils and the other seed oils and also among varietal virgin olive oils.     

Modified arabinoxylan-based films. Part B. Grafting of omega-3 fatty acids by oxygen plasma and electron beam irradiation

Arabinoxylans (AXs) are byproducts of the cereal milling industry. To obtain high-value products, AXs have been used as a film-forming agent. Hence, AX-based films are poor water vapor barriers. The objectives of this study were to graft omega-3 (omega3) fatty acids onto AX polymeric chains by using two new technologies: cold plasma and electron beam (EB) irradiation. Results show that the surface hydrophobicity of the modified films is higher than that of a waxy coating or a low-density polyethylene (LDPE) film. In addition, FTIR spectroscopy analysis reveals vibration bands attributed to new chemical functions. Finally, a decrease in water vapor permeability (WVP) is obtained for the film treated with the alpha-linolenic acid-rich oil. This result could be explained by a better diffusion of this shorter polyunsaturated fatty acid into the AX network. Linseed oils provide better barrier properties and a higher surface hydrophobicity than oils extract from marine oils. Edible oils were chosen for edible application of these films to retard moisture transfers in stuffed biscuits.     

Crystallization behavior and texture of trans-containing and trans-free palm oil based confectionery fats

The objective of this study was to gain insight into the role of trans fatty acids in determining the crystallization behavior and texture of palm-based confectionery fats. Therefore, the isothermal crystallization behavior of two series, each of three fats, one trans-containing and one trans-free, was examined by pNMR, DSC, and rheology. Furthermore, the hardness of these samples was examined at three different storage times at 10 degrees C. All of the trans free samples showed a two-step crystallization at 10 degrees C which is hypothesized to be an alpha-mediated beta' crystallization for two of the samples and a fractionated crystallization in the beta' polymorph for the third, while the trans-containing fats crystallized in a single step, probably a direct beta' crystallization. The trans-containing fat series clearly crystallized faster than the trans-free fat series and also yielded higher hardness values at all storage times investigated. The presence of trans fatty acids seems to reduce the effect of compositional variations on the crystallization process. For the trans free fats, chemical composition was much more critical in determining the crystallization rate, the SFC, and the final hardness value.