Shelf‐life prediction of edible fats and oils using Rancimat

Determining the shelf‐life of edible fats and oils under normal storage conditions is a tedious and time‐consuming task. Accelerated tests are therefore frequently used to determine the stability of the products at ambient conditions. However, the mechanisms of lipid oxidation at accelerated conditions may be different from those under normal storage conditions, leading to errors in the shelf‐life predictions. This article describes an automated accelerated method, namely Rancimat, for shelf‐life prediction of edible fats and oils under normal storage conditions, and the effect of its operational parameters on these predictions.     

Bestimmung der Oxidationsstabilität von Fetten und Ölen – Vergleich zwischen der Active Oxygen method (AOCS Cd 12–57) und der Rancimat-Methode

Determination of the Oxidative Stability of Fats and Oils-Comparison between Active Oxygen Method (AOM) and Rancimat Method Oxidative stability is an important parameter for the characterization of fats and oils. The Active Oxygen Method (AOM) can be used to determine this parameter. However, the periodic determinations of peroxide number required with the AOM render this method expensive and labour-intensive. The alternative Rancimat Method is based on the conductometric determination of the volatile decomposition products. As the periodic titrations for the determination of the peroxide number are not necessary, Moreover, in contrast to the AOM, the Rancimat Method does not require expensive chemicals. The induction times t_I determined with the two methods using six different fats and oils show a good correlation. This means that the Rancimat Method gives results equivalent to those of the AOM Method and offers an attractive alternative.     

Relationship between rancimat and active oxygen method values at varying temperatures for several oils and fats

Determination of oxidative stability of different edible oils, fats, and typical fat products was made using the Rancimat method and the active oxygen method. Induction periods (IP) were recorded under controlled conditions at 110, 120, and 130 ± 0.1°C for all products and over a range of 100–160°C for selected fats. A general oil stability evaluation industrial shortenings and vanaspati to be the most stable fats, with IP ranging from 10.00 to 15.47 h. Margarine and butter samples (IP, 4.98–6.04 h) were also found to show fair oxidative stability. Among the extracted and open-market salad-grade cooking oils, rapeseed oil (IP, 4.10 h) and soybean oil (IP, 4.00 h) showed the highest oxidative stability, whereas Salicornia bigelovii oil (IP, 1.40 h) was the least stable. The induction periods of typical fat products ranged from 2.59 to 9.20 h. CV for four determinations were <5.2% for shortening and vanaspati products and <4.3% for various vegetable oils, margarine, butter, and typical fat products. Rancimat IP values obtained at 110, 120, and 130°C were 40–46, 20–25, and 9–13% of active oxygen method values, respectively, corresponding to a decrease in Rancimat IP by a factor of 1.99 with each 10°C increase in temperature. Similarly, in the temperature range 100–160°C, an increase of 10°C decreased the Rancimat IP by a factor of 1.99     

Measurement of the Oxidation Stability of Biodiesel Using a Modified Karl Fischer Apparatus

Oxidative stability is an important parameter in the characterisation of fats and oils. The determination of this parameter with a Rancimat apparatus is very costly. The alternative modified Karl Fischer (KF) apparatus works on the same principle as the Rancimat, i.e., a conductivity based determination of volatile degradation products and automatic plotting of the conductivity against time. The apparatuses were compared by taking five different samples of methyl esters at different temperature ranges. The results indicate that the modified KF apparatus can be used for the determination of oxidation stability of biodiesel with comparable values of sensitivity, repeatability and reproducibility.     

Assessment of thin-film oxidation with ultraviolet irradiation for predicting the oxidative stability of edible oils

The oxidative stability of edible oils and samples of rapeseed oil with added antioxidants, metal ions, phospholipids and oxidized oil was assessed by a method involving oxidation of a thin film of oil with ultraviolet (UV) irradiation at 100°C. Induction times determined by this method were compared with those determined with the Rancimat at 100°C. The two methods agreed well in describing the effects of additives on the stability of the edible oil. Induction times were considerably shorter for the thin-film UV method, and the method may have potential as an accelerated test method for assessing the effect of additives on the oxidative stability of relatively stable oils and fats. The correlation between the Rancimat and the thin-film UV induction times also was assessed at 80°C for rapeseed oil containing additives, but there was no advantage in using the lower temperature alone because the induction times were 2–7 times longer than at 100°C. However, use of two elevated temperatures is likely to improve predictions of stability at lower temperatures, especially for samples containing copper, which have an exceptionally high-temperature coefficient. The thin-film UV method showed a poorer agreement with the Rancimat for comparing the oxidative stability of some fats and oils. For instance, corn oil was more stable than soybean oil in the Rancimat test but the order of stability was reversed in the thin-film UV test. Cocoa butter was much more stable in the Rancimat test than when assessed by the thin-film UV test.     

Analysis of nonvolatile lipid oxidation products in vegetable oils by normal-phase high-performance liquid chromatography with mass spectrometric detection

Nonvolatile triacylglyceride (TAG) oxidation products play an important role in the oxidative degradation of lipids. They serve as a reservoir of oxygen-containing species and hence can act as off-flavor precursors or as initiators for further oxidation reactions. Possible nonvolatile lipid oxidation products are TAG with a hydroperoxy, hydroxy, epoxy, or oxo (ketone or aldehyde) group or combination of these groups. The breakdown of TAG hydroperoxides yields nonvolatile glyceride species with two intact fatty acid chains and one short chain mostly ending in an aldehyde or hydroxy group (2 1/2 glycerides). By means of normal-phase high-performance liquid chromatography (HPLC) with mass spectrometric (MS) detection, non-volatile lipid oxidation products can be separated according to polarity. This results in separation into classes of TAG oxidation products, such as epoxy-TAG, oxo-TAG, hydroperoxy-TAG, hydroxy-TAG and 2 1/2 glycerides, which can be identified using selected ion chromatograms. The retention times of TAG oxidation products on the normal-phase HPLC system and the signal intensity of the MS detector are stable enough to enable quantitative analysis based on external calibration. The normal-phase HPLC-MS method is very suitable for the characterization and quantitation of nonvolatile TAG oxidation products in oxidized TAG reference compounds as well as in real oils or oil phases isolated from emulsions, spreads, or other fat-based food products. This method can give detailed information for the study of lipid oxidation mechanisms. Presented at the 15th Montreux Symposium on Liquid Chromatography/Mass Spectrometry, Montreux, Switzerland, November 9–10, 1998.     

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

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

Application of palm olein in the production of zero‐trans Iranian vanaspati through enzymatic interesterification

The utilization of palm olein in the production of zero‐trans Iranian vanaspati through enzymatic interesterification was studied. Vanaspati fat was made from ternary blends of palm olein (POL), low‐erucic acid rapeseed oil (RSO) and sunflower oil (SFO) through direct interesterification of the blends or by blending interesterified POL with RSO and SFO. The slip melting point (SMP), the solid fat content (SFC) at 10–40 °C, the carbon number (CN) triacylglycerol (TAG) composition, the induction period (IP) of oxidation at 120 °C (IP₁₂₀) and the IP of crystallization at 20 °C of the final products and non‐interesterified blends were evaluated. Results indicated that all the final products had higher SMP, SFC, IP of crystallization and CN 48 TAG (trisaturated TAG), and lower IP₁₂₀, than their non‐interesterified blends. However, SMP, SFC, IP₁₂₀, IP of crystallization and CN 48 TAG were higher for fats prepared by blending interesterified POL with RSO and SFO. A comparison between the SFC at 20–30 °C of the final products and those of a commercial low‐trans Iranian vanaspati showed that the least saturated fatty acid content necessary to achieve a zero‐trans fat suitable for use as Iranian vanaspati was 37.2% for directly interesterified blends and 28.8% for fats prepared by blending interesterified POL with liquid oils.     

Formation of headspace volatiles by thermal decomposition of oxidized fish oilsvs. oxidized vegetable oils

To understand the reasons for differences in oxidative stability among edible oils, the temperature dependence was investigated for the development of volatile lipid oxidation products in fish oils and in vegetable oils. A rapid headspace capillary gas chromatographic method was developed to determine volatile oxidation products of omega-6 (n-6) polyunsaturated fats (pentane and hexanal) and omega-3 (n-3) polyunsaturated fats (propanal) at different decomposition temperatures. Headspace gas chromatographic analyses of partially oxidized menhaden, bonita and sardine oils could be performed at 40°C, whereas soybean, canola, safflower, high-oleic sunflower and high-oleic safflower oils required temperatures greater than 100°C. Volatile formation by thermal decomposition of oxidized oils had lower apparent activation energies in fish oils than in vegetable oils, and significantly higher apparent activation energies in high-oleic oils than in polyunsaturated oils. The activation energy data on headspace volatiles provided another dimension toward a better understanding of the thermal stability of flavor precursors in unsaturated fish and vegetable oils. Presented at the ISF/AOCS joint meeting, Toronto, Canada, May 10–14, 1992.     

Reversed‐phase analysis of triacylglycerols by ultra performance liquid chromatography‐evaporative light scattering detection (UPLC‐ELSD)

An improved reversed‐phase (RP) method has been developed for the analysis of triacylglycerols (TAG) in fats and oils. This method has shown superior performance over traditional reversed‐phase liquid chromatographic (LC) methods in speed and resolution, and equivalent to superior performance in quantitation accuracy (101%–109%) and reproducibility (1.3%–5.8% RSD). The method can easily be adjusted for use with different oils by simple modification of the gradient and run time. Additionally, a mobile phase is used that is compatible with liquid chromatography/mass spectrometry (LC/MS) that when required, can aid in identification of TAG, for which many standards do not exist. This method is suited to a broad number of applications including (but not limited to) research and development of new oils, quality control, production of industrial or edible oils, and seed strain selection.     

Enzymatic Interesterification of Palm Oil and Fractions: Monitoring the Degree of Interesterification using Different Methods

Interesterification is an important modification technique for fats and oils resulting in the redistribution of the fatty acids among the glycerol backbone and thus changing the physico-chemical properties of the modified fat. In this study palm oil, palm olein and soft palm mid fraction (PMF) were subjected to both enzymatic (batchwise) and chemical interesterification. The reaction products were characterized before, during and after interesterification by HPLC, pulsed NMR (p-NMR) and differential scanning calorimetry (DSC). Interesterification led to more uniform triacylglycerol (TAG) compositions with smaller differences in final physico-chemical properties between the studied substrates. The degree of interesterification was evaluated on the basis of TAG composition and solid fat content (SFC). Significant differences between both methods were observed. The degree of interesterification based on SFC is therefore a better tool to evaluate the rate constant of the reaction as the TAG composition method does not take into consideration the formation of positional isomers at the end of the enzymatic process.     

Rapid and direct quantitative analysis of positional fatty acids in triacylglycerols using 13C NMR

There is increasing evidence that the positional fatty acid composition (FAC) of TAG is more important than total FAC with regard to nutrition values of edible oils and fats. A rapid and direct regiospecific analysis of positional fatty acids in TAG using ¹³C NMR was developed to overcome the tedious conventional methods which involve enzymatic hydrolysis, Grignard chemical degradation, and chromatography analysis. A set of NMR data acquisition parameters and processing methods had proven their excellent versatility and applicability on various types of oils and fats, with systematic error of 1.0 mol%. It was found that there are discrepancies between the regiospecific analysis results obtained by the current method and by conventional methods. Probable acyl migration occurring in the hydrolysis process in conventional methods is a noted problem. As the current ¹³C NMR method is a direct measurement and no hydrolysis of the sample is needed, acyl migration during the analysis is eliminated. As a result, the saturation level is always higher at sn‐1, 3 positions and lower at sn‐2 position in TAG structure of oils in the regiospecific data obtained from the current ¹³C NMR than that from conventional methods. In the absence of laborious chemical derivatization, this method is simple, accurate, and user‐friendly for researchers, especially for nutritionists to support their nutritional studies from the perspective of positional FAC of edible oils and fats.     

Dünnschicht-chromatographische Untersuchung oxydierter Fette und Öle

Thin-Layer Chromatographic Analysis of Oxidized Fats and Oils The oxidation stage of fats and oils can be estimated rapidly with the help of silica gel or aluminium oxide thin-layer chromatography. The presence of different oxidation products in the chromatographically separated fractions was examined by chemical and spectrophotometric methods. The quantitative portion of each fraction, after elution, was determined with the help of hydroxamic acid method. The suggested method is suitable for pure fats and fat containing foodstuffs.     

Diet and lipoprotein oxidation: Analysis of oxidized triacylglycerols in pig lipoproteins

Oxidized lipoproteins have a recognized role in atherogenesis, but molecular-level research on oxidized lipids in lipoproteins and the effect of diet on these molecules have been limited. In the present study, the effects of three sunflower seed oil diets differing in oxidation levels (PV in oils 1, 84, and 223 mequiv O₂/kg) on lipoprotein lipid oxidation in growing pigs were investigated. The emphasis was on the investigation of oxidized TAG molecules found in chylomicrons and VLDL. A method based on RP-HPLC and electrospray ionization-MS was used for the analysis of oxidized TAG molecules. The baseline diene conjugation method was used for the estimation of in vivo levels of lipoprotein lipid oxidation. Several oxidized TAG structures were found in the samples. These products consisted of TAG molecules with a hydroxy, an epoxy, or a keto group attached to a FA, and of TAG molecules containing an aldehyde structure derived from a FA. The lipoprotein lipids and TAG were more oxidized in the pigs fed on the most oxidized oil compared with those fed on nonoxidized oil. Oxidation of dietary fat was reflected in the lipoprotein oxidation. New, detailed information on oxidized TAG molecules of chylomicrons and VLDL was obtained.     

Glycidol and 3-MCPD Analysis Methods for Mono- and Diglycerides

Distilled monoglycerides (DMG) and mono-di-glycerides (MDG) are commonly used as emulsifiers in various processed foods, e.g., bread, margarine, and ice cream. DMG and MDG are derived from triacylglyceride (TAG) oils, and thus it is speculated that the harmful substances glycidol and 3-monochloropropane-1,2-diol (MCPD) or their esters can also appear in DMG and MDG as they do in edible oil. However, present analysis methods, often developed for MCPD esters and glycidyl esters in TAG oils are not suitable for many DMG and MDG products. Dissolution of the DMG and MDG is the main problem. In this work a method for quantifying content of glycidol esters (GE) and 3-MCPD using an indirect method quantifying the compounds with GC-MS has been tested. The development has been developed based on the American Oil Chemists' Society (AOCS) Cd 29c method including the modifications implemented by Axel Semrau in the automated procedure for triglycerides. With the proposed procedure it is shown that the new analysis method produces valid results in the range 1–10 ppm, and acceptable results at 0.5 ppm for both 3-MCPD and glycidol. The method is an important part of providing safe and healthy emulsifier improved food products to consumers in European Commission and the rest of the world. Practical Applications: The European Commission (EU) has requested the emulsifier industry to supply data for GE and MCPD content as a first step in making legislation for maximum content as in edible oils and fats. However, there is no analysis method for emulsifiers (e.g., mono- and diglycerides). This work is a contribution to development of such an analysis method.     

The influence of triacylglycerol structure on the oxidative stability of polyunsaturated oils

There is a growing trend in the use of unsaturated oils in food products and applications. This stems from mounting scientific evidence and increasing consumer awareness of detrimental health effects of dietary saturated fats and trans fats. A major problem with unsaturated oils is that they oxidise very readily forming compounds that impart off‐flavours to food. Susceptibility of oils to oxidation is often discussed in terms of the degree of unsaturation in the component fatty acids. However, the way in which the unsaturated fatty acids are located within the triacylglycerol molecules (positional distribution) can also influence oxidative stability. This paper reviews the literature on the subject.     

Organogels: An Alternative Edible Oil-Structuring Method

Structuring liquid oils has become an active area of research in the past decade, mainly due to pressures to reduce saturated fat intake and eliminate trans fats from our diets. However, replacing hard fats with liquid oil can lead to major changes in the quality of food products. Recent strategies to impart solid-fat functionality to liquid oils include the addition of unusual compounds to oil, leading to its gelation. These include small-molecule organogelators such as phytosterols and 12-hydroxystearic acid, which self-assemble into crystalline fibers which trap oil. Other crystalline additives include waxes, ceramides, monoacylglycerides, and other surfactants. Recently, the polymer ethyl cellulose was reported to form a polymer gel in triacylglyceride (TAG) oils. Other non-conventional strategies also include the formation of protein-stabilized cellular solids with oil trapped within the cells. In this review, we summarize the research on each one of these components in order to provide a comprehensive overview of the state of the area in oleogel research and provide future perspectives.     

Liquid Chromatography–Light Scattering Detector–Mass Spectrometric Analysis of Digested Oxidized Rapeseed Oil

Rapeseed oil was oxidized chemically and thermally to produce two distinct oxidized oils. These oils, along with unoxidized oils, were subjected to an artificial digestion model to simulate the digestive processes in humans. Lipid digestion involves lipases that break down the intact triacylglycerol (TAG) molecules first to diacylglycerols, and eventually to sn-2-monoacylglycerols (MAG) and free fatty acids. A high performance liquid chromatography-evaporative light scattering detector-electrospray ionization-mass spectrometric (HPLC–ELSD–ESI–MS) method was developed to monitor the lipolysis and the presence of oxidized lipids. The HPLC–ELSD–ESI–MS analysis enabled the separation and detection of nearly all the lipid species present in the sample after TAG hydrolysis. The HPLC–MS analyses of digestion products revealed that oxidized triacylglycerols are hydrolyzed by the digestive enzymes in a manner similar to that of native, unoxidized molecules. Significant amounts of sn-1(3)-MAG were found in all the samples after lipolysis, however, more of these were found in unoxidized rapeseed oil samples than in the oxidized oils. Several oxidized molecules were identified with the aid of synthesized oxylipids. This novel method is scalable to small-scale preparative fractionation of oxidized lipid molecules from a complex digestion sample. Also, the fingerprint-like, diagnostic, MS profiles of oxidized oils, reference compounds, and digestion products may be a great aid in comprehensive analysis of lipid oxidation and lipolysis.     

Analysis of traces of anionic detergents in oils and fats

A method to analyze oils and fats for anionic detergents, mainly sodium lauryl sulphate (NaLS), has been developed. After extracting the detergent from the oil, a chloroform-soluble complex with methylene blue is formed, and the concentration of this complex is determined spectrophotometrically. The method was found suitable for oils and fats containing 0.05 to 5.0 mg NaLS per kg. The analysis can only be used to assess fully refined oils and fats because partly refined and commercially available products may contain minor components and emulsifiers also solubilizing methylene blue into chloroform.     

Oxidative Stability of Lipids by Means of EPR Spectroscopy and Chemiluminescence

The aim of this study was to investigate the oxidation of selected vegetable oils (CLSO, CCSO, CBO) at accelerated oxidation rates. Several seldom used analytical methods were applied including electron paramagnetic resonance (EPR), spin trapping with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), Fe²⁺-induced chemiluminescence, Rancimat tests, and the determination of conjugated diens at λ = 233 nm. The antioxidative properties of POBN and DMPO were also investigated. The time required for each method was determined. EPR spectrometry of trapped radicals generated during oxidation turned out to be the fastest method to determine oxidative stability. Chemiluminometric determination of oxidation kinetics showed that POBN has a very strong anti-oxidative potential: it significantly (by 160–277%) lengthened the time to the chemiluminescence peak, as well as the induction time in the Rancimat test (by 110–140%). Photo-oxidation studies showed that superoxide anion radicals are the main factor responsible for the oxidation of lipids in the investigated oils.