Specific procedure for analysing steryl glucosides in olive oil

Avoiding any kind of oil sample pretreatment, a fraction containing the steryl glucosides (SG) was directly isolated by SPE. This fraction was derivatised and analysed by GC in order to quantify the SG content. The limit of detection of the method was 0.37 mg/kg and the recovery 90%. Additionally, the identity of the SG was confirmed by MS. We applied the procedure to oil samples of different categories and origins indicating that the only SG that could be quantified in olive oil was β‐sitosteryl glucoside, which was present at concentrations not higher than 3.00 mg/kg. Practical applications: Olive oil is of upmost importance from both the nutritional point of view and from the economic repercussion that fraud may have. Among the many parameters required by the EU in order to determine olive oil characteristics, SG are completely overlooked and no specific methodology has been elaborated so far. We have developed a straightforward protocol for the determination of SG in olive oil. This method can be used to provide an additional identity parameter and a new blend indicator. This method is fast, cheap and easy to perform. Besides, it has a great potential for automation which would allow its routine application. The possibility of applying the procedure to study vegetable oils used in the biodiesel industry is also pointed out.     

Novel Method for the Synthesis of Cholesteryl Glucosides starting from Disaccharides

Steryl glucosides (SG) and acylated steryl glucosides (ASG) are natural components of plant cell membranes and present in different concentrations in various plant foods. Currently, their positive effects on human health are under investigation. The present work presents a new and efficient synthesis method for cholesteryl glucosides starting from disaccharides. A five‐step synthesis protocol is done to obtain the desired product in 35% overall yield. In the first step, the hydroxy groups of the starting material sucrose are protected using benzyl ethers. After the subsequent acidic hydrolysis the obtained pyranosyl moiety of the disaccharide is transformed to its trichloroacetimidate derivative. Next, the formation of the glycosidic bond to cholesterol is performed and catalytic transfer hydrogenation in order to remove the protecting groups leads to the desired product. In this context, APCI‐MS‐TOF has turned out to be an excellent analytical tool for the high sensitive analysis of SG as well as intermediates. Practical Applications: Due to the comparatively high amounts of SG and ASG in seeds and oils, not only the food industry but also in biodiesel production, these natural compounds are of increasing interest. However, analysis of the compounds is difficult, commercially available pure standard materials are costly and their synthesis often requires time‐consuming work‐up procedures. The described preparation method allows the synthesis of cholesteryl glucosides which can be used as reference or standard material for the quantitative analysis of phytosteryl glucosides in plant derived samples. The general synthesis method could be also applied to other SG and ASG derivatives. Cholesteryl glucosides are synthesized using a new and efficient five‐step synthesis protocol starting from disaccharides. The preparation method provides products with good overall yield and high purity and, therefore, the synthesized glucosides can be used as reference or standard material for the quantitative analysis of phytosteryl glucosides in plant derived samples. APCI‐MS‐TOF is extensively used as analytical tool for the sensitive analysis of cholesteryl glucosides as well as intermediates.     

A Fluorometric Enzymatic Assay for Quantification of Steryl Glucosides in Biodiesel

Steryl glucosides (SG) are common contaminants in biodiesel that form precipitates, which form and cause problems due to fouling during transport and storage. Therefore, their quantification is necessary to assess the quality of this fuel. The methods currently available for SG analysis require expensive instrumentation, need a previous concentration step by solid‐phase extraction (SPE) or are of limited use for the quantitative assessment. We developed an enzymatic method for SG quantification in biodiesel samples based on the hydrolysis of the glucoside catalyzed by a broadly specific beta glucosidase and the subsequent determination of the glucose released by the reaction. The method is non‐expensive, sensitive and was adapted to 96‐well format fluorescence plate reader, making it useful for the parallel assay of multiple samples. The enzymatic assay presented here represent a valuable tool for both quality control and the development of improved biodiesel production and purification procedures.     

The Identification and Quantification of Steryl Glucosides in Precipitates from Commercial Biodiesel

There have been several discoveries of unexpected precipitates in manufacturing facilities, transport vessels, and storage tanks containing commercial biodiesel. In some cases these have been formed during storage at temperatures above the cloud point of the fuel. High performance liquid chromatography (HPLC) and mass spectrometry (MS) methods were applied to 24 field receipt samples of solids from such biodiesels. The analyses revealed the presence of steryl glucosides (SG), common phytosterols (plant sterol) found in crude soybean oil and many other plant materials, in these biodiesel precipitates. Quantitative analysis of the solids revealed SG concentrations as high as 68 wt% of the provided material (which had not been previously washed with solvent to remove entrained biodiesel). In some samples no SG were present. In others they constituted all of the non-biodiesel material present. Monacylglycerols and diacylglycerols, the products of incomplete transesterification of triacylglycerols, were also present in some samples. The normal phase and reverse phase methods described in this report could be used to analyze SG quantitatively from biodiesel precipitates with an HPLC instrument equipped with either an evaporative light-scattering detector (ELSD) or a more common UV detector operating at 205 nm. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Fractionation of Canola Biodiesel Sediment for Quantification of Steryl Glucosides with HPLC/ELSD

Steryl glucosides (SG) and other trace contaminants in biodiesel may cause filter plugging and engine performance issues, most notably in temperate regions that experience low temperatures. While sediments have been characterized from palm, soybean, and European rapeseed biodiesel, identification of the causative agents and sediment components derived from North American canola (Brassica napus) feedstocks is lacking. Analytic methods used to quantify sediment constituents are time consuming and sample heterogeneity may lead to decreased lab precision. The objectives of this research were to develop a method to fractionate biodiesel sediment in order to confirm and quantify the presence of SG in canola biodiesel. A reverse phase HPLC method with evaporative light scattering detection was modified to confirm the presence of SG from sediments collected at three North American canola biodiesel processing facilities. SG was confirmed in two of three sediment samples where 25.1 and 9.5 wt% of total sediment was SG. FTIR spectroscopy confirmed the presence of SG and provided a rapid method for qualitative confirmation of sediment composition. A third sediment had no detectable SG, but contained a clay filter aide as confirmed by ATR-FTIR spectroscopy.     

Identification and Occurrence of Steryl Glucosides in Palm and Soy Biodiesel

A problem of excessive sedimentation was detected in soy and palm biodiesel, preventing the product from complying with requirements on contamination/filterability. The objective of the study was to determine the nature of the sediment by different analytical techniques and to obtain data on the typical range of its components in industrially produced biodiesel samples. The sediment was investigated and the appearance of haze is linked to the presence of free steryl glucosides (FSG) above a certain concentration. This paper focuses on the original analytical approach, taking into account particular physical properties of FSG. Nuclear magnetic resonance and mass spectrometry were used as fast and reliable identification methods, without the need for a prior hydrolysis of the glucosidic bond. A GC method, including optimised sample preparation, was developed for the quantification of the FSG in biodiesel as well as in filter residues. The FSG concentrations in biodiesel produced by different processes ranged between 55 and 275 mg/kg for palm and from not detectable to 158 mg/kg for soy biodiesel.     

Analysis of Sterol Glycosides in Biodiesel and Biodiesel Precipitates

Biodiesel is produced by the transesterification of vegetable oils with short chain alcohols, usually in the presence of an alkali catalyst. Minor components in biodiesel exist as a result of unreacted reagents, by-products, additives, and auto-oxidation products, such as water, free glycerin, bonded glycerin, free fatty acids, catalysts, residual alcohol, unsaponifiable matter (plant sterols, antioxidants, and hydrocarbons), soaps and polymers. The biodiesel properties, such as cold flow properties, acid number, cetane number, and oxidative stability are oftentimes significantly affected by these minor components. Sterol glycosides, as one of the most important minor components in biodiesel, and due to their polarities and limited solubility, can accelerate precipitate formation even at room temperature and possibly block fuel filters. In this paper, reversed phase high-performance liquid chromatography with an Evaporative Light Scattering Detector (ELSD) is evaluated for the analysis of sterol glycoside (SG) content in not only biodiesel precipitates but also in biodiesel. SG was found to be a major component in soy biodiesel precipitates and an SG peak was found in biodiesel after concentration by centrifugation.     

Identification and quantification of steryl glucosides in biodiesel

This paper discusses the nature and the chemical identification of a white, solid and insoluble residue isolated during the production of biodiesel, using palm or soybean oil as starting material. Using different isolation, purification and characterisation techniques, the solid was identified as a mixture of phytosteryl glucosides. A simple method for the quantitative evaluation of steryl glucoside (SG) concentrations in biodiesel samples is presented and discussed. Some preliminary results about the average concentration in biodiesel and about the solubility limits of SG are presented. The final section of this paper is dedicated to the impact of different crude oil refining techniques before the biodiesel synthesis reaction on the final SG concentration in biodiesel.     

Determination of sulfur contents of vegetable and marine oils by ion chromatography and indirect ultraviolet photometry of their combustion products

A simple method for the determination of total sulfur content in vegetable and marine oils is described. The method involves combustion of the oil sample in an oxygen bomb to convert all forms of sulfur to sulfate ions with subsequent determination of the sulfate by ion chromatography and indirect ultraviolet detection. The ultraviolet system described is more sensitive than conductivity detection and enables the method to be applied more widely. Application of the method to a variety of vegetable and marine oils showed the general occurrence of sulfur in fats and oils, albeit often at a low level. Among the samples examined, crude Canola oil had the highest sulfur content (25.0 mg/kg) followed by the marine oils (5.8-15.2 mg/kg) and the non-Cruciferae vegetable oils (2.0-6.1 mg/kg). To whom correspondence should be addressed.     

Comparing Process Efficiency in Reducing Steryl Glucosides in Biodiesel

A significant obstacle to the commercial acceptance of biodiesel is the potential for filter plugging due to precipitates in the fuel. The majority of these precipitates can be attributed to either steryl glucosides (SGs) or monoacylglycerols in biodiesel. A GC–FID method to quantify minor components content in biodiesel is presented. The effectiveness of room temperature and cold soak filtration, adsorbent treatment, centrifuge, and vacuum distillation processes for SG removal was studied. The vacuum distillation process is the most effective method of removing the SG from biodiesel.     

Development of steryl ester analysis for the detection of admixtures of vegetable oils

The steryl ester content and composition of 28 samples from 10 vegetable oil types have been determined by isolation of the steryl esters by high-performance liquid chromatography and analysis by gas chromatography. The oils can be classified into oils with a high content (>4000 mg/kg) of steryl esters (corn and rapeseed); oils with a medium content (1400–2400 mg/kg) of steryl esters (sunflower oil and high-oleic sunflower oil); and oils with a low content (<1200 mg/kg) of steryl esters (safflower, soybean, cottonseed, groundnut, olive, and palm oils). The composition of the steryl ester fraction varies to a greater extent for different oil types than for different varieties of the same oilseed. The developed method is promising for authentication of some oils, and is particularly suitable for detecting admixtures of low levels of corn or rapeseed oils.     

Ozonized vegetable oil as pour point depressant for neat biodiesel

The use of ozonized vegetable oils as pour point depressant for neat biodiesel was evaluated. Ozonized vegetable oils (1-1.5% by weight) were effective in reducing the pour point of biodiesel prepared from sunflower oil, soybean oil and rapeseed oil to −24, −12 and −30 °C, respectively. Cloud point however remained unaffected. In the case of palm oil biodiesel, significant reduction was observed in cloud point but not in pour point. Statistical analyses showed that neat biodiesel and biodiesel treated with ozonized vegetable oils showed no significant difference in other properties including density and viscosity. Although ozonized vegetable oils increase the flash point of biodiesel, the values are still within the limits set by the standards in the US and Europe. Lowest reduction in pour point was observed in cases where the biodiesel and the ozonized samples were prepared from the same vegetable oil. Hence, a correlation may exist between the nature of the biodiesel and ozonized oil. Microscopic analysis at low temperature revealed that ozonized vegetable oil impede agglomeration of biodiesel into network of solidified material giving crystals with sizes around 10 μm.     

Optimization of biodiesel production from edible and non-edible vegetable oils

The non-edible vegetable oils such as Jatropha curcas and Pongamia glabra (karanja) and edible oils such as corn and canola were found to be good viable sources for producing biodiesel. Biodiesel production from different edible and non-edible vegetable oils was compared in order to optimize the biodiesel production process. The analysis of different oil properties, fuel properties and process parameter optimization of non-edible and edible vegetable oils were investigated in detail. A two-step and single-step transesterification process was used to produce biodiesel from high free fatty acid (FFA) non-edible oils and edible vegetable oils, respectively. This process gives yields of about 90-95% for J. curcas, 80-85% for P. glabra, 80-95% for canola, and 85-96% for corn using potassium hydroxide (KOH) as a catalyst. The fuel properties of biodiesel produced were compared with ASTM standards for biodiesel.     

Formation of Insolubles in Palm Oil-, Yellow Grease-, and Soybean Oil-Based Biodiesel Blends After Cold Soaking at 4 °C

The insolubles formed in biodiesel blends can cause operation problems because they can plug the fuel lines and filters. The formation of insolubles in soybean oil (SBO-), yellow grease (YG-), and palm oil (PO-) based biodiesel blends after cold soaking at 4 °C was investigated. PO-based biodiesel blends displayed a much higher time to filter (TTF) and greater insoluble mass, compared to SBO-, and YG-based biodiesel blends. Fourier transform infrared (FTIR) spectra and gas chromatography-flame ionization detector (GC-FID) chromatograms indicated that PO-based biodiesel insolubles can be attributed to monoglycerides, while SBO-based biodiesel insolubles are due to steryl glucosides (SG). A simple analytical method for identification of SG in biodiesel samples was established by GC-FID.     

Determination of Mineral Oil-Saturated Hydrocarbons (MOSH) in Vegetable Oils by Large Scale Off-Line SPE Combined with GC-FID

A method based on an off-line large-scale solid phase extraction (SPE) approach combined with conventional gas chromatographic-flame ionization detection (GC-FID) was developed to determine the mineral oil-saturated hydrocarbons (MOSH) in vegetable oils. A large-scale SPE column loaded with 10 g of activated silica gel impregnated with 1% silver nitrate which was used to retain lipids and olefins in vegetable oils and the MOSH in the oil samples was eluted with hexane. Then 2 μL concentrated solution was splitlessly injected into a common GC-FID instrument. The quantification limit reached 2.5 mg/kg when the MOSH fraction was concentrated to 0.1 mL. The accuracy of this procedure, as assessed by measuring the recoveries from spiked oil samples, was higher than 80%. This procedure was applied to analyze the MOSH in 38 commercial vegetable oils from Chinese market, which was the first survey of mineral oil contaminant in Chinese edible oils. The oil samples contaminated with different levels of MOSH, among which, 15 samples contained no mineral oils and 3 samples were contaminated with more than 50 mg/kg of MOSH. The highest contamination level was found in one of rice oils, in which the concentration of MOSH was up to 713.36 mg/kg. Of the 9 types of oils analyzed, camellia oil contained MOSH ranging between 6.76 and 78.49 mg/kg, averaging 46.72 mg/kg, indicating a higher contamination level than other types of oils. The results suggested that it is necessary to routinely detect mineral oil contamination in vegetable oils for food safety.     

A Quantitative Method of Analysis for Sterol Glycosides in Biodiesel and FAME Using GC-FID

Sterol glycosides (SG) are known to cause filter blocking problems in biodiesel use. The extraction and quantitative analysis of SG is difficult due to its low problematic concentration and its compatibility with biodiesel. The purpose of this study is to develop a method to quantify SG in FAME and biodiesel using gas chromatography and other equipment found in laboratories performing routine biodiesel analyses. SG was isolated from FAME using n‐dodecane, acidification and cold soaking, followed by cold centrifugation at ?8 to ?15 °C. The solids obtained were further separated by phase partition with a Folch wash, followed by a final n‐dodecane rinse. This solution was analyzed by GC‐FID using the operating conditions outlined in ASTM D6584. A calibration curve for SG was produced and a first order fit gave a value of r² = 0.992. Reproducibility tests were performed on soybean FAME and B100 canola biodiesel samples spiked with SG. The recovery of SG by the new method was found to be 99 % for soy FAME with a standard deviation of 0.7 and 100 % for B100 canola with a standard deviation of 3.5 %. The reproducibility based on two standard deviations of the predicted concentration for all 12 spiked samples studied in this work was 2.4 ppm.     

Relationships derived from physical properties of vegetable oil and biodiesel fuels

The aim of this study was to estimate mathematical relationships between higher heating value (HHV) and viscosity, density or flash point measurements of various biodiesel fuels. The HHV is an important property defining the energy content and thereby efficiency of fuels, such as vegetable oils and biodiesels. The biodiesels were characterized for their physical and main fuel properties including viscosity, density, flash point and higher heating value. The viscosities of biodiesels (2.8–5.1 mm²/s or cSt at 311 K) were much less than those of pure oils (23–53 mm²/s at 311 K), and their HHVs of approximately 41 MJ/kg were 10% less than those of petrodiesel fules (～46 MJ/kg). Compared to No. 2 diesel fuel, all of the vegetable oil methyl esters were slightly viscous. The density and flash point values of vegetable oil methyl esters are highly lower than those of vegetable oils. The HHVs of vegetable oils and their biodiesels were measured and correlated using linear least square regression analysis. There is high regression between viscosity and higher heating value for vegetable oil and biodiesel samples. An increase in density from 848 to 885 g/L for biodiesels increases the viscosity from 2.8 to 5.1 cSt and the increases are highly regular. There is high regression between density and viscosity values vegetable oil methyl esters. The relationships between viscosity and flash point for vegetable oil methyl esters are considerably regular.     

The determination of light petroleum residues in refined oils and fats

A rapid, direct injection gas liquid chromatographic (GLC) method for determining residual light petroleum in edible vegetable oils has been developed. The response is linear at levels between 0.05–0.5 mg hexane/kg oil. A sample containing 0.2 mg hexane/kg oil was analyzed for repeatability, giving a standard deviation of 0.008 mg/kg, equivalent to a coefficient of variation of 4%. Separation of pentane, hexane, heptane, octane and decane was obtained by this method. A survey of 23 samples of freshly refined vegetable oils obtained from 13 U.K. refiners in 1981 showed that these all contained less than 0.05 mg hexane/kg oil.     

Determination of Acylglycerols and Glycerol in Castor:Soybean Biodiesel Blend Produced by a Base/Acid-Catalyzed Process

This paper describes the production of the methyl biodiesel blend of hydroxylated vegetable (castor oil) and soybean oils by a base/acid‐catalyzed process and the first simultaneous determination by gas chromatography of the levels of total and free glycerol, mono‐, di‐ and triacylglycerols based on the standard method ASTM D 6584. Best results were observed for transesterification carried out in 6:1 (methanol:oil), sodium hydroxide 1 % w/w at 60 °C for 1.5 h. The analytical method not only produced curves with good linearity, but also had a coefficient of determination (r²) above 0.997 and accuracy between 70 and 141 % at relative standard deviations (RSD) lower than 10 %. The matrix effect (ME) was investigated and only diolein was found to have a significant matrix effect. The method was robust when applied to different chemical compositions of biodiesel. Results showed that the acid value and the contents of mono‐, di‐, and triacylglycerols, total and free glycerol were within the limits set by standardized methods and that biodiesel may be produced from soybean and castor oil blends.     

Transesterification of vegetable oil to biodiesel fuel using alkaline catalyst

Biodiesel is gaining more and more importance as an attractive fuel due to the depleting fossil fuel resources. Chemically biodiesel is monoalkyl esters of long chain fatty acids derived from renewable feed stock like vegetable oils and animal fats. It is produced by transesterification in which, oil or fat is reacted with a monohydric alcohol in presence of a catalyst to give the corresponding monoalkyl esters. This article reports experimental data on the production of fatty acid methyl esters from vegetable oils, soybean and cottonseed oils using sodium hydroxide as alkaline catalyst. The variables affecting the yield and characteristics of the biodiesel produced from these vegetable oils were studied. The variables investigated were reaction time (1-3 h), catalyst concentration (0.5-1.5 w/wt%), and oil-to-methanol molar ratio (1:3-1:9). From the obtained results, the best yield percentage was obtained using a methanol/oil molar ratio of 6:1, sodium hydroxide as catalyst (1%) and 60 ± 1 °C temperature for 1 h. The yield of the fatty acid methyl ester (FAME) was determined according to HPLC. The composition of the FAME was determined according to gas chromatography. The biodiesel samples were physicochemically characterized. From the results it was clear that the produced biodiesel fuel was within the recommended standards of biodiesel fuel.