Absence of aflatoxin from refined vegetable oils

The present investigation is the first definitive study of the fate of the aflatoxins in vegetable oils undergoing processing. Crude oils, obtained by solvent extraction or by hydraulic pressing of ground moldy peanuts (not suitable for human consumption), contained only small fractions of the aflatoxin originally present in the peanuts; the meals retained the bulk of the aflatoxin. Conventional alkali refining and washing of the oils reduced aflatoxin content to a range of 10 to 14 ppb. The subsequent bleaching operation essentially eliminated aflatoxin from the oils; the concentrations were now less than 1 ppb. The above results were confirmed using corn oils obtained from corn germ deliberately contaminated in the laboratory withAspergillus flavus. The nonfluorescing forms of aflatoxins, capable of being produced during the alkali refining operations, are also absent from the refined vegetable oils; these aflatoxin derivatives are readily converted to their original form on acidification and thereby measurable by fluorescence, if present. Presented in part at the AOCS Meeting, Los Angeles, April 1966.     

Determination of low level trans unsaturation in physically refined vegetable oils by capillary GLC — Results of 3 intercomparison studies

The analytical performance of capillary gas‐liquid chromatographic (GLC) methods for the quantitative determination of trans fatty acids (TFA) in physically refined rapeseed and soybean oils was evaluated by 3 intercomparison studies. The participants were allowed to use their own methodology regarding derivatization and GLC conditions and were not requested to follow a fixed method protocol. However, certain requirements relating to the separation efficiency (chromatographic separation of critical pairs) and the accuracy (validation of the response factors using a certified reference material) of the method(s) applied, had to be fulfilled. All 12 participating laboratories employed fused silica capillary columns coated with cyanopropyl polysiloxane for the separation of fatty acid methyl esters. Analytical precision was sufficient (relative standard deviation for reproducibility 13%) for the quantification of trans isomers occurring at levels >0.1 g/100 g in physically refined vegetable oils, i.e. trans isomers of linolenic acid. For TFA levels <0.1 g/100 g (trans isomers of oleic and linoleic acid) precision dropped sharply (relative standard deviation for reproducibility >30%).     

Titrimetric determination of soap in refined vegetable oils

The low levels of soap encountered in well refined vegetable oils can be determined quickly and accurately in an isopropyl alcohol solution of the oil by a direct titration with .01 N hydrochloric acid in isopropyl alcohol using bromophenol blue as the indicator. Fifty parts per million soap calculated as sodium oleate can be determined with good accuracy and as little as 2 ppm can be detected in refined and bleached soybean oil. Soap in palm oil can be determined using the same solvent and titrant and titrating the sample to pH 5.0.     

Identification of oil mixtures in extracted and refined vegetable oils

Identification of adulteration in mechanically extracted oils or the botanical origin of refined vegetable oil blends can be effectively achieved through the combination of spectroscopic methods and chemometric techniques. Chromatographic methods remain highly relevant but suffer from various limitations which derive from natural compositional variation. Modern multivariate techniques have demonstrated that it is possible to identify patterns and effectively classify unknown samples in both cases. Development of robust analytical methodologies requires however vigorous validation. Spectroscopic methods combined with chemometric techniques lack established validation protocols and this might hinder their use by law enforcement authorities.     

FTIR spectroscopic determination of soap in refined vegetable oils

A new analytical method was developed for the determination of soap in palm and groundnut oils by FTIR spectroscopy. Soap from 0 to 80 mg/kg oil was produced in situ in the oils by adding sodium hydroxide. The FTIR spectroscopy was with a sodium chloride transmission cell, and the partial least-squares statistical method was used to calibrate a model for each oil. The accuracy of the method was comparable to that of AOCS Method Cc17-95, with coefficients of determination (R ²) of 0.98 and 0.98 for both palm and groundnut oils. The standard errors of calibration were 1.84 and 1.36 for the two oils, respectively. The calibration models were cross-validated, and the R ² of cross-validation and standard errors of cross validation were computed. The standard deviation of the difference for repeatability of the FTIR method was better than that for the chemical method used for determining soap in palm and groundnut oils. With its speed and ease of data manipulation by computer software, FTIR spectroscopy is a possible alternative to the standard wet chemical methods for rapid (2 min) and accurate routine determination of soap in chemically refined vegetable oils.     

Studies on antioxidant treatments of crude vegetable oils

Treatments of crude safflowerseed, soybean, sunflowerseed and cottonseed oils with the antioxidant compounds butylated hydroxyanisole (BHA), propyl gallate (PG) and tertiary butylhydroquinone (TBHQ) have been investigated. PG and TBHQ were effective in inhibiting oxidative degradation of the crude oils subjected to long term storage as determined by measurement of peroxide formation in the oils during storage and by determination of AOM and oven (145 F) stabilities of the oils before and after storage. Of particular interest were the oxidative stability characteristics of these oils after they had been stored for relatively long periods in crude form (with and without the antioxidants) and then alkali refined, bleached and deodorized. The data from stability tests on these refined oils indicate that vegetable oils protected with potent antioxidants, such as PG or TBHQ, during storage in the crude form might yield refined, bleached and deodorized oils with somewhat higher initial oxidative stability and with better response to further antioxidant treatment.     

A new analytical procedure to differentiate virgin or non‐refined from refined vegetable fats and oils

The effects of individual steps of industrial refining on the alteration of triacylglycerides (TAG) are reported. The level of dimer triglycerides, normally not present in crude oils, increased after each refining step, especially after steam‐washing and desodorisation. A good correlation between the applied temperatures and dimer triglycerides content was found. The forming of dimer triglycerides starts at 90 °C and increases corresponding to the extension of thermal treatment like normal heating or desodorisation. The data for various types of vegetable oils demonstrate that there is no clear‐cut different tendency to form dimers. Heated oils with different contents of linoleic acid produced nearly the same amount of dimers. Other criteria, like the determination of trans fatty acids, steradienes, or the UV‐absorption, were found not to be appropriate to detect a thermal treatment at temperatures below 150—170 °C. The formation of steradienes mainly depends on the total sterol contents, the percentage of added bleaching earth, and its acidity and moisture. Over 160 commercial vegetable oil samples were analysed to obtain a data range on the content of dimerised triglycerides. Mostly, vegetable oils Iabelled as non‐refined (which may be steam‐washed) did not exceed dimer contents of 0.1%. Virgin vegetable oils did not contain dimers (< 0.05%). The content of dimer triglycerides in vegetable oils was determined by a new method via clean‐up on a short silica gel column, followed by size‐exclusion HPLC with refractive index detection.     

Polycyclic aromatic hydrocarbons in crude and deodorized vegetable oils

The efficiency of the refining process in removing polycyclic aromatic hydrocarbons (PAH) from crude vegetable oils was studied. Samples of the crude oils (coconut, soybean and rapeseed oils) and the corresponding refined, deodorized oil were taken on-line in three Swedish oil refineries and margarine manufacturing plants and analyzed for 20 different PAHs. Of the crude oils, coconut oil had by far the highest PAH levels. However, the PAH levels in the refined coconut oils were very low. This shows that the activated charcoal treatment used for removing PAHs from coconut oil achieves the desired effect. The crude soybean and rapeseed oils contained relatively low, but varying, amounts of PAH. At present these oils are not purified by activated charcoal. Nevertheless, the PAH levels in the refined oils were considerably lower than those in the corresponding crude oils. This probably is due to evaporation of PAH in the deodorization process, where steam is passed through the hot oil under high vacuum. However, deodorization has only a marginal effect on the high molecular PAHs, of which several are classified as carcinogens.     

On the bleaching kinetics of vegetable oils — experimental study and mass transfer‐based interpretation

This study focuses on the systematic investigation of the parameters involved in adsorptive vegetable oil bleaching. These parameters range from the quality of oil and bleaching conditions chosen (e.g. amount and activity of clay, initial water content, temperature, pressure) to the effects of the different reactor systems used (agitated vessel, bubble column) on the kinetics. The study of the latter aims to optimise the type and intensity of power input. The most efficient process was shown to take place in the bubble column reactor. The findings result in a kinetic model for the transport phenomena of the pigments from the oil phase into the clay. The model splits the effects in phenomena due to mass transfer resistances inside and outside of the clay particle. By doing so it is possible to describe the bleaching kinetics in dependence of the amount of clay added and on the size of the external mass transfer resistance, which is influenced by the power input into the reactor. Thus a on model‐based analysis of the effects as well as the optimisation of the bleaching reactor are made possible.     

Characterization and chemometric study of crude and refined oils from table olive by‐products

Table olive processing produces defective fruits and the conditioning operations give rise to solid by‐products which are processed to obtain oil. In this study, the most relevant characteristics of crude oils extracted from table olive by‐products were high average acidity values (4.5%, green olives; 8.1%, ripe olives), ECN42 values of 0.34 (green olives) and 0.10 (ripe olives), while 2‐mono‐palmitin averaged 0.92%. The overall content of sterols was 2257 mg/kg (green olives) and 1746 mg/kg (ripe olives), while the concentration of cholesterol was 36 mg/kg (green olives) and 19 mg/kg (ripe olives). The effect of refining was mainly reflected by a decrease in acidity and sterols. Although most characteristics were in agreement with the established regulation for olive oil, the overall trans fatty acid content, the low apparent β‐sitosterol content, and the relatively high cholesterol content prevented their inclusion into classes of crude or refined lampante or pomace olive oils, not even into the vegetable oil category. Therefore, the oils analyzed should be considered for non‐edible purposes. The physicochemical characteristics used for chemometric discrimination permitted discrimination among types of oils (crude, 100%; physically refined, 90%; chemically refined, 100%), elaboration styles (green and ripe olives, 100%) and cultivars (Gordal, Manzanilla, Hojiblanca and Cacereña, 100%), with the sterol composition being the most useful parameter for discrimination.     

Soap content of some commercially refined oils; Effect of soap on the bleachability of the oils

Journal of the American Oil Chemists' Society - Samples of commercially refined cottonseed and soybean oils, from various points in the centrifugal sodium hydroxide refining process, were...     

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.     

Thermooxidative stability of vegetable oils refined by steam vacuum distillation and by molecular distillation

Semi‐refined rapeseed and sunflower oils after degumming and bleaching were refined by deodorization and deacidification in two ways, i.e., by steam vacuum distillation in the deodorization column Lurgi and by molecular distillation in the wiped‐film evaporator. The oxidative stability of the oils before and after the physical refining has been evaluated using non‐isothermal differential scanning calorimetry. Treatment of the experimental data was carried out by applying a new method based on a non‐Arrhenian temperature function. The results reveal that refining by molecular distillation leads to lower oxidative stability of the oils than refining by steam vacuum distillation. Practical applications : (i) A method for the refining of edible oils by the molecular distillation in the wiped film of a short‐path evaporator is presented and applied. (ii) Oxidative stability of the oils refined by molecular distillation and steam vacuum distillation is compared. It has been found that refining by molecular distillation leads to lower oxidative stability of the oils than refining by steam vacuum distillation. (iii) Experimental data were treated by applying a new method based on a non‐Arrhenian temperature function. The method enables trustworthy predictions of oil stabilities for the application temperatures.     

Comparison of aroma,aroma-active,and phenolic compounds of crude and refined hazelnut oils

Hazelnut (Corylus avellana L.) is an important shelled nut with its pleasant aroma. The refining process causes significant changes in the quality attributes of hazelnut oil. The aim of this study was to assess the aroma, aroma-active, and phenolic compounds of the crude and refined hazelnut oils by using gas chromatography–mass spectrometry (GC–MS), GC–MS-olfactometry (GC–MS-O), and liquid chromatography–mass spectrometry (LC–MS/MS). The antioxidant capacities were also determined by DPPH and ABTS methods. Results showed that terpenes and aldehydes constituted a significant portion of the aroma profile. Refining process dramatically reduced the numbers (from 63 to 25) and amounts of aroma compounds (from 36,769 to 4461 μg/kg). Similarly, the numbers of aroma-active compounds were reduced from 22 to 8 by the refining process. Their flavor dilution factors ranged from 2 to 1024 for crude oil and from 2 to 32 in the refined oil. As of the phenolics, five and two compounds were quantified in the crude and refined oil samples, respectively. In sum, the refining process had a considerable adverse effect on the aroma, aroma-active, and phenolic constituents of the hazelnut oil; hence, the refining process has to be planned with minimal negative effect on its organoleptic properties.