The oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP) methods were used for the determination of antioxidant capacities (AC) of rapeseed oils at different steps of technological process and olive oils. The mean ORAC and FRAP results obtained for rapeseed oils (1,106-160 and 552-95.6 lmol TE/100 g) were higher than for olive oils (949-123 and 167-32.1 lmol TE/100 g). Although, FRAP values were lower than ORAC values for all studied oils, there is a linear and significant correlation between these two analytical methods (r = 0.9665 and 0.9298, P \ 0.0005) for rapeseed and olive oils, respectively). Also, total phenolic compounds in rapeseed oils and olives correlated with antioxidant capacities (correlation coefficient ranged between 0.9470 and 0.8049). The refining process of rapeseed oils decreased the total phenolics content and antioxidant capacities by about 80%.

No abstract

Laboratory-scale treatments of canola oils similar to deodorization were carried out by applying the following conditions: reduced pressure with nitrogen or steam stripping at different temperatures ranging from 210 to 270°C for 2-65 h. The formation of the group of trans linolenic acid isomers follows a firstorder reaction and the kinetic constant varies according to the Arrhenius' law. Similar results were observed for the trans isomerization of linoleic acid. Based on these experiments, a mathematical model was developed to describe the isomerization reaction steps occurring in linoleic and linolenic acids during deodorization. The calculated degrees of isomerization are independent of the composition of the oil but related to both time and temperature of deodorization. The degree of isomerization of linolenic acid is unaffected by the decrease of this acid content observed during the deodorization. Deodorization at about 220-230°C appears to be a critical limit beyond which the linolenic isomerization increases very strongly. The newly established model can be a tool for manufacturers to reduce the total trans isomer content of refined oils, and was applied to produce a special selectively isomerized oil for a European Nutritional Project.Paper no. J8867 in JAOCS 76, 73-81 (January 1999).

Kinetics of the formation of trans linoleic acid and trans linolenic acid were compared. Pilot plant-scale tests on canola oils were carried out to validate the laboratory-scale kinetic model of geometrical isomerization of polyunsaturated fatty acids described in our earlier publication. The reliability of the model was confirmed by statistical calculations. Formation of the individual trans linoleic and linolenic acids was studied, as well as the effect of the degree of isomerization on the distribution of the trans fatty acid isomers. Oil samples were deodorized at temperatures from 204 to 230°C from 2 to 86 h. Results showed an increase in the relative percentage of isomerized linolenic and linoleic acid with an increase in either the deodorization time or the temperature. The percentage of trans linoleic acid (compared to the total) after deodorization ranged from <1 to nearly 6%, whereas the percentage of trans linolenic acid ranged from <1 to >65%. Applying this model, the researchers determined the conditions required to produce a specially isomerized oil for a nutritional study. The practical applications of these trials are as follows: (i) the trans fatty acid level of refined oils can be predicted for given deodorization conditions, (ii) the conditions to meet increasingly strict consumer demands concerning the trans isomer content can be calculated, and (iii) the deodorizer design can be characterized by the deviation from the theoretical trans fatty acid content of the deodorized oil.Paper no. J9828 in JAOCS 78, 973-979 (September 2001).

Solid-phase microextraction (SPME) was developed to determine volatile substances from liquid, gas or even solid materials. This technique has been successfully applied for soil, waste water, blood and urine samples, but in spite of its advantages there are still few applications for vegetable oils. SPME is applicable to determine the aroma and other volatile compounds of the oil, which are characteristic to its origin and oxidative status.In this study the sensitivity and selectivity of some commercially available SPME adsorption materials (polydimethylsiloxane, divinylbenzene, carboxen) were compared. The diverse types of stationary phases were investigated by applying standard oils containing volatile substances from 9-90 mg/kg concentrations. SPME fibre was placed into the headspace of an oil sample in a 30-ml headspace vial thermostated at 80 °C for 45 min. The extracted volatile materials were desorbed from the fiber in the injection port of the gas chromatograph at 250 °C. Identification of the extracted compounds is based on pure standards and mass spectra. The reliability of the SPME sampling method was studied by parallel measurements.The 2-cm long fibre coated with divinylbenzene (50 µm) and carboxen (30 µm) proved to be the most appropriate to determine the volatile oxo-materials from vegetable oils. The method was successfully applied to follow up the formation of volatile substances (e.g. hexanal, t-2-hexenal, t-2-heptenal, t-2-octenal, nonanal, t,t-2,4-nonadienal, t-2-nonenal, t-2-decenal, t,c-and t,t-2,4-decadienal, 2-pentylfuran, 1-octen-3-ol) during deep frying in sunflower oil.