A preliminary study of PCBs, PAHs, pesticides and trace metals contamination in cold-pressed rapeseed oils from conventional and ecological cultivations.

The purpose of this study was to investigate the levels of polycyclic aromatic hydrocarbons [benzo(a)anthracene, chrysene, benzo(b)fluoranthene, and benzo(a)pyrene], polychlorinated biphenyls (6 marker and 12 dioxin-like), pesticides (74 compounds) and heavy metals (Pb, Cd, As, Hg, Fe, Cu), in the cold-pressed rapeseed oils from conventional (RC) and ecological cultivations (RE). Similar level of PAHs, PCBs and heavy metals was found in the investigated cold-pressed oils; moreover, no effect of rapeseeds cultivation practice on the level of pesticide residues was found. Levels of PAHs, PCBs, and pesticides were within EU legislation limits. Concentration of 4 PAHs oscillated between 3.13 and 6.15 µg/kg, concentration of non-dioxin-like PCBs was within 2599.4-8380.8 pg/g range, dioxin-like PCSs levels varied from 310.2 to 819.4 pg/g (0.307-0.780 pg TEQ/g oil). Iron (Fe) and copper (Cu) were prevailing heavy metals found in the studied oils (0.236-1.690 mg/kg range, 0.036-0.062 mg/kg range, respectively). Measured lead (Pb) contents reached (RC1) or were nearly equal to the EU limit of 0.1 mg/kg (RE1 and RE2).

Mechanical hulling and thermal pre-treatment effects on rapeseed oil antioxidant capacity and related lipophilic and hydrophilic bioactive compounds.

In this study, the effect of rapeseed mechanical hulling and thermal pre-treatment by microwaves (from 2 to 10 min with 2-min intervals, 800 W) and roasting (from 20 to 100 min with 20-min intervals, 165 °C) on the content of phytochemicals in the oil was investigated. Results showed that both pre-treatments applied differentiated the oils in terms of the content of bioactive compounds. In general, oils pressed from hulled and thermally pre-treated seeds contained higher content of tocopherols, PC-8 and phytosterols, while oils pressed from non-hulled and pre-processed seeds had significantly higher concentration of polyphenols. Both microwaving and roasting contributed to an increase of antioxidant capacity of studied oils. The increase of radical scavenging activity of oils was seen mainly in hydrophilic fraction of oil, which was highly positively correlated with the amount of canolol formed during seeds heating.

Dehulling and microwave pretreatment effects on the physicochemical composition and antioxidant capacity of virgin rapeseed oil.

The effect of microwave heating (800 W) of whole and dehulled rapeseeds for 2 to 8 min was investigated in order to evaluate the impact of dehulling in conjunction with microwaving on the nutritional value, antioxidant activity and physicochemical properties of virgin rapeseed oil. Control oil produced from dehulled seeds (DRO) had higher amounts of bioactive compounds, such as tocochromanols and phytosterols, lower content of pigments, and higher content of primary and secondary oxidation products compared to oil pressed from whole seeds (WRO). Oils pressed from seeds that had previously undergone thermal treatment demonstrated gradual increase of oxidative stability, radical scavenging activity, moreover microwave treatment to caused darkening of oil, assessed in terms of changes in L*a*b* coordinates as well as browning index. Thermally-induced compositional changes were seen mainly in canolol, phytosterols, and carotenoids content, while only slight increase of tocopherols and phenolics was observed. The most pronounced effect of microwave pretreatment was noted for canolol formation-for 8-min MV exposure canolol quantity was approximately 7- and 23-fold higher, in comparison with control WRO and DRO samples, respectively (increase from 61.39 to 456.04 µg/g, and from 13.39 to 320.44 µg/g).

The effect of microwave pretreatment of seeds on the stability and degradation kinetics of phenolic compounds in rapeseed oil during long-term storage.

Storage stability and degradation kinetics of phenolic compounds in rapeseed oil pressed from microwave treated seeds (0, 2, 4, 6, 8, 10min, 800W) during long-term storage (12months) at a temperature of 20°C was discussed in the current study. The dominant phenolic compound detected in rapeseed oil was canolol, followed by minor amounts of free phenolic acids and sinapine. The most pronounced effect of seeds microwaving was noted for canolol formation - after 10-min exposure the quantity of this compound was approximately 63-fold higher than in control oil. The degradation of phenolics during storage displayed pseudo first-order kinetics. Differences in the initial degradation rate (r0) demonstrated significant impact of the period of seeds microwave exposure on the degradation rates of phenolic compounds. Results of the half-life calculation (t1/2) showed that the storage stability of phenolic compounds was higher in oils produced from microwave treated rapeseeds than in control oil.

Nutritional value of cold-pressed rapeseed oil during long term storage as influenced by the type of packaging material, exposure to light & oxygen and storage temperature.

The effect of various conditions (storage temperature, exposure to light, access of oxygen) and different packaging material (amber glass, amber polyethylene terephthalate) on the nutritional value of cold-pressed rapeseed oil during 12 months of storage was investigated. Quantified quality parameters included: acidity, peroxide value, spectrophotometric indices (K 232 , K 268 ), fatty acid composition, tocopherols and sterols. Storage of oil at 4 °C was found to be most appropriate for maintaining the quality of cold-pressed rapeseed oil. Exposure of oil samples stored at room temperature to light in combination with the access of oxygen caused the most pronounced losses in the total tocopherols (ca. 90-91 % of α-T, and ca. 80-81 % of γ-T), total phytosterols (ca. 15-16 %) and substantial deterioration in oil qualitative properties. Although storage at room temperature is common for use in households, storage of at low temperatures (4 °C) significantly increases the possibility of prolonged shelf life of cold-pressed rapeseed oil.

Influence of impurities in raw material on sensory and physicochemical properties of cold-pressed rapeseedoil produced from conventionally and ecologically grown seeds.

BACKGROUND: The main problem of cold-pressed technology is its low yield and the varying quality of the end product, which is dependent on the quality of the raw material, technological process applied and also on conditions of packaging and storage. The effects of different contents of impurities in rapeseed on the sensory, physicochemical properties and oxidative stability of rapeseed oil produced by cold-pressing were investigated. METHODS: Cold-pressed oil produced from conventionally grown rapeseeds (individual cultivars and industrial seeds) and certified ecological rapeseeds. Quantified quality parameters included the following: the content of impurities, acid value, peroxide value, spectrophotometric indices (K232, K268), oxidative stability determined by the Rancimat test, pheophytin a content, and sensory assessment. RESULTS: The seeds which were homogenous in terms of cultivar contained the lowest level of impurities (up to 1.3%) and differed significantly in this regard from ecological and industrial seeds. It was found that the presence of impurities exerts an adverse effect on the sensory and physicochemical characteristics of the oil. Impurity content exceeding 5% resulted in the appearance of off -flavours, such as woody, strawy and fusty/musty. Furthermore, a positive correlation was found between impurity content and acid value (r = 0.781), peroxide value (r = 0.656), anisidine value (r = 0.645), K232 (r = 0.625), while in the case of oxidative stability, no such correlation was observed. CONCLUSIONS: The type and percentage of seed impurities in the rape crop determines the sensory and physicochemical properties of the cold-pressed oil. It seems advisable, therefore, to minimize the amount of impurities, in order to obtain high-quality cold-pressed rapeseed oil.

Effect of oil flushing with nitrogen on the quality and oxidative stability of coldpressed rapeseed and sunflower oils.

BACKGROUND: Oxidative stability means resistance to oxidation during purchase, processing and storage and is a key quality indicator of edible fats. Oils ought to be stored in dark-glass bottles, at low temperatures  and with no access of light in order to effectively preserve their oxidative stability. Since all vegetable oils contain unsaturated fatty acids that can react with oxygen and deteriorate over time, displacement of oxygen with inert gases may result in a reduction of the rate of oxidation. In the study the effect of oil flushing with nitrogen on the quality and oxidative stability of cold-pressed rapeseed and sunflower oils was determinate. METHODS: Commercial samples of cold-pressed rapeseed and sunflower oils were stabilized by generating anaerobic atmosphere in the bottles by blowing through with nitrogen and generation of a "nitrogen cushion". Oils were tested in accelerated at 63°C and long-term at 20°C storage tests. RESULTS: After 20 days of Schaal oven test, the peroxide value in the flushing with nitrogen rapeseed and sunflower oils was, respectively, 4 and 7 times lower than in the control samples (without nitrogen). In turn, of the long-term storage test (with access of light 20°C), the peroxide value of oil flushing with nitrogen after 6 months of storage was 2.3 to 2.8-fold lower, respectively, than in the control sample. In the oil samples flushed with nitrogen peroxide formation was inhibited, however, as a result of the breakdown of the peroxides already existed in the oil, gradual decrease of the oxidative stability (determined via Rancimat test) was observed along with prolonged storage of oils. CONCLUSIONS: Oil flushing with nitrogen was a very effective way to reduce the changes caused by oxidation in cold-pressed rapeseed and sunflower oil.