2. Materials and Methods
2.2. Microwave Frying Experiments
Microwave frying was performed in microwave oven (Panasonics, Model NN-GT353M, Panasonic Asia Pacific, Panasonic Malaysia Sdn Bhd). Three power levels (high at 800 W, medium at 400 W, and low at 200 W) were used to obtain initial frying temperatures of 180±1, 170±1 and 160± 1°C, respectively. The temperatures of the oils inside the microwave cavity were checked with an optical fiber temperature sensor from OPSens. Power levels were determined by an IMPI 2-L test. Microwave frying was performed in a container containing 300 mL of oil. Room temperature (25±3.0°C) oil was first heated for 8 min to 180 ± 1.0°C at the high power of the microwave oven. The microwave frying potato/oil ratio was maintained at 1:20 (w / v). Four potato slices with an average weight of 15.0 ± 1.5 g were inserted in hot oil at a specific microwave power and frying time of 30, 60, 90, 120, or 150 s. The power of the microwave oven was turned off, and the potato chips were removed, blotted with paper towels, and allowed to cool to room temperature before samples preparation.
2.3. Determination of Acrylamide Content
For sample preparation, potato chips were first minced, and 4 ± 0.1 g was weighed into a 50 ml polypropylene tube. Hexane (20 mL) was added, and the tube was vortexed for 3 min and centrifuged at 5000 rpm for 5 min to remove fat. Ultra-pure water (10 mL) and acetonitrile (10 mL) were added to the tubes and shaken vigorously for 3 min, followed by centrifugation at 5000 rpm for 5 min. A 3 mL aliquot of the supernatant was cleaned-up by solid phase extraction “SPE”. The silica gel cartridges were conditioned with (3 mL) of methanol and (3 mL) of water before loading with (3 mL) of filtered supernatant. The samples were then eluted with (1.0 mL) of ultra-pure water. The samples were further purified by SPE. The purified eluent from was subjected to HPLC analysis.
2.4. Apparatus and Chromatographic Conditions
Chromatographic separation was performed on a module 2695 equipped with a Waters 2489 liquid chromatographic system dual-wavelength UV Vis detector, (with detection at 202 nm) and an injector with a 20 µL loop volume. Empower software was applied for data collecting and processing. A Phenomenex C18 reverse-phase (RP) column (250 mm x 4.6 mm i.d. 5µ) was used for separation. The mobile phase consisted of a mixture of acetonitrile and water (pH 3.5 adjusted with orthophosphoric acid) (20:80 v/v) at a flow rate of 0.8 mL / min with detection at 202 nm. The mobile phase was filtered through a 0.2 µm membrane filter and degassed. The injection volume of 20 µL was performed triplicated. The analysis was performed at ambient temperature.
2.5. Statistical Analysis
All experiments and measurements were performed in triplicate (n=3). Both the means and standard deviations (SD) were calculated using MINITAB (version 14.0, Minitab Inc.) statistical software. A two-way analysis of variance (ANOVA) with Tukey’s multiple comparisons at (P < 0.05) was performed to assess significance.
3. Results and Discussion
The results in (Table 1) showed that acrylamide formation increased accordingly with time for all temperatures for the microwave-fired potato chips fried in RBD palm olein. When frying potato chips in microwave oven at high temperature (180°C/120 s), acrylamide content was the highest and then the acrylamide formation decreased by ≈89% (from 13230 ppb to 1427 ppb) when temperatures changed from 180 to 170°C at 120 s, and about 90% (from 11423 ppb to 1140 ppb) from 180 to 160°C at 150 s. The European Commission recommendation regarding the acrylamide level in foods set a recommendable level for this toxin in potato chips at 1000 ppb. Of the 30 samples of potato chips analyzed, 40% satisfied this recommendation. The values of acrylamide were higher than those reported in Turkish and Columbian fried food products. Most of the potato chips exhibited very high concentrations of acrylamide compared with concentrations reported in the literature. Ghiasvand and Hajipour observed acrylamide concentration in potato chips of 1592 to 18640 ppb. The acrylamide content differed significantly (P < 0.05) as frying temperatures and frying times. Pedreschi found that a reduction of the frying oil temperature from 190 to 170 or 150°C decreased acrylamide formation in potato chips by 61% (≈5300–2050 ppb) and 66% (≈2050–700 ppb), respectively. Haase reported that by lowering the frying temperature from 185 to 165°C and from 190 to 150°C, it was possible to reduce the acrylamide content in potato chips by half and by two-thirds, respectively. Kita also mentioned that a decrease of approximately 75% (3300–1500 ppb) in acrylamide content of potato chips when reducing the frying oil temperature from 185 to 160°C.
Gertz and Klostermann found a decrease of 85% (1240– 184 ppb) in acrylamide content in French fries when lowering the oil temperature from 185 to 160°C. In addition, there was degradation of acrylamide with a frying time of 60 s at 180°C.
"to be continued in the next part"