| ObjectiveBenzo[a]pyrene(Bap) is the most carcinogenic in polycyclic aromatic hydrocarbon compounds(PAHs),which is widely exist in our lives.Acid value is an important marks for evaluating the quality of the oil.Peroxide is an early sign of oxidation degree of cooking oil, Peroxide value is a commonly chemical index which measure the level of rancidity of cooking oil and evaluate whether the oil accord with the country health standard. The evaluation of the three indicators is important on human health. This paper is based on some of the existing research, improved the methods,set up a new method which use no-bond silica gel solid phase extraction column(SPE) to separate the sample and apply high performance liquid chromatography with fluorescence detector to detect the sample.And with this approach to detect the level of benzo[a]pyrene in oil of famous brand, oil extracted by individual workshop and oil with non-brand,no packaging in Jinan.And determining the acid value and peroxide value with reference to national standard method.The purpose is to understand the level of acid value, peroxide value and benzo[a]pyrene in edible oil in Jinan market,and to compare the difference between content in oil of famous brand, oil extracted by individual workshop and oil with non-brand,no packaging.Methods1The measurement method of benzo[a]pyrene in edible oil1.1Sample handling:Accurately weigh2.5g (accurate to0.001g) sample in a 100mL volumetric flask, diluted with hexane constant volume; Activation treatment on silica gel solid phase extraction column, solid phase extraction column first wash with5mL dichloromethane to remove impurities, and after drying, rinse with5mL of hexane to activation of the column.Then take1mL of the sample added in1000mg/6mL silica gel solid phase extraction column, and eluting with hexane and dichloromethane3:1mixture,control the flow rate of1d/s,collect about20mL of the solution, the collection was blew to20-30uL in the conditions of60℃with nitrogen, then naturally dried at room temperature. The residue dissolve in100uL of acetonitrile.1.2Chromatographic conditions:Solid phase extraction-high performance liquid chromatography-fluorescence detection has been application. Shimadzu LC-20AT high performance liquid chromatography, RF-20A fluorescence detector, the SHIMADZU shim-pack VP-ODS (250L×4.6mm,5μm) column were measured. Mobile phase was methanol:water ratio of90:10. Flow rate of lml/min, lOuL of the injection volume, column temperature is35℃, Determination under the conditions of excitation wavelength(Ex)285nm and emission wavelength(Em) of406nm.2Determination of acid value in edible oilAnalytical methods:Mixing the sample, taking3.00g～5.00g placed into a flask, add50mL mixture blend with neutral petroleum ether and ethanol. Shaking the oil to make it dissolved even set into the hot water. When cooled to room temperature, add2to3drops of phenolphthalein indicator solution,and and titrate it with potassium hydroxide standard solution (0.050mol/L). The end point for the micro-red does not fade within0.5min. Recorded dosage of potassium hydroxide standard titrant.3Determination of peroxide value in edible oilsAccurately weigh2.0to5.0g sample into the flask, add50mL of acetic acid-isooctane solution dissolving the sample,even can shake it by covering with a stopper. Then add0.5mL of saturated potassium iodide solution, cover the stopper making it react for1min, continue to shake the flask for at least three times, then immediately add30mL distilled water. Titration the solution with sodium thiosulfate solution, and accompanied by strong stirring, add about0.5ml of starch solution when the yellow almost disappear, and continue titration, Towards the end, dropwise add titrant and continue to shake to make all of the iodine released from the solvent layer. When the blue is disappearance is the end.Results1The results of benzo[a]pyrene determination in the edible oil1.1Benzo[a]pyrene have a good linear relationship within the concentration of0.0330～33.0ng/mL,γ=0.9999. Detection limit of benzo[a]pyrene in the edible oil0.039μg/kg (S/N=3), the recovery percent (REC)of sample was85.8%～90.7%,relative standard deviation(RSD) in one day is2.9%～4.1%, relative standard deviation during the day is3.7%～5.3%.1.2There have71samples in total, oil of famous brand have28scores, oil extracted by individual workshop hace25scores and oil with non-brand,no packaging have18scores. The number of samples detected which contain benzo[a]pyrene is65, the detection rate is91.5%. The ranges of benzo[a]pyrene content is0.039～9.69μg/kg, according to the standard of food prescribed in GB2762-2005, the limit value of benzo[a]pyrene in vegetable oils is10μg/kg,there have no sample exceeded the limit value,but in accordance with the standards of the European Union in2005, the limit value of benzo[a]pyrene in vegetable oils is2μg/kg,31samples have exceeded the limit value,43.7%of the total sample.1.3The content of benzo[a]pyrene in famous brand oil, oil extracted by individual workshop and non-brand,no packaging is different, respectively, the content is1.76±1.88μg/kg,3.33±2.60μg/kg,1.51±1.36μg/kg, average levels of benzopyrene in the market oil is higher than brand oil and self-squeezed oil, the oil which has the highest content of benzo[a]pyrene is in the market of oil; Compare the number of samples of three kinds of oil which the content of benzo[a]pyrene is greater than2μg/kg, brand oil have nine,accounting for32.1%of the total number, market oil have sixteen, accounting for64.0%of the total number of samples, self-squeezed oil have six, accounting for33.3%of the total number of samples;So it comes to a conclusion that the content of benzo[a]pyrene in the market oil is higher than the brand oil and self-squeezed oil. Statistically, compared with brand oil group,there has significant statistically difference between the market oil and brand oil (P<0.05),and there has no significant statistically difference between self-squeezed oil and brand oil.So the conclusion is that the content of benzo[a]pyrene in market oil is higher than the brand oil and self-squeezed oil,the content of benzo[a]pyrene in the brand oil and self-squeezed oil is similar.2The results of acid value determination in the edible oilThe value range of determination of acid value is0.013～6.52mg/g, in accordance with GB2762-2005, acid value limits of vegetable oil is3mg/g,6samples have exceeded the limits, accounting for33.3%of the total number of samples, the sample which exceeded the limits is mainly concentrated in the self-squeezed oil group. The average measured value of the acid value was0.961±0.921mg/g,1.05±0.810mg/g,2.06±1.54mg/g, respectively, self-squeezed oil have the higher acid value. By statistical analysis, compared with brand oil group, there has no significant statistically difference between market oil and brand oil (P>0.05), there has significant statistically difference between the self-squeezed oil and brand oil (P<0.05).So the the conclusion is that the acid value of self-squeezed oil is higher than the brand oil and market oil, the acid value of the brand oil and market oil is similar.3The results of peroxide value determination in the edible oilThe value range of determination of peroxide value is0.005～0.819g/100g, in accordance with GB2762-2005peroxide value limits of vegetable oil is0.25g/100g,32samples of the total exceeded limit value, accounting for45.1%of the total number of samples. Brand oil have twenty,accounting for42.9%o f the total number, market oil have sixteen, accounting for24.0%of the total number of samples, self-squeezed oil have fourteen, accounting for77.8%of the total number of samples; The average measured value of the peroxide value was0.243±0.174g/100g、0.191±0.184g/100g、0.370±0.191g/100g, respectively. By statistical analysis, compared with brand oil group, there has no significant statistically difference between market oil and brand oil (P>0.05), there has significant statistically difference between the self-squeezed oil and brand oil (P<0.05). So the the conclusion is that the peroxide value of self-squeezed oil is higher than the brand oil and market oil, the peroxide value of the brand oil and market oil is similar.ConclusionsIn this paper, pretreatment samples by the non-bonded silica gel extraction column, and apply high performance liquid chromatography with fluorescence detector to detect benzo[a]pyrene of the sample. Detection limit of benzo[a]pyrene in the edible oil0.039μg/kg, the recovery percent (P)of sample was85.8%～90.7%. The experimental method is well separation, sensitivity, accuracy, and reliable, suitable for determination of benzo[a]pyrene in edible oil.Through the determination of benzo [a] pyrene, acid value and peroxide value in edible oil in Jinan, and according to the provisions of GB2762-2005and the EU about the limits of contaminants in foods and hazardous substances control standards,take an investigation of famous brand oil, market oil and self-squeezed oil in Jinan, Shandong Province. Analyzed by statistical software,get the conclusion that the content of benzo[a]pyrene in market oil is higher than the brand oil and self-squeezed oil, acid value and the peroxide value of self-squeezed oil is higher than the brand oil and market oil. |
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