Determination And Research On Several Main Contaminations Of Cereals In Jinan

ObjectivesWith the development of the socilty and the increase of living standard, food security is more and more concerned by the public. In recent years, cereal contaminations such as heavy metal pollutions and mycrotoxin contaminations, have caused serious influence. As cereals are the most frequent consumption of food in our daily life, people pay more attention to the security of cereals. Currently, researches about mycotoxins are focused on aflatoxins, while reports of zearalenone in cereals are relatively little. And there are few researches about detecting zearalenone and heavy metals in Jinan. The study is aimed to established an easy effective and quick method to purify sample solutions by dispersive liquid liquid microextraction. The experiment detected zearalenone in cereals by using high performance liquid chromatography-fluorescence detector and heavy metals such as lead, chromium, cadmium and mercury by using atomic absorption spectrophotometry and atomic fluorescence spectrophotometry. Theresearch aimed to evaluate the current situation of cereal contaminations in major supermarkets and markets in Jinan and provide the data for the government and the people.Methods1 Sample collectionCollect cereal samples from major supermarkets and markets of Jinan. Number the collections of samples and sort properly.2 Determination of zearalenone in cereals2.1 Sample preparationCereal samples were finely milled by using a multifunction grinder and were homogenized to achieve representative level. All samples were stored at 4℃ for analysis.10.0g thoroughly homogenized samples were extracted with 50mL of amixture of methanol/water(80:20, v/v) in a ultrasonic cleaner for 30 min. The extracts were filtered through filter paper (Whatman No.44) for the next procedure.2.2 Dispersive liquid-liquid micro-extraction procedureTypically, 100μL [HMIM][PF6] (as extraction solvent) was added to an aliquot of 1.00mL of 80% methanol extract obtained from above(as dispersive solvent). The mixture was then rapidly injected into a lOmL screw-cap glass centrifuge tube with a conical bottom that contained 5mL aqueous solution (pH=3.0). This ternary component system was mixed for 90s with a vortex mixer and a cloudy solution was quickly formed in the test tube. After centrifugation for 5 min at 4500 rpm, the IL phase deposited at the bottom and the upper aqueous phase was removed by a syringe. The sedimentary phase was dried with a gentle nitrogen stream and dissolved with 100 mL acetonitrile. The solution was finally transferred into a small vial and 10.0μL solution was injected into HPLC for the analysis.2.3 Chromatography detectionUsing high performance liquid chromatography to detect zearalenone in cereal samples. The HPLC system (LC-20A, Shimadzu, Japan) consisted of an automatic sample injector, a quaternary pump, a degasser and a fluorescence detector. A HITACHI-C18 column (250×4.6 mm I.D.,5μm) was used for separation at 30 ℃. The mobile phase consisted of acetonitrile and 1% acetic acid (70:30, v/v) with the flow rate of 1.0 mL/min. The toxin exhibits natural fluorescence and the detector wavelengths were set at ex274nm and em460 nm. All injections were performed manually with 20.0μL sample loop. The injection volume was 10.0μL3 Determination of heavy metal pollutions3.1 Samples per-treatmentCereal samples were dried to eliminate water content. Then samples were milled by a multifunction grinder and mixed for the next experiment.3.2Microwave-assisted sample digestion0.1g cereal samples weighted accurately and 1 mL nitric acid were put into the interpolation jar, in the meantime 5mL deionized water and lmL hydrogen peroxide were put into the outer pot. Samples were disposed by microwave digestion system. Transfer the sample solutions and volume to 10mL.3.3 Element detectionLead, chromium, cadmium were determined graphite furnace atomic absorption spectrophotometry, and mercury was determined by atomic fluorescence spectrophotometry.Results1. The method exhibited linearity over a concentration range from 1.00 to 1000 μg/L zearalenone for HPLC analysis with the regression equation y=266.7x+613.7 and correlation coefficient of 0.9998. The limits of detection (LOD, S/N=3) and quantification (LOQ,S/N=10) were 0.3 and 1.0 μg/kg, respectively. Intra-day precision is between 3.1%-4.7%and inter-day precision is between 1.8%-3.6%.2.Lead, chromium, cadmium were determined graphite furnace atomic absorption spectrophotometry:the regression equation of lead was y=0.0356x+0.080,r=0.9991; the regression equation of chromium was y=0.0619x+0.0579,r=0.9980; the regression equation of cadmium was y=0.0633x+0.0167,r=0.9909; and mercury was determined by atomic fluorescence spectrophotometry with the regression equation y=787.5x+54.1,r=0.9960.3.87.6% of cereal samples were contaminated by zearalenone, maize samples were detected out the highest content which reached 39.0 μg/kg, while oat, coix and wheat samples were relatively high which reached respectively 25.3 μg/kg,24.1 ug/kg,22.4 μg/kg.8% of samples were beyond the limit, the rates of oats, maize and wheat samples were respectively 22.2%,14.3% and 13.3%, while rice and coix samples were detected within the limit.4. All kinds of samples were polluted by heavy metals. The over-limit ratio of lead was 0.88%.All kinds of cereal samples were contaminated by chromium, while oat samples and millet samples were most contaminated. The ratio of cadmium was 2.65%,the rice and millet samples were most polluted. And the ratio of mercurywas12.4%, with the maize, wheat and millet samples were contaminated heavily.5.Of all the cereal samples, the average content of lead was 0.0429±0.0276mg/kg, with the chromium0.159±0.131mg/kg,cadmium0.0244±0.0181mg/kg and the mercury was 0.0156±0.00986mg/kg. After the results were analysed, it was found that the P values of chromium and mercury were less than 0.05, which mean that there were difference among cereals on the contaminations of chromium and mercury. Meanwhile, the others can not be proved the differences were statistically significant.Conclusions1.The proposed method was demonstrated to be simple, cheap, quick and highly selective and was successfully applied to the determination of zearalenone in cereals.2.The situations of cereals contaminated by zearalenone in Jinan were in different degrees, while the ratio of maize, wheat and oat samples were relatively high.3.Cereals were contaminated severely by mercury in Jina nand were polluted by the other heavy metals such as lead chromium and cadmium more or less.