| Be riched in oleic acid, linoleic acid and other unsaturated fatty acids, and contains a lot of nutrients such as vitamin E, phytosterols, etc, maize oil has become one of the important edible oil in our country.However, maize is easily contaminated by mycotoxin, especially zearalenone(ZEN). ZEN is easily enriched in the germ during extracting germ from maize, and which threated the safety of maize oil seriously. The current maximum residue level of ZEN set by the GB2761-2011 ‘limit of mycotoxins in foods' is 60 ?g/kg in wheat, wheat flour, maize and maize flour(grit, flake), but not set limit to the maize germ and maize oil. GB19641-2005 “hygienic standard of oil plants” and GB 2716-2005 “the hygienic standard of edible vegetable oil” set standard limits only to aflatoxin B1, not to ZEN in maize germ and maize oil. The maximum residue level of ZEN set by the EC 1126-2007 is 400 ?g/kg in maize germ and refined maize oil. In view of the fact that our country attaches great importance to food safety in recent years, the Quality control Department has monitoried the ZEN of refined maize oil according to EC 1126-2007.In this thesis, a series of experimental studies were performed about the high pollution risk of ZEN in production of maize oil. The content level of ZEN in maize germ and maize oil were studied. Then the influence of storage on maize germ, maize germ oil quality and ZEN content were studied in order to obtain reasonable storage condition for maize germ. Meanwhile, the influence of oil quality and oil extraction methods on the distribution of ZEN in oil, meal and cake of different maize germs were studied and the optimum oil-extracting condition was determined. The ZEN removal effect of oil refining process on the maize oil were studied and optimal oil-refining conditions for removing of ZEN from maize oil were determined, in order to provide technical basis for the quality and safety production of maize oil.(1) A method of determining ZEN in maize germ and germ oil, the analytes were purified by liquid-liquid partition and analyzed by HPLC-FLD with external standard calibration. The ZEN detectable rates of maize germ and germ oil were 82.89%~84.48%, 81.86%~86.48%, the RSD were 4.36%~6.30%, 3.69%~5.47% respectively. This method could be used for the detection of ZEN in maize germ and oil accurately. Among all the maize germ and oil samples, the ZEN relevance ratio of maize germ was 100% and the ZEN contents of maize germs ranged from 460.55 ?g/kg to 8710.73 ?g/kg. The ZEN contents of all maize oils ranged from 0?g/kg to 8769.22 ?g/kg, the ZEN relevance of edible maize oils was 75% and ZEN contents of two samples were exceed the maximum limit 400 ?g/kg set by EU.(2) Crude oils were extracted from nine maize germs collected from different factories by solvent extraction and hydraulic pressing methods, and the meals and cakes were obtained. The concentrations of ZEN in different maize germs, crude oils, meals and cakes were determined, to study the effects of different oil extract processes on ZEN contents of crude maize oils, meals and cakes. The results showed that the concentrations of ZEN in different maize germs were ranging from 460.84 to 3084.90 ?g/kg, with an average of 1745.64 ?g/kg; the ZEN contents of solvent extracted maize oils and pressing maize oils were 693.78~3993.82 ?g/kg and 1262.40~4313.44 ?g/kg, with an average of 2567.06, 3126.31 ?g/kg, respectively, and that of the meals and cakes were 419.95.09~2690.94 ?g/kg and 514.31~2554.58 ?g/kg, and with an average of 1556.90, 1534.22 ?g/kg, respectively. The ZEN contents of crude maize oil was higher than the same maize germ, while the ZEN contents of the corresponding meal and cake were lower than that of the germ. The mobility of ZEN was high in oil extract processes and the ZEN was enriched to maize oil. Therefore, the quality of maize germ should strictly control, especially the content of ZEN.(3) The influence of storage conditions on the ZEN content of maize germ and germ oil, as well as the influence on the quality of maize germ and germ oil were studied. The results showed, the maize germ with high moisture contents(12%, 18%) were stored at 25 ? with relative humidity of 45%. The ZEN increments of maize germ were not obviously, the average levels were 1054.73 ?g/kg and 1023.82 ?g/kg respectively and higher than maize germ. But the qualities of germ were decreased, the fat contents decreased by 1.21% and 2.74%, and the acid value of crude oil increased to 20.14 mg KOH/g and 43.22 mg KOH/g respectively. Meanwhile the colour of the oil deepened. The maize germs(with moisture contents of 9%)were stored at 25 with different relative humidity(75%, 85% and 95%). The qualities of ?maize germs and oil stored at high relative humidity(85%, 95%) were greatly deteriorated. Till the 30 th day, the fat contents of germ decreased by 1.21% and 2.74%, and the ZEN increments of maize germ were not obviously, the average levels were 1112.40 ?g/kg and 1098.68 ?g/kg respectively. The acid value of crude oil increased to 25.86 mg KOH/g and 42.98 mg KOH/g respectively, meanwhile the colour of the oil deepened and the ZEN content of maize oil was higher than the maize germ. Accordingly, the influence of storage conditions on the qualities of maize germ and germ oil were significant but not notable on the ZEN increment. But in order to ensure the safety storage, reduce security risks of maize germ and maize oil, it still should to control corn germ stored moisture less than 9% and the relative humidity less than 75%.(4) The ZEN removal effects from maize oil of alkali refining and the optimum alkali refining conditions were studied. The result showed that the ZEN removal effects of appropriate alkali refining were remarkable. The order of influence degree of ZEN removal effect was: alkali concentration > ultra-alkali content >alkali refining time > alkali refining temperature. The optimum alkali refining conditions was as follow: the alkali concentration, ultra-alkali content, alkali refining time and alkali refining temperature were 5.11%,0.4%, 20 min and 55 ?, and with that refining condition, the ZEN content of maize oil was decreased from 8153.33 ?g/kg to 438.06 ?g/kg, meanwhile the ZEN removal rate was 94.63%.The crude maize oil which contained ZEN 4253.58?g/kg was alkali-refined with the optimum process conditions. Then the ZEN content was decreased to 121.08 ?g/kg, and the removal rate was 97.15%, which reached the EU standard limit. The high content of ZEN could not reach the qualification only with alkali refining, which was should combine with adsorption and steam distillation.(5) The ZEN removal effect from maize oil of adsorption and steam distillation as well as ZEN contents of different samples took from the same production line of maize oil factory were studied. The result showed that, the ZEN removal effect of absorbents decoloration was limited. With the use of 1% activated clay, attapulgite, activated carbon WY1, activated carbon WY2, general activated carbon or activated carbon Norit, the removal rate of ZEN on crude maize oil were 5.57%, 10.73%, 38.50%, 11.10%, 14.45% and 17.35% respectively. The ZEN removal effect of activated carbon WY1 was better than other adsorbents. Even with the dosage of 2% activated carbon WY1, the ZEN content of crude maize oil was only decreased from 8026.67?g/kg to 4153.77?g/kg, meanwhile, the removal rate of ZEN was 48.25%. The steam distillation on removal effect of ZEN from maize oil was significant. With the deodorization time of 100 min, deodorization temperature from 210 to 270? ?, the residues of ZEN decreased from 4920.32 ?g/kg to 77.24 ?g/kg and the removal rate risen from 36.38% to 99.00%,. With the deodorization time of 100 min, deodorization temperature of 260?, the ZEN content was 122.46 ?g/kg, which reached the EU requirements that the limit of ZEN in edible corn oil was set at 400 ?g/kg. Comprehensive consideration of ZEN removal effect, oil refining loss, energy consumption and nutrients retention, the appropriate steam distillation deodorization process condition was deodorization temperature 250 ?and deodorization time 120 min. The ZEN contents of solvent extraction oil, alkali refined oil, dewaxed oil, bleached oil and deodorized oil were 8433.90, 2383.51, 2474.14, 1821.20, 308.77 ?g/kg, respectively. As the refining process, the ZEN content of maize oil was reduced gradually. At the same time, the ZEN removal effects of alkali-refining and deodorization were better and the effect of decoloration was poorer, which was consistent with the experimental results.Among tested samples, the maize germ and crude maize oil all contained ZEN. The ZEN contents of maize germ and crude oil were 3197.41 ?g/kg and 4269.73 ?g/kg, respectively. The quality changes and ZEN contamination were produced under the poor storage conditions. The ZEN of maize germ was enriched to maize oil by oil extraction process. The removal effects of ZEN were better by alkali refining and steam distillation but pooer by adsorption. The high content of ZEN could be removed from maize oil effectively by alkali-refining, which combined with adsorption and steam distillation. Therefore, proper storage conditions, strictly controlled condition of crude maize oil and reasonable refine condition were necessary to ensure the safety and quality of maize oil. |
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