| Coix seed(Coix lachryma-jobi L.), as one of the important gramineous plant, is a famous medicinal and edible of special crops in China since ancient time. As a major production area of coix seed, Guizhou has become the biggest industrial produciton and products sales gathering area in China and circumjacent countries and territories. So this industry of coix seed has a large development potential at Guizhou. Then, based on the public concerned about the food security of heavy metal pollution on cereal, this paper is the first time to screen the main production area of coix rice, collected the plow layer soil and coix rice, and analyzed their content of heavy metal and the relationship between the plow layer soil and coix rice. Then, for reveal the changing mechanism of heavy metal during the primary processing of coix rice, product of different processing stages at the same line are collected and analyzed content of heavy metal. Moreover, the polished coix rice and broken coix rice, whice come from the different production lines or different machines, were traced and detected the heavy metal pollution and assessed the dietary risks. The last, three kinds of coix rice oils were compared and assessed the mobility ratio of heavy metal, and three different processing methods were carbon dioxide supercritical digestion method, n-butane subcritical digestion method, and light petroleum soxblet extraction method, respectively. The results showed that:1. The analysis of potential ecological risk of collecting plow layer soil from acquisition point indicated that the potential ecological risk of heavy metal in the soil of A-1, B-1, B-2 and C-3 is relatively high and it's not suitable to grow coix rice(Hg:888.0, 430.9, 887.7 and 416.0); the ecological risk of heavy metal in the soil from acquisition point of A-2, A-3, C-2 and C-5 is relatively low and it's suitable to grow coix rice(Hg:81.92, 66.91, 80.72 and 28.85).2.The assessment of soil quality with the p H of soil indicated that availability of heavy metals in collecting plow layer soil of B-1 from acquisition point is relatively high and it is not suitable to grow coix rice. Availability of heavy metals in collecting plow layer soil of A-1, C-3, C-5 and D-3 from acquisition point is relatively low and it is suitable to grow coix rice.3. The analysis of coix rice seed on the enrichment coefficient of heavy metal in plow layer soil indicated that the enrichment of heavy metal in plow layer soil caused by coix rice seed is mainly Cu and Mn. The heavy metal in plow layer soil caused by sampled coix rice seed is higher in A-1, A-2, A-3, C-1, C-5 and D-3 and slight pollution existed.4. The analysis of the heavy metal in the products from the same production line of coix rice seed indicated that the totally incremental amount of heavy mental is relatively high during the primary processing stage and the amount is between 257.1% and 1513%. Thereinto, the pollution of Cu, Zn and Mn is relatively high in coix rice bran. The incremental amount of As, Pb, Cd and Hg is relatively large but within the safety limit.5. The analysis of the products from primary processing stage of coix rice seed from different machines indicated that coix polished rice and broken rice produced from open semi-automatic polish production line with water washing exhibited diet exposure risk of Cu and Mn while the coix polished rice and broken rice produced from closed automatic polish production line without water washing exhibited less diet exposure risk of only Cu. The difference of diet exposure risk of Cu from two production lines is insignificant. The diet exposure risk of other heavy metals is not detected in As ?Pb?Cd?Zn?Mn and Hg.6. The detection of heavy metal extracted from three technics indicated that the amount of Hg, Cu, Zn and Mn in coix rice bran oil from carbon dioxide supercritical digestion method is relatively low, especially the amount of Cu is significantly lower than other two technics. But the amount of Hg, Zn and Mn from light petroleum soxblet extraction method is relatively higher. The assessment of pollution of all extract oil are within safety limit and the pollution indicator of Cu is relatively high and should attract attention. The mobility ratio of Hg is highest in the coix rice bran cake from three methods(carbon dioxide supercritical digestion method, n-butane subcritical digestion method, and light petroleum soxblet extraction method), the mobility ratio reached 89.36%, 14.47% and 31.91%. And the second highest is Cu, the mobility ratio reached 24.23%, 14.65% and 16.83%. |
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