Researches On Technologies Of Reducing Cadmium In Rice By Lactic Acid Bacteria Fermentation

In recent years, excessive cadmium in rice has become a serious food security problem in China caused by environmental pollution. At present, despite rice variety selection, soil remediation and fertilizer control technologies can reduce the number of excessive cadmium rice in a certain extent, but it is difficult to accomplish the popularization of these technologies in a short time, so excessive cadmium rice will still exist in a certain time. Doing the research on technologies of reducing cadmium in rice was beneficial to prevent excessive cadmium rice as the staple food, to prevent food safety incidents, to expand transformation and utilization ways of excessive cadmium rice, to improve economic benefits of transformation and utilization of excessive cadmium rice and protect the enthusiasm of growing grain for farmers. Excessive cadmium polished rice were selected as raw materials in this paper. When the optimal detection conditions of cadmium in rice were obtained, this paper explored the feasibility of the method of reducing cadmium in rice by lactic acid bacteria fermentation technology, and the fermentation conditions were optimized. And this paper preliminarily investigated the mechanism of reducing cadmium in polished rice by lactic acid bacteria fermentation. Based on this, in order to explore a effectively new technology of reducing cadmium in rice, this paper tried further to carry out study on the technology of reducing cadmium in rice by acid leaching-fermentation. The main research contents and results were as follows.1? The determination of the detection method of cadmium in rice.The study used wet digestion as pretreatment of rice sample and mainly studied the effects of digestion solvents on pretreatment of sample. Then, the content of cadmium in rice was tested by graphite furnace atomic absorption spectrometry. The detection performance of the instrument was adjusted to the best condition by seeking a suitable matrix modifier, ashing temperature and atomization temperature. And the optimal detection conditions were obtained as that:HNO3-HClO4(6:1) was taken as the optimum digestion liquid for digesting rice samples, matrix modifier for NH4H2PO4 g/L, automatic sample 2 ?L), carbonization temperature of 550 ?, atomization temperature of 1800 ?. The results showed that the detection limit, average recovery rate and RSD of this method were 0.3 ?g/kg,101.74% and 2.55%, respectively.2? Study on the technology of reducing cadmium in rice by lactic acid bacteria fermentation.In this part, using cadmium reduction rate as inspection index, mainly studied the process of reducing cadmium in rice by lactic acid bacteria fermentation, and studied and optimized the fermentation conditions. The results showed that the mixed strains of Lactobacillus plantarum and Pediococcus pentosaceus(2:1,v/v) was selected as the suitable fermentation strain, rice powder size was selected as 40 mesh. And the optimum fermentation conditions were obtained with fermentation temperature of 40.8 ?, fermentation time of 23.4 h, the inoculum size of 3%. Under this condition, the verification test demonstrated that the reducing rate of cadmium in polished rice was 85.73%, and the content of cadmium in fermented rice powder was 0.0925 mg/kg and met the national food sanitation standard (0.2 mg/kg).3% The study on mechanism of reducing cadmium in rice by lactic acid bacteria fermentation.On the basis of determination of the optimum conditions of reducing cadmium in rice by lactic acid bacteria fermentation, this part investigated the mechanism of reducing cadmium in polished rice by lactic acid bacteria fermentation through the major fermented products(lactic acid and enzymes). The effects of lactic acid bacteria and their different fermented products on the reducing rate of cadmium and the content of protein in rice were compared and analyzed. And the relationship of protein content and cadmium reducing rate in rice also was studied. The results showed that lactic acid bacteria reducing cadmium in rice by fermentation was mainly related to lactic acid. Not only was lactic acid reducing cadmium in rice related to hydrogen ions of acid, might be related to the molecular structure of lactic acid (lactic acid molecule with alpha hydroxyl and carboxyl functional groups). This study demonstrated that lactic acid can promote protein dissolving out from rice powder. In addition, protein content in rice and cadmium reducing rate had a significant negative correlation. The results indicated that the increasing of cadmium reducing rate in rice with the reduction of protein content. Thus, reducing the content of protein in rice may contribute to the reducing of cadmium.4?Study on acid leaching process of reducing cadmium in rice combined fermentation technology.Based on the discovery of lactic acid being the main reason for reducing cadmium in rice by lactic acid bacteria fermentation, fermentation parameters were fixed, and excessive cadmium rice were soaked in acid for pretreatment before fermented by lactic acid bacteria. Using cadmium reduction rate as inspection index, the effect of acid leaching conditions on the reducing rate of cadmium was studied. The results showed that lactic acid was selected as suitable soaking solution from seven kinds of acids. When leaching time was selected as 12 h, the optimum acid leaching conditions were obtained with leaching temperature of 44.2 ?, acid concentration of 48%(v/v), liquid-solid ratio of 9:1 mL/g by response surface method. Under the optimal conditions, the verification test of the reducing of cadmium was carried out with the result of cadmium reducing ratio of 98.01%, and the content of cadmium in processed rice powder was 0.01289 mg/kg, lower than the national standard limit of 0.2 mg/kg. But the comparative analysis of determination of main metal elements in raw rice powder and processed rice powder found that the technology can effectively reduce harmful heavy metals(Cd?Pb?As?Hg) and also reduce the content of important trace nutrient elements(Mg?Mn?Fe?Cu) in rice significantly.