Studises On Bioaccessibility And Bioavailability Of Pollutant-cadmium In Cooked Rice

As the main food in the world,rice is the staple food of half of the world's population.Cadmium is one of the most migrating and potentially bioavailable soil elements,and rice is more susceptible to heavy metal cadmium contamination than other grains.A recent dietary study showed that rice accounts for 56%of total dietary cadmium intake in China's general population and accounts for 65%of China's southern population.In the face of the problem of heavy metal cadmium pollution in rice and the potential harm to human health caused by long-term low-dose exposure,it is of great practical significance to conduct scientific dietary exposure assessment.Therefore,this paper studies the bioavailability and bioavailability of cadmium in rice.The main research contents and conclusions are as follows:In this study,the content of cadmium and other pollutants in rice without grinding degree was studied.Finally,rice with DOM = 9%was selected as raw material.The rice sample was prepared by normal-pressure cooking,and an in vitro static digestion model for the cadmium in rice was established based on the classical RIVM in vitro digestion method.The optimal conditions for the model were determined as follows:the initial pH values of the stomach and small intestine were 2.5 and 7.5,respectively;the bile concentration was 20.0 g/L;the trypsin concentration was 6.0 g/L;the stomach was digested for 2 h,Small intestine digestion 2 h.Subsequently,the bioaccessibility of rice samples of three cooking methods(normal-pressure,high-pressure and microwave)was determined using the established in vitro static digestion model.The study found that the bioaccessibility of Cd(36.93 ± 0.48%)was significantly higher than that of high pressure(31.73± 2.82%)and microwave(31.82 ± 0.71%)after digestion in the oral and gastrointestinal phase.The reason is due to the distribution ratio of Cd in liquid chyme:atmospheric rice>microwave rice>high-pressure rice.The in vitro dynamic digestion model was preliminarily established,and the key parameters of the model were determined as follows:the initial pH value of the stomach was 3.0,the pepsin concentration in the "head phase" gastric juice was 2.5 g/L,and the gastric juice flow rate in the "gastrointestinal phase" was at 10.5 mL/min,the number of gastric emptyings was 4,the emptying flow rate was 25 mL/min,the duodenal phase was 10 min,and the intestinal fluid was pumped at 25 mL/min.The small intestine changes according to the time of digestion and emptying,and the creeping speed changes accordingly.Subsequently,the established in vitro dynamic and static digestion models were used to compare the bioaccessibility of cadmium in rice.The results showed that the cadmium bioaccessibility of the static digestion model was significantly higher at different times during the gastrointestinal digestion stage.This is because the time for the mixed reaction of the chyme and the digestive juice is reduced by 75%in the case of gastric emptying 4 times,but the bioavailability of cadmium after dynamic digestion is measured by the time when the chyme and the digestive juice are in contact for an equal period of time.The result of dynamic digestion may be much greater than static digestion.In vivo female rat model was used to study the cadmium in rice by intragastric administration of rice containing contaminant cadmium to rats for 1 h,2 h,4 h,8 h,12 h and 24 h.Distribution,bioavailability,excretion rate and other indicators:The gastric emptying was complete after 4 hours of intragastric administration;the wet weight of duodenal contents was significantly higher than other test points at 1 h after gavage,and then there was no significant difference,but they were all larger than the blank control group.The sputum and the duodenal segment of the intestinal mucosa were combined;the quality of the jejunum + ileum contents was significantly higher after 1 h of gavage,indicating that the chyme in the jejunum + ileum was the largest temporary residence during this time period.Then gradually decreased,there was no significant difference in quality level after?4 h,and there was no significant difference from the blank control group.It is speculated that the combined amount of chyme and intestinal mucosa in the jejunum + ileum is lower than that in the duodenum;urine and feces are produced after 1 h and 4 h of gavage,respectively,and both increase with time.The net content of cadmium in the stomach contents of rats gradually decreased with time,and the changes in the net content of cadmium in duodenum and jejunum + ileum contents were similar,and both increased first and then decreased.The average size of the net content ranged from 104.98 ng to 820.92 ng and 149.43 ng to 726.77 ng,respectively.The cadmium content in the cecal and colon contents showed similar trends,and the average cadmium content was increasing.The range is 74.47 ng-1004.54 ng and 1.28 ng-318.82 ng.The range of cadmium bioavailability based on the stomach wall,duodenal wall,jejunum + ileum wall,cecal wall and colon wall is:0.22?2.60%,1.05?4.67%,2.66?4.03%,0.1?1.72%,0.11?0.66%;bioavailability of blood-based cadmium was significantly greater at 2 h after gavage,0.055 ± 0.026%;followed by cadmium at 4 h,8 h,12 h and 1 h after gavage The bioavailability levels were:0.031 ± 0.023%,0.025± 0.020%,0.016± 0.010%,and 0.008± 0.003%.The net content of cadmium in urine and feces of rats increased with time,and both of them showed significant maximum levels at 24 h,which were 2.87± 1.56 ng and 257.88±17.70 ng,respectively.The excretion rate of feces at all test points was greater than that of urine,indicating that the cadmium in the rice was excreted from the feces more than the urine.The cadmium excretion rate of urine and feces in rats increased significantly with the increase of time after gastric administration,ranging from 0.02%to 0.15%and 3.30%to 14.72%,respectively.The contribution rate of cadmium in the contents of the digestive tract is much larger than that of the corresponding digestive tract wall and urine and feces.During the whole test period,the contribution rate of cadmium in the total digestive tract content increased first and then decreased;the contribution rate of cadmium in the overall digestive tract wall gradually decreased;the overall excretion(ie urine + feces)The contribution rate of cadmium in the process is gradually increasing.After 1 h,2 h,4 h,8 h,12 h,24 h after gavaged,the sites with the highest cadmium contribution rate at each test time were:stomach contents,duodenal contents,jejunum + ileum contents,cecal contents.