Study On The Change Of Elemental Content And Ultrasonic Leaching Process For Cadmium Reduction During The Processing Of Cadmiumexceeding Rice Grains

This study established a method for the determination of calcium,chromium,manganese,iron,copper,zinc and cadmium in rice products by microwave ablation combined with inductively coupled plasma mass spectrometry,and studied the changes of elemental contents during the processing of rice products based on the processing of rice and steamed grain rice,in response to the waste of food resources caused by cadmium contaminated rice that cannot be used rationally.The ultrasonic leaching cadmium reduction process for rice grains was established and optimized,the characteristics of milled rice and product quality before and after ultrasonic leaching were compared,and the enrichment process of cadmium in cadmiumcontaining waste solution was established,with a view to proposing new ideas for the comprehensive treatment and safe utilization of cadmium-contaminated rice grains,and providing necessary data support for the development of new cadmium reduction processes.(1)In order to establish an accurate method for determining the calcium,chromium,manganese,iron,copper,zinc,and cadmium content in rice products using microwave digestion combined with inductively coupled plasma mass spectrometry,the conditions of the inductively coupled plasma emission spectrometer were selected and the sensitivity and interference values of the mass spectrometry were measured.Meanwhile,the results of the determination of spiking recovery rates in different digestion systems in microwave digestion were compared,and the optimum microwave digestion system was selected.The detection method was subjected to methodological verification,and the results showed that the above seven elements exhibited a good correlation within the selected linear range of the elements,and that the method had high accuracy,good repeatability,and strong stability,in accordance with relevant national standards.(2)The variation in element content during the processing of cadmium-exceeding rice was analyzed.In the processing of rice,the hulling,milling,and polishing processes significantly reduced the element content in the rice.In the processing of parboiled rice,soaking,hulling,milling,and polishing processes significantly reduced the element content in the parboiled rice.The impact of milling time on the element content in rice products was also determined,and the results showed that most of the element content in the parboiled rice was significantly lower than that in rice.Correlation analysis of the data showed that calcium,chromium,manganese,iron,copper,zinc,and cadmium were predominantly enriched in the starch layer.The impact of processing rice and parboiled rice on the element content inside the rice was compared,and the results showed that the cadmium reduction rate of parboiled rice processing at 40.89% was better than that of rice processing at 33.36%.(3)The effects of soaking,soaking combined with shaking,and ultrasonic extraction on the cadmium content in rice were compared.The results showed that ultrasonic extraction had the highest cadmium reduction rate.To improve the ultrasonic extraction process for reducing cadmium,the effects of extraction time,ultrasonic power,and extraction temperature on the cadmium content in rice during ultrasonic extraction were analyzed.Based on the results of the single-factor experiments,a three-factor,three-level response surface experiment was designed to optimize the ultrasonic extraction process for reducing cadmium.The results showed that all the factors had a significant effect on the cadmium reduction rate of rice,and their relative impact was extraction time > ultrasonic power > extraction temperature.Combined with the 3D response surface and contour maps,the optimal conditions for reducing cadmium in rice using ultrasonic extraction were determined to be 116 minutes of soaking time,560 W of ultrasonic power,and an extraction temperature of 53 ℃.Under these conditions,the cadmium reduction rate in brown rice reached 38.97%.(4)To clarify the effects of ultrasonic extraction on the milling properties,cadmium content,and quality of de-cadmium brown rice,the effects of ultrasonic extraction on the milling properties,cadmium content during milling,and the quality of brown rice and finished rice were studied.The results showed that after ultrasonic extraction,the cadmium content in the rice reached its lowest value in a shorter milling time,indicating that the ultrasonic extraction process promoted the internal component migration of the rice grains from the inside out.The cadmium content in the finished rice was 0.54 mg/kg,and the comprehensive reduction rate of cadmium reached 57.48% compared with the cadmium-exceeding brown rice.Meanwhile,the ultrasonic extracted samples were easier to mill,which significantly increased the fraction of broken rice.The ultrasonic extraction process also significantly reduced the element content in the brown rice and finished rice.Analysis on the quality of brown rice showed that ultrasonic extraction significantly reduced the fat acid value,crude starch content,and crude protein content of brown rice,but increased the breakage rate.Analysis on the quality of finished rice showed that ultrasonic extraction significantly increased the L,a*,and b* values,hardness,chewiness,adhesiveness,cohesiveness,and recovery of finished rice,but significantly reduced the internal straight-chain starch content,iodine blue value,and rice soup outflow.The overall palatability of rice was improved,indicating the feasibility of the ultrasonic extraction process for cadmium reduction.(5)To reduce environmental pollution and establish a sound processing technology for cadmium-exceeding rice,a concentration process for the wastewater generated from ultrasonic extraction treatment of rice containing cadmium has been studied.The process involves the use of Spirulina to adsorb cadmium from the wastewater.The study investigated the effects of adsorption time,amount of Spirulina added,and adsorption temperature on the adsorption rate.The results showed that all three factors significantly affect the adsorption rate.Therefore,a3-factor,3-level orthogonal experiment was designed to optimize the Spirulina adsorption process.The optimal combination of factors was determined,with the order of their impact on the adsorption rate as follows: amount of Spirulina added > adsorption temperature >adsorption time.The best process parameters were determined to be an adsorption time of 3hours,addition of 2.2 mg of Spirulina,and an adsorption temperature of 50 ℃,resulting in an optimal adsorption rate of 51.48%.Finally,the adsorption kinetics of Spirulina on cadmium in the wastewater were analyzed,and the results showed that the adsorption process followed a quasi-second-order kinetic model and the chemical adsorption process was the main limiting step.