| The problem of rice cadmium contamination has raised widespread concern in the society.The processing technology of cadmium removal is an effective way to rationally use the contaminated rice.Nowadays,slow development of de-cadmium processing technology has severely restricted processing and utilization of contaminated rice and caused huge economic losses to the food industry.In this paper,the high-cadmium rice were used as raw materials We optimized the fermentation process for preparing rice beverage to remove cadmium in the rice by fermentation.Besides,the mechanism of removing cadmium by fermentation and the quality indexs of rice beverage were studied.The purpose of this study was to explore technical feasibility of rice beverage prepared from rice by fermentation and mechanism of removing cadmium by fermentation.It provides a theoretical basis for the technology of removing cadmium in the rice.The main research contents and conclusions are as follows:In the preliminary experiment,the glutinous rice with cadmium content of 0.6817 mg/kg was used as raw material.The content of cadmium in rice beverages which were made of glutinous rice were as high as 0.1601 mg/kg,which was far exceeding the national standard.The saccharification conditions,fermentation strains and fermentation conditions in the process of removing cadmium by fermentation were optimized by single-factor experiments and response surface design The optimum processing conditions were:saccharification temperature 70?,saccharification time 2.5 h,and glucoamylase addition amount.0.1%(w/w),yeast inoculum 0.1%(w/w),secondary inoculation time 24 h,yeast secondary inoculation amount 0.05%(w/w),fermentation temperature 35?,fermentation 50 h,The rice beverage was made after filtration,centrifugation and sterilization.The cadmium content of rice beverages was 0.0563 mg/kg,which was far lower than the limit value of cadmium by national standard of 0.1 mg/kg.The utilization ratio of raw materials is 88.23%.The utilization ratio of raw materials was enhanced by 21.49%compared with that of the supernatant before optimization.The alcohol content of the rice beverage was 1.79.The sensory indexes of the rice beverage were well.The migration of cadmium during fermentation process was investigated.Cadmium content and protein content of different components obtained after fermentation,rice residue,centrifugal supernatant and lower sedimentation,were determined.The results showed that distribution of cadmium in the centrifuged supernatant and the lower sedimentary layer was basically the same as that in yeast,and it was presumed that the yeast could adsorb cadmium.The scanning electron microscopy of yeasts showed that the yeasts had the phenomena of aggregation,deformation and adhesion after treatment of Cd2+ solution.The same phenomenon was observed for yeast which was from the process of removing cadmium by fermentation.Even the bacteria were broken.Under normal conditions,the yeast had a smooth surface,full body and regular shape.IR analysis showed that the adsorption of Cd2+ by yeasts was mainly related to-OH,-NH,CH,NH,-COOH,phosphate groups P-OH,P=O,PO43-,and-CN-groups in amine groups.While during the fermentation,C-O,C=O,P-OH,P=O,PO43-and-CN-in amine group mainly particpated in the adsorption of Cd2+.According to the method specified in the national standard,the sensory index,the physicochemical index,and the microorganism index of the rice beverage were measured and analysed.The results showed that the rice beverage was clear and transparent,with rich rice flavor and fermented mellow,and had a harmonious taste.At the same time,the effect of the optimized fermentation technology on the removal of lead and arsenic from rice beverages was studied.The results showed that the process had the effect of removing lead in rice beverage,and the removal rate was reached to 59.56%.Therefore,this study provides systematic and scientific theoretical reference for the processing of heavy metals such as cadmium and lead-contaminated rice. |
PDF Full Text Request