Study On Microwave And Adsorption Technology For Aflatoxin B₁Reduction In Rice

Rice can be easily contaminated by Aspergillus flavus and A. parasiticus because of poormanagement during its production, harvest, storage, and processing, which causes rice aflatoxinpollution. Thus, efficient aflatoxin reduction technology will lead to effective utilization of riceresources in its further processing. Taking aflatoxin B1(AFB1) contaminated rice as raw mate-rial, based on traditional alkali treatment and spraying liquefying treatment, microwave andactivated carbon were used to get AFB1reduced, respectively, and rice protein and starch sugarof non-toxicity and high additional value were prepared. Meanwhile, AFB1degradation prod-ucts were further analyzed, and the safety, functional and structural properties of rice proteinand starch sugar were evaluated to ensure that AFB1reduction technology was safe, effective,and practical.In order to determine the key technical merits and optimum conditions of traditional alkalitreatment, the recovery and purity of rice protein and rice starch were taken as an index, andthree factors, including NaOH concentration, solid-liquid ratio and stirring time were chosen insingle-factor experiment. The results showed that the optimum condition was NaOH concen-tration0.06mol/L, solid-liquid ratio1:8, and stirring time60min. Under this optimum condi-tion, rice protein and rice starch’s recoveries were76.83%and92.32%, and whose purities94.55%and95.81%, respectively. AFB1was reduced partly by traditional alkali treatment. Theresidual concentration of AFB1in rice products of protein and starch was33.91μg/kg and3.47μg/kg, respectively. Based on traditional alkali treatment, microwave-assisted had a significanteffect on AFB1reduction in rice protein. Under the condition of microwave power per unitvolume750W/L treating7min, the degradation rate and residual concentration of AFB1were88.51%and7.33μg/kg, respectively. Furthermore, the degradation feature of AFB1was in linewith the first order dynamic model, and the effect of initial concentration of AFB1on degrada-tion rate constant k was not significant. According to the kinetic model fitting equation, theshortest time (t≤10μg/kg) was prolonged (0.2min to8.6min) with the initial AFB1concentrationincreased (20μg/kg to100μg/kg).AFB1reduction during preparation of starch sugar by activated carbon-assisted sprayingliquefying treatment was investigated. The results showed that AFB1was reduced partly byspraying liquefying treatment, and the critical point of initial AFB1concentration was17.0μg/kg. Model ACJ1with high AFB1-adsorption performance was screened out, and its optimumcondition for AFB1adsorption was pH4.0, temperature45℃and stirring time60min. Theadsorption feature of ACJ1was fit to the Langmuir model, and the regression equation wasy=(0.00114x1.913)/(1+0.000676x1.913). Proven results showed that it was effective in reducing AFB1in starch sugar to make it meet the national standards by using ACJ1in calculating min-imum amount.AFB1degradation products by alkali treatment and microwave-assisted alkali treatmentwere estimated by using UPLC Q-TOF MS detection with MassLynx V4.1analysis. The pre-liminary results inferred that the toxicity of AFB1degradation products was reduced accordingto the molecular structure-toxicity theory (QSAR). Meanwhile, the effect of AFB1and its deg-radation products on HepG2cells was evaluated. The results showed that with AFB1concen-tration increased and time prolonged, toxicity of AFB1in HepG2cells was increased, whichcould reduce the cell survival rate, the content of ROS, ATP, and DNA, and protein expressionextent from P53. Compared with the blank group, AFB1degradation products by microwave-assisted alkali treatment was non-toxic to HepG2cells.Based on the optimized process of AFB1degradation, the functional and structural prop-erties of rice products were evaluated. The results showed the effect of microwave on the re-covery and purity of rice protein was not significant, while the solubility, foamability, oil reten-tion, in-vitro digestibility were improved significantly, emulsification was improved first andthen decreased, while water retention decreased. Furthermore, the total sulfhydryl, disulfidebonds and surface hydrophobicity were improved significantly, while free sulfhydryl decreased.Microwave-assisted treatment might induce some parts of rice protein first gathered to formsoluble macromolecular aggregations, and then these aggregations depolymerized into low mo-lecular protein with microwave treatment time prolonged. On the other hand, activated carbonhad no obvious effects on the quality of starch sugar.