Extrusion Degradation Of Aflatoxin B1 And Related Mechanisms

Aflatoxins(AFT) are the secondary metabolites of Aspergillus flavus and Aspergillus parasiticus, among them AFB1 is the most common pollutant with the highest toxicity. AFB1 has been identified as the Group IA human carcinogen by International Agency for Research on Cancer(IARC). Since AFB1 is widely found in contaminated foods and feeds, the World Health Organization has considered the control of AFB1 in foods as one of the important objectives in the management of global public health. The extrusion cooking and extrusion texturization are the new technologies which can degrade AFB1 in foods effectively. However,the mechanisms of the extrusion degradation of AFB1 in cereals and extrusion degradation products of AFB1 were seldom studied. In the study, with brown rice and maize contaminated by AFT as the experimental materials, the degradation effect of AFB1 by the extrusion cooking process was studied. Then, with peanut meal contaminated by AFT as the experimental material, the degradation effect of AFB1 by the extrusion texturization process was studied. The AFB1 degradation effect in the extrusion degradation process was mainly related to extrusion temperature and the moisture content in materials, so thermal degradation effect of AFB1 in solution systems was explored. Moreover, potential mechanisms AFB1 degradation as well as chemical structures and degradation paths of degradation products of AFB1 were investigated. In addition, the toxicity of maize contaminated by AFB1 before and after extrusion processing was assessed in order to provide the theoretic basis for the application of extrusion degradation. Contents of this research and the main results were as follows:(1) The parameters of the extrusion cooking experiments of brown rice and maize contaminated by AFT were optimized. With brown rice contaminated by AFB1 as the experimental material, the ranges of optimized parameters of the extrusion expansion process were obtained as follows: barrel temperature(160-180 �C), feed moisture content(21%-27%),feeding speed(40-60 g/min), and the screw speed(140-180 r/min). With maize contaminated by AFB1 as the experimental material, the ranges of optimized parameters of the extrusioncooking process were obtained as follows: barrel temperature(150-170 �C), moisture content in feed(21%-27%), feeding speed(42-54 g/min), and the screw speed(120-160 r/min).According to Response Surface Methodology(RSM), the optimized extrusion conditions of brown rice were obtained as follows: barrel temperature of 180 �C, feed moisture content of25%, feeding speed of 45 g/min, and screw speed of 172 r/min and the degradation rate of AFB1 in brown rice reached 53.8%. Through the experiments of Response Surface Methodology(RSM), the optimized extrusion conditions of maize were obtained as follows:barrel temperature of 163 �C, feed moisture content of 25%, feeding speed of 48 g/min, and screw speed of 145 r/min and the degradation rate of AFB1 in maize reached 39.6%. The analysis results indicated that barrel temperature and moisture content showed the significant influences on the degradation effect of AFB1.(2) The parameters of the extrusion texturization experiments of peanut meal contaminated by AFT were optimized. With peanut meal contaminated by AFB1 as the experimental material, the ranges of optimized parameters of the extrusion texturization process were obtained as follows: barrel temperature(130-150 �C), feed moisture content(38%-42%), feeding speed(16-20 g/min), and the screw speed(120-160 rpm). Through the experiments of Response Surface Methodology(RSM), the optimized extrusion texturization conditions of peanut meal were obtained as follows: barrel temperature of 150 �C, feed moisture content of 40%, feeding speed of 17 g/min, and screw speed of 152 r/min and the degradation rate of AFB1 in peanut meal reached 77.6%. The experiments indicated that barrel temperature and moisture content showed the significant influences on the degradation effect of AFB1.(3) The degradation products of AFB1 were analyzed by HPLC-Q-TOF-MS. Since the AFB1 content in peanut meal was low, extrusion degradation products of AFB1 were not detected in peanut meal. In order to simplify the study procedure, the pure AFB1 system(the methanol-water solution system) in polyethylene tubes was heated with an electric heater to explore the influences of processing temperature on the degradation rate and degradation products of AFB1. After thermal treatment at 120 �C, thermal degradation effect of 20 mg/L AFB1 in the methanol/water solution was not significant; after thermal treatment at 210�C, the thermal degradation effect was significant and the degradation rate of AFB1 reached 93.8%.The HPLC-Q-TOF-MS analysis results suggested the molecular formulas of 2 thermal degradation products of AFB1 in the methanol-water system: C17H14O7 and C18H16O7. Thermal degradation products of AFB1 were preliminarily evaluated. The structure analysis of the two thermal degradation products indicated that the addition reaction happened on the Furan Ring,thus decreasing the unsaturation degree. The analysis results of quantitative structure-activityrelationship indicated that the double bonds of Furan Ring were the toxic activity structure.Therefore, under the same concentration, the toxicity of the thermal degradation products was lower than original AFB1, indicating that the extrusion process might reduce the toxicity of AFB1.(4) The thermal degradation kinetics of AFB1 in an aqueous solution was studied.Thermal degradation of 200 ?g/L AFB1 was performed in the solutions with different pH values at different temperatures(100 �C, 120 �C, 150 �C, 160 �C and 180 �C). The degradation rate and degradation degree of AFB1 increased with the increases in degradation temperature and time. After 60-min thermal degradation at 100 �C, the degradation rate of AFB1 was lower than 11%. After 60-min thermal degradation at 150 �C in the solutions with different pH values(5, 7 and 9), the degradation rates of AFB1 were respectively 56%, 29%,and 78%. After 60-min thermal degradation at 160 �C in the solutions with different pH values, the degradation rates of AFB1 were higher than 81%. After 60-min thermal degradation at 180 �C, AFB1 was completely degraded. AFB1 was the most stable at pH 7 and the degradation mainly occurred above 150 �C. Thermal degradation kinetics of AFB1 in aqueous solution systems with different pH values(5, 7 and 9) at 120, 150 and 160 �C followed the first-order kinetic model.(5) The safety evaluation of AFB1 degradation products was performed. In vitro cytotoxicity tests of AFB1-contaminated maize samples before and after extrusion degradation were carried out. The original AFB1-contaminated maize significantly inhibited the growth of HepG2 cells. After extrusion degradation, the apoptotic cells in cytotoxicity tests of the AFB1-contaminated maize were decreased. Therefore, the extrusion degradation process can significantly decrease the cell toxicity of AFB1.