【作者】 王锋；

【导师】 哈益明；

【作者基本信息】 中国农业科学院 ， 生物物理学， 2012， 博士

【摘要】 黄曲霉毒素（Aflatoxins，简写AF）是由黄曲霉菌和寄生曲霉菌等产生的次级代谢产物，其中黄曲霉毒素B₁（AFB₁）是国际癌症研究机构（IARC）界定的ⅠA类强致癌物质，其研究和安全管理日益受到重视。由于AFB₁广泛存在于污染的食品和饲料中，世界卫生组织已将控制食品中AFB₁污染作为全球公共卫生管理的重要目标。电离辐射技术是一种能有效降解食品中AFB₁的新型技术。然而，关于AFB₁在食品中的电离辐射降解机理及其辐解产物的研究鲜有相关报道。本研究按照从简单到复杂的研究思路，以甲醇-水体系、水体系、花生粕中的AFB₁为研究对象阐明了不同介质中AFB₁的辐射降解效果，解析了辐照AFB₁不同体系中的辐解产物结构特性，初步探讨了AFB₁水溶液中辐解产物形成的辐射降解机理。研究结果概述如下：（1）研究证实了射线辐照能有效降解甲醇-水溶液（V：V=60：40）中的AFB₁。结果表明，辐射剂量越大，AFB₁的降解率越高，0.1mg/L的AFB₁溶液在4kGy时降解率已经达到82.4%，6kGy时降解率达到96.3%；试验还证实，初始浓度越低，AFB₁的降解越容易，0.1mg/L的AFB₁溶液在3kGy时降解率58.8%，10mg/L的AFB₁在6kGy时降解率58.8%。（2）以LC-Q-TOF-MS作为研究手段分析检测AFB₁毒素的主要辐解产物，通过不同剂量的辐照处理，在AFB₁甲醇-水体系中共检测到有25个辐解产物，不仅种类多，而且浓度低；利用该仪器获得不同辐解产物的离子碎片的基本信息（分子量和碎片），结合一级、二级质谱提供结构判断的补充信息，研究解析出不同剂量辐照后，AFB₁甲醇-水体系中重复出现的7个主要辐解产物的分子结构信息，其产物分子式分别为C₁₇H₁₄O₇、C₁₆H₁₀O₅、C₁₄H₁₀O₆、C₁₈H₁₆O₈、C₁₆H₁₄O₇、C₁₇H₁₄O₈（a）、C₁₇H₁₄O₈（b）。通过结构解析初步表明，AFB₁的辐照降解遵循自由基反应机制。（3）初步研究评估了AFB₁的主要辐解产物的毒性效应。分析比较辐解产物与AFB₁的结构组成，其中有18个辐解产物的呋喃环双键被加成，与AFB₁的不饱和度相比较都有相应减少。根据定量构效关系分析，呋喃环双键部位是AFB₁的毒性活性结构，也是引发人类原发性肝癌的主要结合部位。因此，根据定量构效关系分析，AFB₁的毒性辐照后经评估可降低约70%。（4）研究证实辐照AFB₁水溶液更容易发生降解，辐照后AFB₁悬浊液变为澄清溶液。由于悬浊液每次与水的接触不一致，导致每次辐照后降解效果有差异，但是总的趋势是辐射剂量越大，降解率越高。20mg/L的AFB₁悬浊液经过两次10kGy辐照后，降解率分别为94.3%和74.9%。与甲醇-水体系相比，AFB₁悬浊液辐照后辐解产物更少，表明辐射水产生的自由基可能是导致AFB₁降解反应的主导因素。利用LC-Q-TOF-MS分析检测，研究获得了AFB₁水溶液体系中4个辐解产物的分子结构信息，其产物分子式分别为C₁₇H₁₄O₇、C₁₇H1₂O₇、C₁₆H₁₂O₇、C₁₆H₁₀O₆。其中只有产物C₁₇H₁₄O₇结构与甲醇-水体系中相同。（5）有关AFB₁水溶液的辐射降解机理的研究，首先设定了不同的气氛屏蔽调控措施，采用N₂饱和、N₂O饱和、N₂饱和+异丙醇、N₂饱和+H₂O₂、N₂饱和+叔丁醇等试验条件，使不同的调控措施出现不同的主导自由基，通过对AFB₁水溶液辐射降解效果的分析和辐射化学产额G值的比较，确定了辐射降解过程中在AFB₁水溶液起主导作用的自由基。各自由基在AFB₁降解过程中的贡献大小依次为：HO₂·，O₂>OH·>e-aq>H·。（6）研究采用食品基质花生中污染AFB₁进行试验，结果表明：花生粕中高浓度的AFB₁仍然能够实现有效辐照降解。20mg/kg的初始浓度经过20kGy辐照后降解率为14.4%，与水、甲醇-水、AFB1固体纯品中AFB1的降解率进行比较后，预测水在AFB1的辐射降解过程中发挥着重要作用。而且研究利用独辟蹊径的方式，在经过优化后的AFB1提取净化步骤后，采用LC-Q-TOF-MS分析搜索前期甲醇-水溶液中出现的25个辐解产物，进行逐一的选择离子检测后，最终在花生粕中检测到2个主要的辐解产物，它们分别是：C₁₆H₁₄O₇（319.0813m/z）和C₁₇H₁₄O₇（331.0821m/z），其产物结构与甲醇-水体系中辐解产物相同。更多还原

【Abstract】 Aflatoxins （AF） is the secondary metabolites formed mainly from the Aspergillusflavus and Aspergillus parasiticus, and the International Agency for Research on Cancer（IARC） has classified aflatoxin Bl（AFB₁） as a Group1A human carcinogen, so theresearch and security management about it has been paid more and more attention. Sinceaflatoxins are widely distributed in food and feed, the World Health Organization hasconsidered the control of AFB₁pollution in food security as an very important goal of theglobal public health management. Ionizing radiation technique （IRT） is a new techniquewhich could degrade AFB₁in food effectively. However, the degradation mechanism ofAFB₁in food and the research about radiolysis products were rarely reported. Thisresearch has been designed from simple to complex and we studied AFB₁in the methanol-water system, water system and peanut meal. The effects of the degradation in differentsystems were stated and radiolysis products of AFB₁in different mediums were studiedrespectively. Thus, we preliminarily discussed the degradation mechanism by irradiation ofAFB₁in water and the results are listed as follows:（1） We confirmed that gamma rays irradiation can depredate AFB₁in water-methanolsystem （V:V=60:40） effectively. Results showed that the greater the radiation dose was, thehigher the degradation rate of AFB₁could be. The degradation rate of AFB₁（0.1mg/L）were over80%with the irradiation dose of4kGy in methanol-water system, anddegradation rate of AFB₁（0.1mg/L） in methanol-water solution reached to96%at6kGy.We have also confirmed that the lower initial concentration of AFB₁was, the easierdegradation of AFB₁could be. The degradation rate of AFB₁in methanol-water solution（0.1mg/L） at3kGy was58.8%, which was approximately consistent with the degradationrate （58.8%） of AFB₁in methanol-water solution （10） mg/L) at6kGy.（2） LC-Q-TOF was used as a tool for detection of radiolysis products. We studied2₅radiolysis products of AFB₁which was produced in methanol-water system at differentirradiation dose. These radiolysis products which have many types and low concentrationswere analyzed by TOF to obtain the basic information of ion fragments （molecular weightand pieces） and then this result was combined with the supplementary information ofstructures by tandem mass spectrum to find structural information of₇radiolysis products(C₁₇H₁₄O₇, C₁₆H₁₀O₅, C₁₄H₁₀O₆, C₁₈H₁₆O8, C₁₆H₁₄O₇, C₁₇H₁₄O8（a）and C₁₇H₁₄O₈（b）) at differentirradiation doses. Through the structure analysis, it was preliminarily showed that theradiation-induced degradation of AFB₁was followed by free radical reaction.（3） We assessed the toxicity of radiolysis products of AFB₁. Comparison study showedthat six out of the seven main radiolysis products had been through addition reactionhappened on the Furan Ring, which led to the reduce of unsaturation. According to theanalysis of quantitative structure-activity relationship, the double bond of Furan Ring is thetoxic activity structure and also the main combination part which can cause primary cancer of humanbeings. Therefore, the toxic of the radiolysis products were lower than AFB₁withthe same concentration.（4） Results showed that the degradation of AFB₁in water solution is much easier, andafter irradiation the turbid liquid became clarified. Because the collision between AFB₁turbid liquid and water was not always homogeneous, irradiation degradation effects can tkeep constant. However, the general trend is that the bigger the radiation dose is, the higherthe degradation rates are. The degradation rate of AFB₁（20mg/L） turbid liquid afterirradiated twice at₁₀kGy is94.3%and₇4.9%, respectively. Compared to methanol waterdissolved AFB₁, the species of radiolytic products of AFB₁suspension was less, whichindicated that it might be water induced free radicals that caused the main reaction.Molecular structure information of four radiolytic products from water dissolved AFB₁wasobtained as well by the detection of LC-Q-TOF-MS. The molecular formulas of all theradiolysis products were C（17）H₁₄O₇, C₁₇H₁₂O₇, C₁₆H₁₂O₇and C₁₆H₁₀O₆, in which only C（17）H₁₄O₇has the same structure in methanol-water system（5） We studied the irradiation degradation mechanism of AFB₁in methanol-watersystem. The radiolysis procedure was regulated by setting different atmosphere andadditives including saturated N₂, saturated N₂O, saturated N2+isopropanol, saturatedN₂+H₂O₂and saturated N₂+tert-butyl alcohol. The radiation chemical yield G-values andthe irradiation degradation effects of each atmospheres were compared. The main freeradicals involved in the irradiation of AFB₁were determined. The contribution order offree radicals in radiolytic products of AFB₁was: HO₂，O₂->OH>eaq->H.（6） We studied the contamination of AFB₁in foodstuffs-peanut meal. Studies provedthat high levels of AFB₁in peanut meal were still able to degrade effectively. Thedegradation rate of sample （20mg/kg） after irradiation by20kGy was14.4%, and waterplayed a powerful role in radiation degradation process after the comparison with thedegradation rate of water, methanol-water and solid AFB₁. After the optimized extractionpurification steps in a very special way, the25radiolysis products was detected by usingLC-Q-TOF-MS in ion monitoring mode. Finally we foundtwo major products,319.0813m/z and331.0821m/z, which had same structure with those in methanol-water system.更多还原