【作者】 王蓓；

【导师】 马海乐；

【作者基本信息】 江苏大学 ， 食品科学， 2014， 博士

【摘要】 霉菌和其代谢产生的毒素是导致粮食减产和影响人类健康的主要因素,稻谷作为我国最重要的粮食受到的黄曲霉菌和黄曲霉毒素侵害最为严重。因此,本文旨在保证稻谷品质的前提下,开发稻谷杀菌降毒素的新方法,以阻止霉菌污染产生毒素或直接降解毒素。研究了脉冲强光和紫外辐射技术的杀菌机理；通过反应动力学研究脉冲强光和紫外辐射技术的杀菌特征；对脉冲强光杀菌工艺进行了优化；研究新收获稻谷和储藏稻谷的红外热辐射杀菌工艺；评估脉冲强光降解不同介质中黄曲霉毒素的效果及降解动力学特征,测定降解产物的生物毒性和致突变毒性。通过对脉冲强光和紫外辐射对黄曲霉菌孢子的显微观察及现有理论归纳表明：脉冲强光辐射能够利用其高能光化和光热作用破坏孢子细胞壁结构导致细胞壁穿孔、皱缩,菌体胞浆物质外渗,阻碍其代谢而致死。紫外辐射对细胞壁无直观可见损伤,孢子的崩溃是由于紫外光直接对胞内物质干扰而进行的代谢阻碍。以辐射通量作为变量,对脉冲强光和紫外辐射杀菌效果进行研究,二者得到的孢子失活曲线分别对Weibull+Tail模型和Weibull模型拟合度高。比较两种辐射杀菌方法的单位能量消耗和杀菌速率得到：紫外杀菌能量利用率较高,而脉冲强光杀菌速率较快。紫外辐射处理可以在7min内杀死琼脂表面105cfu/g孢子,同样的效果脉冲强光只需要30s。脉冲强光结合保温处理的工艺可以极大提高杀菌效果并同时起到干燥稻谷的作用,杀菌数可达到5.2log cfu/g,干燥速率可达4.4%每分钟,干燥后稻谷水分可降低4.1个百分点。并且经各项指标测定,均未显示本研究方法对碾米质量有不良影响。对于新收获不同水分含量的稻谷和因不当的储藏条件等造成霉菌二次污染的稻谷,均可通过红外辐射快速加热稻谷至60℃然后在同样温度下保温不同时间来达到所需的杀菌干燥效果。对于新收获的初始水分含量高于21.1%的稻谷,推荐条件为红外辐射至60℃,保温120min,黄曲霉孢子可降低达8.3log cfu/go水分含量对杀菌效果起着至关重要的作用,水分含量越高,杀菌效果越好,因此将干燥的储藏稻谷表面润湿再进行热杀菌,可以显著提高杀菌效果。储藏稻谷杀菌的推荐条件为将谷壳润湿至稻谷整体水分含量为19.4%后进行红外热辐射处理至60℃,保温20min和自然冷却,黄曲霉孢子可降低7.2log cfu/g,最终水分含量为13.8%,可直接继续安全储藏而不需额外的干燥处理。脉冲强光对黄曲霉毒素Bi (AFB1)和黄曲霉毒素B2(AFB2)有极强的降解效果。HPLC检测定量分析显示,高浓度(500ppb)黄曲霉毒素B1和B2经过脉冲强光处理10s,在辐射通量为28.52J/cm2的条件下可分别降低96.6%和91.7%。降解动力学符合二级动力学方程,降解速率与黄曲霉毒素初始浓度和辐射强度成正比。卤虫无节幼体对黄曲霉毒素降解产物生物毒性检测以及彷徨试验对其致突变毒性检测显示,经脉冲强光处理后AFB1和AFB2降解产物的生物毒性和致突变毒性完全消除。脉冲强光对不同介质中黄曲霉毒素均具有很好的降解效果。处理稻谷时,在辐射通量为84.35J/cm2的条件下,AFB1和AFB2分别降低75.0%和39.2%。处理米糠时,在辐射通量为16.10J/cm2的条件下,AFB1和AFB2分别降低90.3%和86.7%。脉冲强光降解黄曲霉毒素符合二级动力学方程。研究表明,紫外、脉冲强光和红外热辐射对稻谷的黄曲霉菌杀灭效果理想。脉冲强光降解黄曲霉毒素效果理想。紫外、红外辐射技术尤其是高能脉冲强光辐射技术是一类可以应用于提高稻谷安全质量的高效、环保的杀菌脱毒技术。更多还原

【Abstract】 Fungi and their mycotoxins produced in grains are the main factors that cause the reduction of output and affection of human health. Rice as the most important food in China is facing the most serious problem on pollution of Aspergillus flavus and aflatoxins. Therefore, new methods of simultaneous decontamination and detoxication were developed. The mechanisms of inactivation of pulsed light (PL) and ultraviolet radiation technology were studied. The reaction kinetics characteristics of PL and ultraviolet radiation were investigated. The PL sterilization process was optimized. Infrared radiation disinfection process on freshly harvest rice and stored rice were studied. PL degradation effects of aflatoxin and degradation kinetics in different medium and biological toxicity and genetic toxicity of degradation products were determined.The study of the inactivation mechanism of PL and ultraviolet radiation on Aspergillus flavus spores showed that, PL radiation destroied spore cell wall structure and led to cell wall perforation and shrinkage by producing the high-energy photochemical and photothermal effects, which caused the the leakage of cytoplasm and cell death. Ultraviolet radiation has non-visible damage on the cell wall. The spore collapse was due to the ultraviolet radiation directly effect on the material intracellular.By setting the radiation fluence as a variable, the sterilization effect of pulsed light and ultraviolet radiation were studied. The inactivation curves well fitted the Weibull+Tail model and Weibull model. After comparing the unit energy consumption and inactivation rate, the obtained results showed that, ultraviolet has higher unit energy consumption and PL has higher inactivation rate. It needed7min for ultraviolet to inactive105cfu/g spores and for the same inactivation populations, PL only need30s.The combined PL and holding processing can greatly improve the inactivation effect and simutanious drying of rice. The reduction could achieved5.2log cfu/g, the drying rate could reached up to4.4%per minute. After drying, moisture can be reduced by4.1percentage points. And after checking the quality indexes, no negative effects were showed on rice milling quality.The freshly harvest rice with different initial moisture content (IMC) could be treated by infrared radiation heating to60℃and holding at same temperature for different time to achieve sterilization and drying effect. For the rice with IMC higher than21.1%, the optimal conditions was infrared radiation to60℃, holding for120min, Aspergillus flavus spores could reduce8.3log cfu/g. The MC plays a vital role in sterilization, the higher MC lead to higher sterilization effect. Therefore, wetting the surface of dried rice and followed by infrared heating, could significantly improve the disinfection effect. The optimal conditions for sterilization of stored rice was wetting husk to obtain the whole MC of19.4%and treated by infrared radiation at60℃and followed by20min of holding and natural cooling. Aspergillus flavus spores can be reduced by7.4log cfu/g and final moisture content of13.8%. The rice can be safe storage directly.PL has strong degradation effect on aflatoxin B1(AFB1) and aflatoxin B2(AFB2). HPLC analysis showed, after exposed for10s of PL, at fluence of28.52J/cm2, the aflatoxin B1and B2at high concentration (500ppb) could be reduced by96.6%and91.7%respectively. The degradation dynamics was well fitted the second order kinetic model. The biological toxicity and genotoxicity of the degradation products were measured by using Artemia nauplii and Ames test methods. The results showed the toxicities were completely eliminate after the PL treatment.PL has good degradation effects on different medium. For rough rice treated at the fluence of84.35J/cm2, AFB1and AFB2were decreased by75.0%and39.2%, respectively. For rice bran treated at the fluence of16.1J/cm, AFB1and AFB2were decreased by90.3%and86.7%, respectively. The PL degradation kinetics fitted the second order reaction. The degradation rate has positive relationship with the initial aflatoxin concentration and radiation intensity.Research showed that, ultraviolet, pulsed light and infrared radiation could greatly inactive on rice Aspergillus flavus. PL could reduce of aflatoxin toxin as well. Ultraviolet, infrared radiation technology and especially the high energy PL radiation technology are a group of light technologies which can be applied to improve the food safety, environmental friendly, energy efficiency technologies on rice.更多还原