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《现代养猪生产技术》读者互动专区

《现代养猪生产技术》读者互动专区

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详解隐性霉菌毒素的检测方法(二)

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kk 发表于 2016-8-17 12:33:19 | 显示全部楼层 |阅读模式

在过去的5至6年前,当霉菌毒素研究者初步发现植物具备合成毒素共轭化合物的能力时,低估了这种新化合物带来的危害。毒素出现的这种化学、生理特性的改变,及相应的检测和鉴定方法的改变,研究者将这种代谢反应产物称之这“隐性霉菌毒素”。加拿大圭尔夫大学的动物和家禽科学系的 Trevor Smith博士指出,商业ELISA检测法将只能检测出游离状态的DON,而共轭毒素则检测不出。这样便会出现大量的检测结果为阴性,但动物却表现出霉菌毒素中毒症状。
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当这种饲料饲喂给动物时,动物的消化过程可以水解这些霉菌毒素共轭化合物,释放出原始的毒素。虽然对这一机制还没有完全理解,但毒素的这种共轭现象将会导致对饲料中真实霉素水平的低估,低估水平最高可达88%,一旦在农场出现这种情况将很难找出源头。

虽然在过去几年里,学术界对隐性霉菌毒素的关注得到重视,但还需要更多的实地研究。希望这些工作可以帮助人们作出更加明智的决策。如果大家都没有看到霉菌毒素,便很难说明他们去寻找解决方案。

寻找全面解决方案

尽管目前检测和分析方法有所进步,但我们所知的真菌代谢物的化学多样性,仍然是制定全面检测方法的难题。已有500多种毒素得到鉴定,但这种传统分析方法仅得出少数毒素的化学结构图,少于10种。

随着霉菌毒素问题日趋复杂,故实地霉菌毒素的检测和控制程序也变得更加重要。既然霉菌毒素是个不可避免的问题,那么基于地区和饲料类型的全年检测策略,可以帮助预防大规模疾病的暴发。

鉴于霉菌毒素造成的重大经济、健康负面影响,故需增加对有害毒素的鉴定及更好的检测方法的研究。随着技术的发展,新的分析方法可以检测出样品中更全面的毒素水平。

展望未来

近期,研究者将HPLC和串联质谱技术配套用于鉴定饲料或食品样品中霉菌毒素和隐性霉菌毒素的结构,这种方法可同时检测多种毒素水平,一次最多可检测出同一个样品中87种霉菌毒素,检测更快速、更可靠、定量更准、效率更高。

其它新方法都集中于将基因组学和转录组学用于霉菌毒素直接分析。具体是使用活细胞与某些化合物反应,根据它们的类型,在基因表达中释放特殊的指纹。这些方法可识别毒素DNA的微折叠结构,用于评估特殊活细胞在从饲料或食品中分离出的霉菌毒素环境中,基因表达的特性。

对于如何降低饲料霉菌毒素的污染率时,在理解这些问题后首先需制定有效的治理对策。 Smith博士还指出,在对所有霉菌毒素结构鉴定完成之前,改进检测方法是至关重要的,因为目前的解决方案并不能全面解决这一难题。

附原文:
Testing for hidden mycotoxins

Masked mycotoxins?

In the last five to six years, a new and underestimated challenge presented itself when mycotoxin researchers discovered that plants have the ability to conjugate toxins. This suspected metabolic reaction to the presence of contaminants changes the chemical and physical characteristics of the toxin, and consequently, their detection or characterization, hence the term “masked mycotoxin.”

Dr. Trevor Smith, a professor in the department of Animal and Poultry Science at the University of Guelph  , Canada, said commercial ELISA tests will only pick up the free DON levels and the conjugated toxins will stay hidden, which causes animals to respond with mycotoxin symptoms even though test results don't show it.

When fed to animals, the digestive process is capable of hydrolyzing such conjugates and releasing the bioactive original mycotoxin molecule. Though not fully understood, the conjugation mechanism can lead to an underestimation of the real level of mycotoxin present in a feed material—even up to 88 percent—which can make it difficult to pinpoint the cause of issues on-farm.

“Although masked mycotoxins are getting attention in the last few years academically, more education is needed in the field. Hopefully such efforts will allow people to make more informed decisions,” Smith said. “If people can't see the mycotoxins, it's hard to convince them to find solutions.”

Finding a total solution?

While testing and analysis methods are improving, the chemical diversity of the currently known fungal metabolites presents a significant challenge in determining a complete solution for testing. More than 500 toxins have been identified, but traditional methodology may only give part of the picture of contamination, accounting for the presence of less than 10 of those.

As it becomes increasingly apparent just how complex the mycotoxin issue is, it is now more important than ever to have a mycotoxin testing and control program in place. While mycotoxins present an unavoidable issue, strategic testing throughout the year based on geographic location and feed type can assist in preventing major illnesses.

With the significant economic implications and negative health effects, increasing research is being dedicated to identifying harmful mycotoxins and creating better tests to screen for them. As technology improves, new analytical methodologies can present a more complete picture of the situation.

Looking ahead?

Recently, a strong emphasis has been seen in the use of HPLC coupled to tandem mass spectrometry techniques in the direct determination of profiles of mycotoxin and masked mycotoxins present in feed or food matrices in more rapid, reliable, quantifiable and efficient ways, thanks to multi-mycotoxin detection capabilities within a sample—with up to 87 mycotoxins analyzed at the same time on a given sample.

Other emerging approaches are focusing on the use of genomics and transcriptomics as tools for indirect mycotoxin analysis. These technologies use the ability of living cells to respond to the presence of chemicals by leaving specific fingerprints in the form of gene expression, according to their type. They could turn into new screening tools with the development of DNA microchips that will evaluate the gene expression profile of specific cells when in the presence of mycotoxins extracted from feed or food material.

When it comes to reducing the risks of contaminated feed, effective remediation strategies start with understanding the problem. And as Smith explains, “Improved testing is critical, because until we can see a clear picture of the challenges, solutions cannot adequately address the issues.”
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