Detection of volatile indicator compounds for biological contamination and deterioration of food

当水果因损坏、虫害或真菌和细菌感染而变质时，它会产生健康水果不会产生的特有气味化学物质。如果在恶化的早期阶段，在任何明显的迹象之前就能检测到这些化学物质，就可以节省种植者、分销商和零售商的大量浪费。虽然存在检测空气中微量化学物质的手段，但没有现有的方法来确定哪些化学物质具体与恶化的早期阶段有关。它们可能以极少量的形式存在，作为复杂的化学混合物的一部分，其中许多将以相对大量的形式存在。该项目将提供一种利用昆虫嗅觉的敏感度和辨别力来识别这些化学物质的方法，以便它们的检测可以用于监测水果的早期变质。这些方法也将适用于许多其他食物和情况。地中海果蝇在健康的水果中产卵，在这个项目中是橙子，幼虫随后会在那里发育，一段时间内看不到它们存在的外部迹象。我们知道蜜蜂可以对水果和感染相关的化学物质做出反应，它们将被训练来识别与这种侵扰有关的特定化学物质。这将通过给予蜜蜂糖奖励来实现，蜜蜂通过伸展鼻子或舌头来回应，同时让它们暴露在含有昆虫幼虫的水果的气味中，而当它们暴露在健康水果或受损但未被感染的水果的气味中时，没有任何奖励。训练结束后，即使没有奖励，它们也会伸展鼻子，对被污染的橙子的气味做出反应。来自虫害橙子的气味也将通过吸附到多孔聚合物上并用溶剂洗脱来收集，以提供所涉及的化学物质的溶液。这将包含许多额外的化学物质，但这些化学物质将通过气相色谱分离成单独的成分化学物质，然后依次吹过训练过的蜜蜂的触角，但一次一个。当蜜蜂接触到一种特殊的化学物质(S)，它用这种化学物质来区分受感染的水果和健康的水果，它会伸展鼻子，这种反应很容易观察和记录。然后，这些特殊的化学物质将通过标准分析方法进行鉴定，包括质谱学和核磁共振光谱学。作为对这些方法的检查，这些化学物质的样本将被获取并用于训练更多的蜜蜂，然后将这些蜜蜂暴露在被感染和未被感染的水果中，以确认它们是正确的化学物质。然后，便携式质谱仪将被编程，在实验室和加工和分销中心从水果的气味中寻找这些化学物质。

When fruit deteriorates because of damage, insect infestation or fungal and bacterial infections, it produces characteristic odour chemicals that are not produced by healthy fruit. If those chemicals were detectable at an early stage of deterioration, before there were any visible signs, it would save a lot of wastage by growers, distributors and retailers. Although the means of detecting traces of chemicals in the air exist there is no existing method for identifying which chemicals are specifically associated with the early stages of deterioration. They are likely to be present in tiny amounts as part of a complex mixture of chemicals, many of which will be present in relatively large quantities. This project will provide a means of identifying those chemicals, using the sensitivity and discriminatory power of insect olfaction, so that their detection can be used to monitor for the early deterioration of fruit. The methods will also be applicable to many other foods and situations. The Mediterranean fruit fly lays its eggs inside healthy fruit, oranges in this project, where the larvae will subsequently develop with no visible external signs of their presence for some time. Honeybees, that we know can respond to fruit and infection related chemicals, will be trained to recognise the specific chemicals associated with such an infestation. This will be done by giving the bees a sugar reward, to which they respond by extending their proboscis or tongue, at the same time as exposing them to the odours from fruit containing the insect larvae and no reward when exposed to the odours of healthy fruit or damaged but uninfested fruit. After training they will extend their proboscis in response to the odour from the contaminated orange even without a reward. The odours from insect-infested oranges will also be collected by adsorption onto a porous polymer and elution with a solvent to provide a solution of the chemicals involved. This will contain many additional chemicals but these will be separated by gas chromatography into the separate component chemicals which will be blown, sequentially but one at a time, across the antennae of a trained honeybee. When the bee is exposed to the particular chemical(s) that it uses to discriminate between infested and healthy fruit it will extend its proboscis, a response that is very easy to observe and record. These particular chemicals will then be identified by standard analytical methods including mass spectrometry and nuclear magnetic resonance spectroscopy. As a check on the methods, samples of the chemicals will be obtained and used to train more honeybees which will then be exposed to infested and uninfested fruit to confirm that they are the correct chemicals. Portable mass spectrometers will then be programmed to look for these chemicals in the odours from fruit, both in the laboratory and in the processing and distribution centres.