Erler A, Riebe D, Beitz T, Löhmannsröben H-G, Grothusheitkamp D, Kunz T, Methner F-J
Physical Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam, 14476, Germany.
Department of Food Technology and Food Chemistry, Technische Universität Berlin, Seestr. 13, Berlin, 13353, Germany.
J Mass Spectrom. 2018 Oct;53(10):911-920. doi: 10.1002/jms.4210. Epub 2018 Aug 15.
Mold fungi on malting barley grains cause major economic loss in malting and brewery facilities. Possible proxies for their detection are volatile and semivolatile metabolites. Among those substances, characteristic marker compounds have to be identified for a confident detection of mold fungi in varying surroundings. The analytical determination is usually performed through passive sampling with solid phase microextraction, gas chromatographic separation, and detection by electron ionization mass spectrometry (EI-MS), which often does not allow a confident determination due to the absence of molecular ions. An alternative is GC-APCI-MS, generally, allowing the determination of protonated molecular ions. Commercial atmospheric pressure chemical ionization (APCI) sources are based on corona discharges, which are often unspecific due to the occurrence of several side reactions and produce complex product ion spectra. To overcome this issue, an APCI source based on soft X-radiation is used here. This source facilitates a more specific ionization by proton transfer reactions only. In the first part, the APCI source is characterized with representative volatile fungus metabolites. Depending on the proton affinity of the metabolites, the limits of detection are up to 2 orders of magnitude below those of EI-MS. In the second part, the volatile metabolites of the mold fungus species Aspergillus, Alternaria, Fusarium, and Penicillium are investigated. In total, 86 compounds were found with GC-EI/APCI-MS. The metabolites identified belong to the substance classes of alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, terpenes, and sesquiterpenes. In addition to substances unspecific for the individual fungus species, characteristic patterns of metabolites, allowing their confident discrimination, were found for each of the 4 fungus species. Sixty-seven of the 86 metabolites are detected by X-ray-based APCI-MS alone. The discrimination of the fungus species based on these metabolites alone was possible. Therefore, APCI-MS in combination with collision induced dissociation alone could be used as a supervision method for the detection of mold fungi.
发芽大麦籽粒上的霉菌会给麦芽制造和啤酒厂设施造成重大经济损失。其检测的可能替代物是挥发性和半挥发性代谢物。在这些物质中，必须识别出特征性标记化合物，以便在不同环境中可靠地检测霉菌。分析测定通常通过固相微萃取进行被动采样、气相色谱分离以及电子电离质谱（EI-MS）检测来完成，由于缺少分子离子，这种方法往往无法进行可靠的测定。另一种方法是GC-APCI-MS，一般来说，它可以测定质子化分子离子。商业大气压化学电离（APCI）源基于电晕放电，由于会发生多种副反应，通常具有非特异性，并且会产生复杂的产物离子光谱。为克服这一问题，本文使用了基于软X射线的APCI源。该源仅通过质子转移反应促进更具特异性的电离。在第一部分中，用代表性的挥发性真菌代谢物对APCI源进行了表征。根据代谢物的质子亲和力，检测限比EI-MS低多达2个数量级。在第二部分中，对曲霉属、链格孢属、镰刀菌属和青霉属霉菌的挥发性代谢物进行了研究。通过GC-EI/APCI-MS总共发现了86种化合物。鉴定出的代谢物属于醇类、醛类、酮类、羧酸类、酯类、取代芳香化合物、萜类和倍半萜类物质类别。除了对单个真菌物种非特异性的物质外，还发现了这4种真菌各自的特征性代谢物模式，从而能够可靠地区分它们。86种代谢物中有67种仅通过基于X射线的APCI-MS检测到。仅基于这些代谢物就可以区分真菌物种。因此，APCI-MS与单独的碰撞诱导解离相结合可作为检测霉菌的一种监测方法。
