Characterization of volatile metabolites formed by molds on barley by mass and ion mobility spectrometry

Abstract

The contamination of barley by molds on the field or in storage leads to the spoilage of grain and the production of mycotoxins, which causes major economic losses in malting facilities and breweries. Therefore, on-site detection of hidden fungus contaminations in grain storages based on the detection of volatile marker compounds is of high interest. In this work, the volatile metabolites of 10 different fungus species are identified by gas chromatography (GC) combined with two complementary mass spectrometric methods, namely, electron impact (EI) and chemical ionization at atmospheric pressure (APCI)-mass spectrometry (MS). The APCI source utilizes soft X-radiation, which enables the selective protonation of the volatile metabolites largely without side reactions. Nearly 80 volatile or semivolatile compounds from different substance classes, namely, alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, alkenes, terpenes, oxidized terpenes, sesquiterpenes, and oxidized sesquiterpenes, could be identified. The profiles of volatile and semivolatile metabolites of the different fungus species are characteristic of them and allow their safe differentiation. The application of the same GC parameters and APCI source allows a simple method transfer from MS to ion mobility spectrometry (IMS), which permits on-site analyses of grain stores. Characterization of IMS yields limits of detection very similar to those of APCI-MS. Accordingly, more than 90% of the volatile metabolites found by APCI-MS were also detected in IMS. In addition to different fungus genera, different species of one fungus genus could also be differentiated by GC-IMS.

Volatile Organic Compound Profile Fingerprints Using DART–MS Shows Species-Specific Patterns in Fusarium Mycotoxin Producing Fungi

“…APCI, HESI, PTR, SIFT, and other related techniques can be expected to have similar inherent VOC selectivities [9]. Previous studies utilizing such techniques have identified several VOCs from Fusarium isolates based upon comparison to public databases and published reports of microbial VOCs [12]. The distinctive ions observed here do not appear to overlap with previously published Fusarium VOCs.…”

“…In contrast to techniques dependent upon gas-phase proton-transfer reactions, GC-EI-MS based approaches will have different selectivities. Other researchers have explored the complementary potential in using both EI and proton transfer-based techniques [12].…”

“…Analytical techniques are available for both qualitative and quantitative analysis of VOCs [12,13]. Mass spectrometry (MS) has been utilized for the specific and sensitive analysis of VOCs [9].…”

Mass Spectrometry: A Rosetta Stone to Learn How Fungi Interact and Talk

“…Coating materials include divinylbenzene (DVB), polydimethylsiloxane (PDMS), carboxen (CAR), polyacrylate (PA) and carbon wide range (CWR). These coatings have been used solely or in combination (Table 1) [113,130,163]. Hence, SPME-based sampling consists of the preconcentration of the VOCs on a fiber via absorption, and the later thermal desorption (delivered) of the captured volatiles to the GC column or directly to the mass spectrometer instrument (see Figure 2) [114,128].…”

“…Other chromatographic techniques use two consecutive separation columns (2-dimensional liquid chromatography) or columns of different sorbent chemistry, such as ionic exchangers (see Table 1) [14,113,129,134,143]. The most common ionization techniques used in combination with 2D liquid chromatography are the ambient pressure ionization techniques, such as electrospray ionization (ESI) [134,135,137,138,[140][141][142][143][144][145]150] and atmospheric pressure chemical ionization (APCI) [139,146].…”