Evaluation of Solid-Phase Microextraction for the Isotopic Analysis of Volatile Compounds Produced during Fermentation by Lactic Acid Bacteria

Abstract

The use of solid-phase microextraction (SPME) coupled with isotope ratio mass spectrometry (IRMS) for the analysis of flavor compounds produced by lactic acid bacteria has been evaluated using both liquid and headspace sampling modes. Initially, it was necessary to optimize the conditions for the SPME extraction of flavors-diacetyl and acetoin-in standard aqueous solutions. The effects of salt, headspace versus liquid sampling, and coating phase were tested. Second, the suitability of the coupling of SPME and gas chromatography-combustion interface-IRMS (GC-C-IRMS) for the determination of delta(13)C values was assessed. It is shown that neither the analyte concentration nor the period of fiber exposure has an effect on the delta(13)C values. Finally, having verified that there are no matrix effects from the fermentation medium, it is reported for the first time that flavor compounds can be extracted directly from culture supernatant by SPME and their delta(13)C values can be obtained by GC-C-IRMS.

Metabolic flux in glucose/citrate co-fermentation by lactic acid bacteria as measured by isotopic ratio analysis

“…The SPME technique used to recover diacetyl and acetoin from the fermentation broth introduces a small consistent negative shift in the N 13 C values relative to those determined by EA-IRMS on encapsulated samples [9]. This shift is independent of the concentration present, allowing direct correction factors to be applied for diacetyl and acetoin.…”

“…The ¢ber was inserted into the headspace and retained for 10 min. Then, the ¢ber was retracted and directly transferred to the injection port of a GC linked via a combustion interface to an IRMS, as described previously [9].…”

Head Space Solid Phase Micro-Extraction (HS - SPME) of volatile organic compounds produced by Sporidiobolus salmonicolor (CBS 2636)

“…Studies about volatile organic compounds produced by Lactobacillus (GOUPRY et al, 2000), Trichoderma harzianum (FIEDLER; SCHUTZ; GEH, 2001), many species of Aspergillus and Penicillium (FIEDLER; SCHUTZ; GEH, 2001) and Staphylococci (VERGNAIS et al, 1998) are reported. The variability of yeast strains in their ability to produce volatile compounds has also been studied using SPME (MAURIELLO et al, 2009).…”

Dynamic Chemical Communication between Plants and Bacteria through Airborne Signals: Induced Resistance by Bacterial Volatiles

“…Their origins can be unambiguously determined by feeding precursor isotopes to PGPR cultures and monitoring for label enrichment in the released volatiles. Volatile compounds can be extracted directly from bacterial culture supernatants, and their 13 C enrichment levels can be obtained by GC coupled with isotope ratio mass spectrometry (IRMS) (Goupry et al 2000). …”