Detection of volatile spoilage metabolites in fermented cucumbers using nontargeted, comprehensive 2-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS).

A nontargeted, comprehensive 2-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) method was developed for the analysis of fermented cucumber volatiles before and after anaerobic spoilage. Volatile compounds extracted by solid-phase microextraction were separated on a polyethylene glycol 1st-dimension column and 14% cyanopropylphenyl 2nd-dimension column. Among 314 components detected in fermented cucumber brine, 199 had peak areas with coefficients of variation below 30%. Peak identifications established by mass spectral library matching were 92% accurate based on 63 authentic standards. Analysis of variance of analytes' log peak areas revealed 33 metabolites changed in concentration after spoilage (P < 0.05), including increases in acetic, propanoic, and butyric acids, n-propyl acetate, several alcohols, and a decrease in furfural. GC×GC-TOFMS with a nontargeted, semi-automated approach to data analysis made possible the separation, identification, and determination of differences in polar volatile components, facilitating the discovery of several metabolites related to fermented cucumber spoilage. Practical Application: An optimized method for the chemical analysis of volatile food components is described and applied to the profiling of volatile compounds in fermented cucumbers, resulting in the identification of 137 components, many of which are being reported for the first time in fermented cucumbers. This nontargeted GC×GC-TOFMS method and inclusive data analysis platform facilitated the discovery of several metabolites that were formed or utilized during anaerobic spoilage of fermented cucumbers. Further study of these metabolites will enhance our ability to understand and potentially control the metabolism of spoilage bacteria that can degrade lactic acid under the restrictive environmental conditions present in fermented cucumbers.