Detection of Volatile Spoilage Metabolites in Fermented Cucumbers Using Nontargeted, Comprehensive 2‐Dimensional Gas Chromatography‐Time‐of‐Flight Mass Spectrometry (GC×GC‐TOFMS)

Abstract

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.

Characteristics of Spoilage-Associated Secondary Cucumber Fermentation

“…Acetic acid is one of the end products of that metabolism (37), which is consistent with the increased concentrations of acetic acid in the spoiled commercial fermentations presenting high counts of MB1 colonies. Although 1,2-propanediol has been identified as a metabolic product of lactic acid degradation by L. buchneri (37), previous characterization of the metabolites in spoiled fermented cucumber samples did not detect this alcohol (23)(24)(25). This alcohol can subsequently be converted into propionic acid by other microorganisms belonging to the lactobacillus family.…”

Metabolomic Technologies for Improving the Quality of Food: Practice and Promise

“…Furthermore, Koek et al (2008) found that a polar/nonpolar column combination resulted in better resolution of components and greater use of the separation space with similar separation efficiency. This technology has been successfully adapted for the nontargeted profiling of volatile compounds in fermented cucumber ( Johanningsmeier & McFeeters 2011) and metabolic footprinting of Lactobacillus buchneri during fermented cucumber spoilage ( Johanningsmeier & McFeeters 2015), resulting in the identification of 92 volatile and nonvolatile compounds related to spoilage from several thousand metabolite peaks detected.…”

Pellicle formation, microbial succession and lactic acid utilisation during the aerobic deteriorating process of Sichuan pickle

“…Productions of unpleasant odour and plant cell wall degrading enzymes (PCWDEs) are the well-characterised biochemical activities of vegetable spoilage organisms (Johanningsmeier & McFeeters, 2011;Lee et al, 2013). But the growth of these undesirable organisms is always inhibited by the acid stress thanks to the low-pH environment of pickle product (Fleming et al, 1983).…”