Automated Dual-Chamber Sampling System to Follow Dynamics of Volatile Organic Compounds Emitted by Biological Specimens

Growth
of microorganisms is often accompanied by the release of
volatile organic compounds (VOCs). The released VOCs may qualitatively
or quantitatively reflect the physiological states of microbial cultures.
A number of VOCs are produced during microbial degradation of organic
matter accompanying food spoilage. In order to characterize the dynamics
of microbial VOC production, and enable time-dependent analysis, we
have constructed a dual-chamber sampling system and coupled it online
with mass spectrometry (MS). The biological specimen is placed in
a gas-tight sampling chamber. A carrier gas is introduced to the chamber
periodically to transfer the VOCs present in the specimen headspace
to the atmospheric-pressure chemical-ionization interface of a triple-quadrupole
mass spectrometer. A control or blank spectrum is recorded before
the specimen spectrum is recorded at each time point, enabling signal
comparison and subtraction. The custom-made electronic control unit,
incorporating three Arduino microcontrollers, operates six pinch valves
and a miniature air compressor and triggers MS-data acquisition. The
automated dual-chamber sampling system was first tested using standard
mixtures to verify its analytical performance. To demonstrate the
usefulness of this system in the studies of microbial volatomes, we
implemented it in real-time monitoring of the growth of baker’s
yeast (Saccharomyces cerevisiae), fructification
of golden oyster mushroom (Pleurotus citrinopileatus), and microbial degradation of a food-related sample (Pacific white
shrimp, Litopenaeus vannamei). The recorded VOC signals
show characteristic temporal profiles with transient bands or plateaus
corresponding to different stages of microbial growth and putrefaction
processes.