present in low concentrations. Thus, for accurate interpretation, it is crucial to
obtain as many volatile components as possible from the samples, therefore, the
desired sampling technique must be able to extract different polar and structural
biological VOCs.
Over time, many strategies have been applied in thefield of MVOC detection
and concentration. Steam distillation (Vanhaelen et al. 1978 ; Kaminski et al. 1972 ),
liquid–liquid extraction (Wu et al. 2005 ), and simultaneous distillation extraction
are some of the conventional methods that were employed by the researchers. They
required long extraction times, large amounts of solvents, and multiple steps. These
methods also result in degradation of unstable volatiles such as alkene, ester, and
some unsaturated VOCs. However, because of their simplicity, they are still
extensively applied for the fragrance-and-aroma characterization. Another method
for collection of microbial volatiles is purging and trapping. In studies of odor
formation in moist cereal grain during granary storage, the volatiles were collected
by the withdrawal of intergranular air through adsorbent cartridges (Abramson et al.
1980 , 1983 ). Norrman ( 1977 ) developed a fast method to study volatile production
by direct injection of a headspace sample into a gas chromatograph with a packed
column.
However, currently the widely used method is headspace solid-phase microex-
traction method (HS-SPME) because it integrates the extraction, concentration, and
introduction in one step thus resulting in reduced preparation time and simultaneously
increasing sensitivity over other extractions (Tait et al. 2014 ). The HS-SPME pro-
cedure includes introduction of fused silicafiber coated with a polymeric organic
material into the headspace above the sample. The volatile organic analytes are
extracted and concentrated in thefiber coating and then transferred to the analytical
instrument which is mostly gas chromatograph for thermal desorption and analysis.
The technique has great importance in microbiological studies and food technology
(Zhang and Pawliszyn 1993 ; Nilsson et al. 1995 ). Thefiber chosen for extraction may
have a marked effect on the detected VOC profile. Differentfiber coatings are com-
mercially available for SPME, like polydimethylsiloxane, carbowax-divinylbenzene
(Jia et al. 2010 ), and polyacrylate (Buchholz et al. 1994 ) that have exclusively been
applied to the analysis of phenols. Only for a few phenols comparative results are
available, indicating higher sensitivity with the polyacrylate than with the poly-
dimethylsiloxanefiber coating for these more polar compounds.
After extraction, analysis of samples is performed by coupled (GC) and mass
spectrometry (MS) (Madrera et al. 2005 ). Other methods of volatile analysis include
comprehensive two-dimensional gas chromatography (Welke et al. 2014 ), ion trap
mass spectrometry (Noguerol et al. 2009 ), or time-of-flight mass spectrometry
(Bordigaetal. 2014 ).Amonginnovativeprocedures, near-infrared (NIR)spectroscopy
is becoming popular in thefield of volatile studies as a rapid, accurate, simple to
operate, as it requires no sample pretreatments prior to analysis (Buratti et al. 2011 ).
Recently, Ye et al. ( 2016 ) have used this method in detecting volatiles in apple wines.
Near-infrared region of the electromagnetic spectrum (700–2500 nm) provides more
sophisticated structural information based on the variation behaviors of combinations
of bonds (Bauer et al. 2008 ; Reid et al. 2006 ). Proton transfer reaction-mass
242 D. Chandra et al.