The gas accumulating in the head space of the serum bottleswas
measured and sampled initially after 12 h of contact time and every
24 h thereafter, up to 240 h. The gas production volume was
collected using syringes. Before each sampling, a 60-mL syringe
was used to equilibrate the pressure inside the bottle to the
ambient pressure, and the volume in the syringe was recorded as
the total gas volume. A Hamilton Syringe 1710N with a capacity of
100 mL was used to draw the gas from each serum bottle. This
volume was reduced to 50 mL by releasing the rest of the gas to
ensure that no liquid was drawn from the serum bottle. This
extracted gas was then injected into a gas chromatograph. The
components of the gas were analyzed using the gas chromatograph
(GC) (PerkinElmer, USA) equipped with a thermal conductivity
detector (TCD). The chromatographic operating conditions used for
the gas samples determination were adopted after Khanal et al.
(2004).