As a reference method an SPE method described by
Hage (17) was utilized with some changes. SPE columns Strata C18-E
200 mg/3 mL were purchased from Phenomenex (Torrance, CA). SPE
columns were activated with 2.5mL ofmethanol and washed by 5.0mL of
water. Then 20 mL of degassed beer sample with 1.0 mL of 1MHCl and
spiked with heptanoic and pentanedecanoic acids (each internal standard
at a concentration of 1.3 mg/L) was applied. A volume of 5.0 mL of water
was used for cleanup. The next step included drying under a mild nitrogen
flush. Chloroform (2 0.5 mL) was used for fatty acid elution. For the
determination of medium-chain fatty acids (C6-C12) 2 μL of this chloroform
extract was injected to the GC column. For the determination of
long-chain fatty acids (C14-C18) the chloroform extract was evaporated