Beer volatile analysis: optimization of HS/SPME coupled to GC/MS/FID.

Journal of food science (2011-05-04)
Gustavo Charry-Parra, Maritza Dejesus-Echevarria, Fernando J Perez
ABSTRACT

A powerful technique was developed for the identification and quantification of 9 volatile compounds of beer, using headspace solid phase micro-extraction (HS/SPME) and gas chromatograph coupled to a mass spectrometer and a flame ionization detector (GC/MS/FID). Optimized parameters included type of fiber, desorption time, and exposure time. Optimization was achieved with standard solutions of the target compounds. All samples were analyzed in triplicate. An exposure time of 45 min with PDMS fiber in the sample headspace was enough to reach equilibrium of the phases. A desorption time of 15 min in the gas chromatograph injector was enough for the fiber to desorb the target compounds. It was found that less polar compounds were more readily absorbed by the fiber (for example, isoamyl acetate) than more polar compounds (for example, acetaldehyde), under the extraction conditions, due to the nature of the fiber. Extraction conditions are important criteria to perform a good quantification of volatile compounds. Concentrations found in sampled beer, for the compounds of interest, ranged between 0.32 and 41.7 ppm. Results show that the reproducibility of the technique depends on the compounds. Esters have higher values (RSD mean value 5.05%) than higher alcohols (RSD mean value 2.5%) and aldehydes (RSD 3.7%). The simplicity of the validated methodology enables its use as a regular quality control procedure for beer flavor analysis. This study describes a technique successfully used to identify and quantify volatiles of interest in beer that can be used for quality control purposes under normal brewery production conditions. The technique uses a gas chromatograph coupled to a mass spectrometer with a flame ionization detector.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Isoamyl acetate, ≥95%, FCC, FG
Sigma-Aldrich
Isopentyl acetate, anhydrous, ≥99%
Sigma-Aldrich
Isoamyl acetate, natural, ≥97%, FCC, FG
Supelco
Isopentyl acetate, analytical standard
Sigma-Aldrich
Isopentyl acetate, mixture of isomers, reagent grade, 98%
Supelco
SPME Portable Field Sampler, coating PDMS
Supelco
SPME/HPLC Interface, rheodyne valve version
Supelco
SPME Sampling Stand, for use with 15 mL vials
Supelco
SPME Portable Field Sampler, coating CAR/PDMS
Supelco
SPME Sampling Stand, for use with 4 mL vials
Supelco
SPME Portable Field Sampler, coating PDMS/DVB
Supelco
SPME fiber assortment kit 3
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 75 μm (CAR/PDMS), for use with manual holder, needle size 24 ga
Supelco
SPME fiber assembly Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS), needle size 24 ga, for use with manual holder
Supelco
SPME fiber assembly polyacrylate (PA), df 85 μm (PA), for use with manual holder, needle size 24 ga
Supelco
SPME fiber assembly Polydimethylsiloxane (PDMS), df 7 μm (PDMS), needle size 24 ga, for use with manual holder
Supelco
SPME Fiber Assembly Polydimethylsiloxane/Divinylbenzene (PDMS/DVB), df 60 μm (PDMS/DVB), for use with autosampler/HPLC, needle size 24 ga, StableFlex fiber
Supelco
SPME fiber assembly, Carbowax-Polyethylene Glycol (PEG) Coating, needle size 23 ga, df 60 μm (PEG), metal alloy fiber, for use with manual holder
Supelco
SPME fiber assortment kit 1, for use with manual holder, needle size 24 ga
Supelco
SPME fiber assortment kit 2, for use with manual holder, needle size 24 ga
Supelco
SPME fiber assortment kit 4, for use with manual holder, size 24 ga
Supelco
SPME fiber assortment kit 5, needle size 23 ga, for use with autosampler
Supelco
SPME LC Tips, C18, tray of 96 ea
Supelco
SPME StableFlex fiber assortment kit, for use with manual holder
Supelco
SPME-OC Fiber Assembly, Polydimethylsiloxane/Divinylbenzene (PDMS/DVB), df 75 μm (Coating thickness includes 65 μm coating + 10 μm OC (overcoating)), needle size 23 ga, pkg of 3 ea, fiber L 1 cm
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 75 μm (CAR/PDMS), needle size 23 ga, for use with manual holder
Supelco
SPME fiber assembly Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS), needle size 24 ga, StableFlex, for use with manual holder/autosampler
Supelco
SPME fiber assembly polyacrylate (PA), df 85 μm (PA), for use with autosampler, needle size 24 ga
Supelco
SPME fiber assembly Polydimethylsiloxane (PDMS), df 7 μm (PDMS), needle size 24 ga, for use with autosampler
Supelco
SPME Fiber Assembly Polydimethylsiloxane/Divinylbenzene (PDMS/DVB), df 65 μm (PDMS/DVB), needle size 24 ga, for use with manual holder