Solid-phase extraction (SPE), solid-phase microextraction (SPME) using carbowax/divinylbenzen fiber, and stir bar sorptive extraction (SBSE) followed by solvent back extraction have been used for the extraction of free fatty acids (caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, stearic, oleic, linoleic, and linolenic acids) from beer. Subsequent gas chromatographic analyses with flame ionization detection were used for the determination of these compounds. Medium-chain fatty acids (caproic-lauric acid) were determined as free acids, and long-chain fatty acids (myristic-linolenic acids) were determined as methyl esters after methylation by BF(3)-methanol 14%. Linearity, recovery, and repeatability of all methods have been determined and compared with the SPE method used as a reference (SPME method was used only for medium-chain fatty acid determination). All three procedures provide similar working parameters characterized by high repeatability (2.3-16.3%) and good linearity (correlation coefficient ranging from 0.9919 to 0.9999). Results of beer analyses obtained by using these three methods were highly correlated. Although all methods provide compatible alternatives, for medium-chain fatty acid analysis SPME may be a more appropriate technique due to its operational simplicity, repeatability, and low cost.

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J. Inst. Brew. 113(2), [154][155][156][157][158] 2007 This work presents the development of a simple, rapid and low cost method for the determination of some beer flavours as esters such as isoamyl acetate, ethyl caproate, ethyl caprylate, phenyl acetate, ethyl caprate, phenylethyl acetate, ethyl laurate, ethyl myristate and ethyl palmitate using stir bar sorptive extraction (SBSE). The combination of this extraction technique with solvent back extraction and subsequent gas chromatographic analysis with flame ionisation detection was used for the determination of these compounds. The effects of different mixtures of organic solvents and the influence of sampling time and time of solvent back extraction were studied. An optimum procedure for the SBSE method was developed. The method had high repeatability (RSD 2.1-7.3%), good linearity (the correlation coefficients were higher than 0.9995 for quadratic fit over the concentration range from 0.015 to 30 mg/L) and acceptable recoveries (78-107%) and precision (RSD < 7.3%).

The rate of beer aging is affected by storage conditions including largely time and temperature. Although bottled beer is commonly stored for up to 1 year, sensorial damage of it is quite frequent. Therefore, a method for retrospective determination of temperature of stored beer was developed. The method is based on the determination of selected carbonyl compounds called as "aging indicators", which are formed during beer aging. The aging indicators were determined using GC-MS after precolumn derivatization with O-(2,3,4,5,6-pentaflourobenzyl)hydroxylamine hydrochloride, and their profile was correlated with the development of old flavor evolving under defined conditions (temperature, time) using both a mathematical and statistical apparatus. Three approaches, including calculation from regression graph, multiple linear regression, and neural networks, were employed. The ultimate uncertainty of the method ranged from 3.0 to 11.0 °C depending on the approach used. Furthermore, the assay was extended to include prediction of beer tendency to sensory aging from freshly bottled beer.

Esters represent one of the most important flavour groups in beer. The aim of this work was focused on the comparison of two optimized, simple, rapid and low cost methods, the solidphase microextraction technique and the stir bar sorptive extraction technique, for the determination of beer esters, in particular isoamyl acetate, ethyl caproate, ethyl caprylate, ethyl caprate, phenylethyl acetate, ethyl laurate, ethyl myristate, and ethyl palmitate. Subsequent gas chromatographic analyses with flame ionization detection were used for the determination of these compounds. Linearity, recovery, and repeatability of these methods were compared. Working parameters of both procedures were similar and characterized by high repeatability (2.1-7.3%) and good linearity (correlation coefficient ranging from 0.9991 to 0.9999). Results obtained by these two procedures were in good correlation.

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Sledování obsahu vicinálních diketonů-2,3-butandionu (diacetylu) a 2,3-pentandionu-v pivu je důležité, neboť při překročení prahové koncentrace vnímání dochází k nepříjemnému ovlivnění senzorických vlastností piva označovanému jako máselné aroma. Práce se zabývá vývojem a optimalizací metody sorpční extrakce na míchací tyčince (SBSE), moderního postupu používaného při přípravě vzorků, pro stanovení vicinálních diketonů v pivu. Pracovní charakteristiky této metody byly porovnány s parametry mikroextrakce na pevné fázi (SPME). Vlastní selektivní stanovení diacetylu a pentandionu bylo provedeno na plynovém chromatografu vybaveném detektorem elektronového záchytu.