Determination of optimal sample preparation for aldehyde extraction from pale malts and their quantification via headspace solid-phase microextraction followed by gas chromatography and mass spectrometry.

Aldehydes originating from malt play an important role in beer flavour deterioration. In order to better understand the influence of malting process on beer staling, it is necessary to acquire a reliable analytical methodology for determination of beer staling aldehydes in malt. Therefore, the aim of this study was to evaluate extraction parameters, which allow quantification of beer staling aldehydes present in pale malts. The method was validated with respect to linearity (R > 0.9988), limit of detection (0.28 - 0.99 µg/L), limit of quantification (0.92 - 3.31 µg/L), accuracy (± 5%), repeatability (1.3 - 5.3%) and intermediate precision (>20%). The following parameters of sample preparation were evaluated: sample amount, extraction time and temperature, ultrasonication time and oxygen level. Consequently, the best extraction conditions were successfully applied on pale malts. After extraction, the samples were analysed by headspace solid-phase microextraction (HS-SPME) with on fibre carbonyl derivatisation followed by gas chromatography and mass spectrometry (GC-MS). In addition, the salting-out effect during HS-SPME was studied. The method application allowed to identify significant differences (p ≤ 0.05) in the levels of aldehydes among various industrial scale, pale malts. The optimised method could give the information on the aldehyde content introduced into the brewing process and its potential contribution to the overall beer quality.

The interaction effect between vibrations and temperature simulating truck transport on the flavor stability of beer.

BACKGROUND: Beer flavor stability is important to brewers as a result of the increased global demand for beer. Increasing export leads to prolonged periods of transportation and storage and causes fresh flavor deterioration. Therefore, the present study examined the effect of different temperatures in combination with vibrations on beer quality. Beer was exposed to vibrations (50 Hz, 15 m s-2 , simulating transport) at 5, 30 and 45 °C for 22, 38 and 90 h and (for half the samples) aged for 60 days at 30 °C. RESULTS: The results obtained indicated decreased oxygen concentrations as a result of an elevated temperature and vibrations. There was no effect (P > 0.05) on color and a limited effect of temperature and vibrations on iso-α-acids. The parameters temperature and vibrations have a significant influence (P < 0.05) on aldehyde concentrations, namely total aldehydes, and especially '2-methylpropanal', '2-methylbutanal' and 'furfural'. CONCLUSION: The impact of vibrations on the aldehydes concentrations was substantial when subjected to an elevated temperature. Furthermore, a forced aging test of shorter duration than traditional methods might be developed. © 2018 Society of Chemical Industry.

Including experimental uncertainty on the independent variables when modelling microbial dynamics: The combined effect of pH and acetic acid on the growth rate of E. coli K12.

Modelling methods applied in predictive microbiology generally neglect the importance of uncertainty on the measurement of the independent variables. The Ordinary Least Squares (OLS) method that is commonly applied in predictive microbiology is only applicable if the experimental error on the inputs of the model are insignificant. However, this does not apply for many types of experimental measurements of the independent variables. Therefore, a parameter estimation method was adapted in this research for the estimation of the parameters of secondary models, taking into account uncertainty on the measurement of the influencing food characteristics. This parameter estimation method was based on the work of Stortelder (1996) and is referred to as the Weighted Total Least Squares method (WTLS). The method is formulised as an extension of the commonly used OLS method. Consequently the current WTLS method (i) is easily implemented using similar numerical methods, (ii) reduces to an OLS method when the measurement error on the model inputs is negligible and (iii) enables the evaluation of the accuracy of the model parameter estimates based on the same approximations.

Fermentation assays reveal differences in sugar and (off-) flavor metabolism across different Brettanomyces bruxellensis strains.

Brettanomyces (Dekkera) bruxellensis is an ascomycetous yeast of major importance in the food, beverage and biofuel industry. It has been isolated from various man-made ecological niches that are typically characterized by harsh environmental conditions such as wine, beer, soft drink, etc. Recent comparative genomics studies revealed an immense intraspecific diversity, but it is still unclear whether this genetic diversity also leads to systematic differences in fermentation performance and (off-)flavor production, and to what extent strains have evolved to match their ecological niche. Here, we present an evaluation of the fermentation properties of eight genetically diverse B. bruxellensis strains originating from beer, wine and soft drinks. We show that sugar consumption and aroma production during fermentation are determined by both the yeast strain and composition of the medium. Furthermore, our results indicate a strong niche adaptation of B. bruxellensis, most clearly for wine strains. For example, only strains originally isolated from wine were able to thrive well and produce the typical Brettanomyces-related phenolic off-flavors 4-ethylguaiacol and 4-ethylphenol when inoculated in red wine. Sulfite tolerance was found as a key factor explaining the observed differences in fermentation performance and off-flavor production. Sequence analysis of genes related to phenolic off-flavor production, however, revealed only marginal differences between the isolates tested, especially at the amino acid level. Altogether, our study provides novel insights in the Brettanomyces metabolism of flavor production, and is highly relevant for both the wine and beer industry.