Abstract
A fully automatic membrane inlet mass spectrometric (MIMS) on-line
instrumentation for the analysis of aroma compounds in continuous beer
fermentation processes was constructed and tested. The instrumentation
includes automatic filtration of the sample stream, flushing of all
tubing between samples and pH control. The calibration standards can be
measured periodically. The instrumentation has also an extra sample line
that can be used for off-line sample collection or it can be connected
to another on-line method. Detection limits for ethanol, acetic acid and
eight organic beer aroma compounds were from μg l−1 to low mg l−1
levels and the standard deviations were less than 3.4%. The method has a
good repeatability and linearity in the measurement range. Response
times are shorter than or equal to 3 min for all compounds except for ethyl caproate, which has a response time of 8 min.
In beer aroma compound analysis a good agreement between MIMS and
static headspace gas chromatographic (HSGC) measurements was found. The
effects of different matrix compounds commonly present in the
fermentation media on the MIMS response to acetaldehyde, ethyl acetate
and ethanol were studied. Addition of yeast did not have any effect on
the MIMS response of ethanol or ethyl acetate. Sugars, glucose and
xylose, increased the MIMS response of all studied analytes only
slightly, whereas salts, ammonium chloride, ammonium nitrate and sodium
chloride, increased the MIMS response of all three studied compounds
prominently. The system was used for on-line monitoring of continuous
beer fermentation with immobilised yeast. The results show that with
MIMS it is possible to monitor the changes in the continuous process as
well as delays in the two-phase process.
Original language | English |
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Pages (from-to) | 1254-1263 |
Journal | Talanta |
Volume | 65 |
Issue number | 5 |
DOIs | |
Publication status | Published - 2005 |
MoE publication type | A1 Journal article-refereed |
Keywords
- on-line measurement
- on-line analysis
- membrane inlet mass spectrometry
- continuous beer fermentation
- matrix effects