JESSIKA DE CLIPPELEER (1), Filip Van Opstaele (1), Joeri Vercammen (2), Luc De Cooman (1), Guido Aerts (1)
(1) KaHo St.-Lieven, KULeuven Association, Laboratory of Enzyme,
Fermentation, and Brewing Technology, Gent, Belgium; (2) Interscience
BVBA, Interscience Expert Center, Louvain-la-Neuve, Belgium
Flavor stability remains one of the main quality criteria for beer,
and the urgency to control it is endorsed by the global beer market and
its allied need for longer storage times for exported beer. Formation
and release of volatile aldehydes is recognized as one of the main
causes of beer flavor deterioration upon storage. Most of these
compounds pre-exist abundantly in malt, and may vary significantly
between different malt types. As such, the staling potential of finished
beer is largely determined by the type of malt used in the brewing
process. Consequently, knowledge of malt aldehyde content is
indispensable for brewers in view of quality control, selection of the
appropriate malt variety, and objective assessment of the flavor
stability of processed beer. The potential of selected ion flow tube
mass spectrometry (SIFT-MS) to differentiate malted barley cultivars on
the basis of their headspace profiles has been investigated in this
study. Prime focus is on the analysis of aldehydes and particularly as
compared to the headspace solid-phase microextraction (SPME) gas
chromatography-MS method currently used. The investigated aldehyde
markers can be classified into Strecker degradation aldehydes
(2-methylpropanal, 2- and 3-methylbutanal, methional, benzaldehyde, and
phenylacetaldehyde), aldehydes formed during Maillard reactions
(furfural). and lipid oxidation aldehydes (hexanal and trans-2-nonenal).
SIFT-MS is an analytical technique that is based upon soft chemical
ionization taking place in a flow tube reactor. A commercial SIFT-MS
instrument (Voice200, Syft Technologies, Christchurch, New Zealand) was
equipped with a direct inlet and a heated external interface, which
provided direct entry of volatiles into the flow tube. Volatile
emissions from ungrounded malt grains were sampled with a
micro-chamber/thermal extractor (µ-CTE; Markes International,
Llantrisant, UK). Dynamic headspace with the µ-CTE uses a substantially
higher amount of material (25 g). As a result, higher absolute responses
are easily obtained without the need to increase extraction temperature
and without inducing stress-related emissions. By dynamic headspace
SIFT-MS, the target volatiles were readily identified in the different
malt headspaces. The technique exhibited an increase in specificity and
speed compared with the headspace SPME GC-MS procedure. The unique
feature of SIFT-MS to analyze malt sample headspaces rapidly and
directly without the need for sample preparation, derivatization, or
chromatographic preseparation is demonstrated. Principal component
analysis (PCA) was successfully applied to discriminate between malt
samples on the basis of the selected aldehydes in their volatile
pattern. Furthermore, PCA displayed good reproducibility of the SIFT
analyses and showed the high potential of SIFT-MS for fast
classification of the different malt samples investigated. Knowledge of
these variations in headspace profiles among various malted barley
types, varieties, and harvest years is of great interest to the brewing
industry.
Jessika De Clippeleer obtained her M.S. degree in food technology,
specialization food chemistry, from Wageningen University, The
Netherlands, in 2003, after receiving an M.S. degree in industrial
engineering in biochemistry at KaHo St.-Lieven, Gent, Belgium, in 2000,
and studying at Escola Superior de Biotecnologia, Universidade Católica
Portuguesa, Porto, Portugal, as an Erasmus student. She began employment
with KaHo St.-Lieven in 2003 as a food chemist in the meat laboratory
of the Biochemistry Department. In 2004 she joined the analytical
laboratory of the Enzyme, Fermentation and Brewing Technology Research
Group of KaHo St.-Lieven, where she started a Ph.D. study on beer flavor
stability and hopping technology in 2005. In addition to her Ph.D.
research activities, she is involved in several research projects and
lectures on biochemistry and food safety. Her research experience is in
the field of food chemistry, beer flavor stability, hop chemistry, and
malting. Her expertise is in principles, technology, and applications of
analytical chromatographic and mass spectrometric techniques.
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