P-4
High-resolution hop essential oil analysis by using a comprehensive gas
chromatography methodology. Comprehensive multidimensional capillary gas chromatography (GCxGC) is a
comparatively new technique. This uses two columns connected in series with a
cryofocusing system at their junction and so allowing two-dimensional separation
of compounds that would normally coelute. Marriot and coworkers recently
introduced a new cryofocusing system achieving efficient pulsing of the first
column effluent, the Longitudinally Modulated Cryogenic System (LMCS). The LMCS
is a moving cryogenic trap that cryofocuses a portion of the eluting band and
then remobilizes the focused band segment into the second column. This allows
coeluting peaks from the first column to be zone compressed and pulsed rapidly
into the second column (of a different polarity than the first column) and
separated. Key attributes of the LMCS included high modulation speed, narrow
base widths of bands and up to column maximum temperature program. This new
technique delivers to the analyst both unmatched resolution capability and
increased detection sensitivity. In complex samples such as essential oils,
GCxGC has proven to give exceptional separation power. To gain the maximal
benefit from this powerful separation technology, it is necessary to have
appropriate data handling software. Indeed, the resulting chromatograms are in
three dimensions. The first and second dimensions are the elution times on the
first and second columns, and the third dimension corresponds to the FID
response. Because of the three-dimensional characteristic of the chromatograms,
quantitative analysis would require integration of the peak volumes instead of
the peak areas. To avoid shifts in the retention time, it is appropriate to
convert the retention times into Kovat indices using selected paraffins as
references. Available commercial software for contouring and three-dimensional
surface mapping were reviewed and one suitable package identified which allows
easy handling of the large data file with integration of peaks volumes and
inclusion of retention index for easy comparison of chromatographic runs. The
technique has been applied to the analysis of hop essential oils. The complex
nature of the oil components is readily displayed in a three-dimension
separation space, giving a fingerprint pattern that contains much subtle
information on the chemical class composition of essential oil samples.
Jean-Pierre Dufour. Studies: MSc., 1975-PhD., 1979 (Louvain). Research
fellow (Johns Hopkins University, School of Medicine, Baltimore, MD) 1979-1981.
Appointments: Catholic University of Louvain, Professor 1981-1993 (Head of the
Department of Brewery and Food Industries, 1987-1993); Universidade Catolica
Portuguesa, Escola superior de Biotechnologia (Porto, Portugal), visiting
Professor 1989-1994; University Senghor (Alexandria, Egypt), associated
Professor 1992-1995; Expert for EEC and UNIDO (Implementation of sorghum malt
for the production of lager beer in Africa) (1994-1996); University of Otago,
Dunedin, New Zealand, Professor (1995-present), Chairperson and Head of
Department of Food Science. Expertise: Flavour science, fermentation science and
technology, malting and brewing sciences, yeast biochemistry/enzymology. Active
member of EBC Brewing Science Group, ASBC, IOB, Institute of Food Technology,
American Chemical Society, New Zealand Institute of Food Science and Technology.
Vice-president and Fellow of the New Zealand Institute of Food Science and
Technology, New Zealand delegate to IUFoST.
JEAN-PIERRE DUFOUR (1), Ph. Marriott (2), E. Reboul (3), M. Leus (1), R. Bietson
(4), and P. Silcock (1). (1) Dept Food Sci, Univ Otago, PO Box 56, Dunedin, New
Zealand; (2) Chromatography and Molec Separations Group, Dept Applied Chem,
Royal Melbourne Inst Tech, Melbourne, Australia; (3) ENSBANA, Dijon, France; and
(4) HortResearch, Nelson, New Zealand.