Physics And Chemistry Basis Of Biotechnology - De Cuyper - tiera.ru

Saskia M. Van Ruth
sampled, but when six different people were given the same solution (2-butanone in
water), a considerable variation in the aroma release profiles was observed,
In the beginning of the nineties, attention turned to analyses that concentrate the
volatiles and remove air and water from the sample prior to analysis. Linforth and
Taylor [44] compared expired air collected from the nose and mouth of people eating
foods onto lengths of capillary tubes, as well as cryotrapping, and trapping on solid
carbon dioxide and Tenax. Furthermore, Roozen and Legger-Huysman [45] developed
a similar technique for measuring aroma release in the mouth at various time intervals.
Delahunty et al. [46] have also reported a Tenax-based system for in-mouth
measurements of volatile release from cheese. The work above described aroma release
from foods in terms of a time-averaged aroma profile.
Time-intensity sensory analysis has suggested that the aroma profile changes
temporally, and attempts have been made especially to measure the release of
individual aroma compounds over short periods of time using instrumental means. Real
time analysis requires a detector capable of continuously monitoring compounds in air.
Several different systems have been developed to allow real time gas phase analysis
[42,47-49]. With atmospheric pressure chemical ionisation compounds can be ionised
in air containing water vapour at atmospheric pressure and exhibits high sensitivity and
rapid response times. Taylor and co-workers modified an atmospheric pressure
chemical ionisation source of a mass spectrometer to allow the introduction of gas
phase samples. It is a soft ionisation technique, which adds a proton to the compound of
interest and does not normally induce fragmentation. Consequently compounds present
in the breath are monitored in selected ion mode, further enhancing sensitivity. Aroma
release from mints, strawberry-flavoured sweets [50], biscuits, sausages [5 1], gelatine
and pectin gels [52], as well as aqueous model food systems [53] have been studied.
Grab and Gfeller [54] adapted the technique for studies on strawberries.
6. Analitical techniques
6.1. INSTRUMENTAL CHARACTERISATION
6. I. I. Gas chromatography
Gas chromatography is a very powerful separation method in flavour science. Since the
early days of aroma research, more stable columns with greater separation resolution
are now commercially available. Gas chromatography became even more powerful and
useful with high resolution capillary columns used in combination with mass
spectrometers. Most of the extracts, distillates and headspace samples are nowadays
analysed by gas chromatography. For analysis of aroma compounds, gas
chromatographs are often combined to “chemical/physical” detectors, such as thermal
conductivity, flame ionisation, electron capture, flame photometric and mass
spectrometric detectors [55].
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