Technology/IT ¦ IDM
March/April 2022 ¦ international-dairy.com · 43
of the foamed matrix leads to bubble collapse. The aroma release
from the foamed matrix is compared to the unfoamed matrix,
which serves as a reference.
In the mouth model, the temporal increase of the aroma concentration
in the headspace above the matrix (= aroma release),
which was initially almost free of aroma molecules, was determined
using a combined method of solid-phase microextraction,
gas chromatography and ion mobility spectrometry (Thomas et al.,
2021).
Exemplary release curves of two aroma compounds are shown:
More methyl salicylate was released from the unfoamed matrix
than from the foamed matrix (Fig. 2 A), but less 2-dodecenal
(Fig. 2 B), while some aroma compounds showed no significant
difference in release (Thomas et al., 2022).
To which of these categories the aroma compounds belonged
could be explained by their solubility behavior in water or octanol
(log P value). Foaming increased the release of the highly hydrophobic
aroma substances (log P > 3, e.g. 2-dodecenal, limonene)
and decreased that of aromas exhibiting medium hydrophobicity
(log P = 2 – 3, e.g. methyl salicylate, ethyl butanoate, camphor).
Hydrophilic aroma compounds (log P < 2, e.g. diacetyl, ethyl vinyl
ketone) were not affected in their release by foaming.
In contrast, volatility of the aroma substances did not play a
role in aroma release from the milk matrix, which is a new finding.
For example, limonene (p0 = 2.07 hPa) is significantly more volatile
than 2-dodecenal (p0 = 0.01 hPa), but both aroma substances
exhibit comparable release behavior from the foamed model milk
matrix.
For coffee crema, a different picture was reported: the higher
the volatility of the aroma substance, the more aroma substances
are released during foam collapse (Dold et al., 2011). Hydrophobicity
did not play a role. It can therefore be assumed that the release
of aroma substances in the oral cavity (as well as the aroma partition
in equilibrium) is determined by the composition of the food
matrix.
In the case of a foamed fat-free milk matrix, the interface of
the gas bubbles is stabilized by hydrophobic regions of the milk
proteins, possibly accompanied by a conformational change. These
hydrophobic regions of the proteins are thus available to a lesser
extent for interactions with aroma compounds. Therefore, the
aroma substances that interact with hydrophobic regions of the
proteins in the unfoamed matrix (reference) have fewer interaction
partners available in the foamed matrix and are released to
a greater extent. Aroma substances of medium hydrophobicity
showed a different behavior, as they were even bound more by
Aroma partition
in equilibrium
Package opening
→ Mass transfer
Oral processing
→ Deformation,
heat and mass transfer
Dynamic aroma release
Figure 1: Physical processes during aroma release in the mouth
Ortho-
nasal
Retro-
nasal
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