2009_Book_FoodChemistry

5.4 Interactions with Other Food Constituents 391
in skim milk which, in this case, behaves as an
aqueous phase. When this phase is replaced by
oil (Fig. 5.35), 2-heptanone concentration in the
gas phase is the lowest.
Experiments with n-alcohols demonstrate that,
with increasing chain length of volatile compounds,
the migration rate of the molecules from
oil to water phase increases. An increase in oil
viscosity retards such migration.
5.4.2 Proteins, Polysaccharides
Fig. 5.34. Distribution of n-alkanols in the system
oil/water (according to McNulty and Karel, 1973)
ity imposed by chain length increases. The vapor
pressure behavior is exactly the reverse; it
drops as the hydrophobicity of the aroma compounds
increases. The vapor pressure also drops
as the volume of the oil phase increases, and the
odor threshold value increases at the same time.
This is well clarified in Fig. 5.35. The solubility
of 2-heptanone is higher in whole milk than
The sorption characteristics of various proteins
for several volatile compounds are presented in
Fig. 5.36. Ethanol is bound to the greatest extent,
probably with the aid of hydrogen bonds. The
binding of the nonpolar aroma compounds probably
occurs on the hydrophobic protein surface
regions. A proposal for the evaluation of data on
the sorption of aroma volatiles on a biopolymer
(protein, polysaccharide) is based on the law of
mass action. When a biopolymer, B, has a group
which attracts and binds the aroma molecule, A,
then the following equation is valid:
K = (BA)
(5.38)
c f (B)
where K = a single binding constant; and c f =
concentration of free aroma compound
molecules.
[BA]=K · c f · (B) (5.39)
Fig. 5.35. Influence of the medium on 2-heptanone concentration
in the gas phase (according to Nawar, 1966).
2-Heptanone alone (1), in water (2), in skim milk (3),
in whole milk (4), in oil (5). c fl : concentration in liquid;
c g : concentration in gas phase (detection signal height
from headspace analysis)
Fig. 5.36. Sorption of volatile compounds on proteins
at 23 ◦ C (according to Maier, 1974).
Hexane (1), ethyl acetate (2), acetone (3), ethanol (4).
□ plus : maximal sorption, : after desorption