Food Chemistry

5.4 Interactions with Other Food Constituents 391

Fig. 5.34.Distribution of n-alkanols in the system
oil/water (according toMcNultyandKarel, 1973)

ity imposed by chain length increases. The va-
por pressure behavior is exactly the reverse; it
drops as the hydrophobicity of the aroma com-
pounds 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 solubil-
ity of 2-heptanone is higher in whole milk than

Fig. 5.35.Influence of the medium on 2-heptanone con-
centration in the gas phase (according toNawar, 1966).
2-Heptanone alone ( 1 ), in water ( 2 ), in skim milk ( 3 ),
in whole milk ( 4 ), in oil ( 5 ).cfl: concentration in liquid;
cg: concentration in gas phase (detection signal height
from headspace analysis)

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 com-

pounds, 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

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 prob-

ably 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)

cf(B)

(5.38)

where K=a single binding constant; andcf=

concentration of free aroma compound

molecules.

[BA]=K·cf·(B) (5.39)

Fig. 5.36.Sorption of volatilecompounds on proteins

at 23◦C (according toMaier, 1974).

Hexane ( 1 ), ethyl acetate ( 2 ), acetone ( 3 ), ethanol ( 4 ).

plus: maximal sorption,: after desorption