Flavour Binding by Solid and Liquid Emulsion Droplets - Food Colloids: Self-Assembly and Material Science - page 428

Clearly, some critical ratio of aroma compound to solid fat is necessary to
achieve this, as the same amount of aroma stock added to more concentrated
emulsions caused no observable change [Figure 2(b)]. Furthermore, when the
individual droplets were observed at a higher magnification ( 1000), the aroma-
free samples appeared to be solid spheres [Figure 2(e)], whereas in the presence
of added aroma an adsorbed layer, presumably composed of aroma molecules,
led to the formation of less regular shapes [Figure 2(f)].
It is not possible to make a direct comparison between the large droplets used
in the microscopy study and the smaller ones used in the head-space GC
analysis, as the smaller droplets could not be adequately observed microscop-
ically. Nonetheless, similar behaviour was observed when differential scanning
calorimetry (DSC) was used to compare the melting enthalpies of fine
n-eicosane droplets prepared with and without added aroma. Samples ( 15

mg) were sealed into aluminium pans and placed in the calorimeter (Perkin-
Elmer DSC-7, Norwalk, CT) alongside an empty pan as a reference. The
melting enthalpies of n-eicosane in five emulsions (d 32 ¼ 0.44 mm) with different
oil contents prepared with or without added volatiles were measured by first
cooling to 101C then reheating at 51C min 1 to 501C. The ratio of the two
enthalpies was used as a measure of the effect of the added aroma on the solid
fat content of the droplets. At high oil/aroma ratios (i.e., high oil volume
fractions) the melting enthalpy of the n-eicosane was unaffected by the presence
of the aroma compound; hence this means that almost all the n-eicosane
remained in the solid state. But at low oil/aroma ratios (i.e., low oil volume
fractions) the melting enthalpy of the samples containing aroma was much
lower than those prepared without added aroma compound, suggesting a much
lower solid content of n-eicosane in the former case) (Figure 3). This supports
the hypothesis that the n-eicosane can dissolve in the aroma compound if
sufficient of it is present and it is adsorbed to the droplet surface. Any successful
model must therefore account for both the effect of the aroma on the phase
behaviour of the crystalline phase and on the potential binding of the aroma to
the solid and liquid phases present.

B

29.5 Surface Binding and Droplet Dissolution Model
The effects of solid and liquid fat in the droplets on the aroma release properties
of the emulsion can be taken into account using a modified form of Equation (3),

þ K iw A s
K gw

1
K ge

¼ f o ð 1 f sf Þ
K go

þ ð 1 f o Þ
K gw

ð 4 Þ

;

where f sf is the solid fat content, i.e., the proportion of the total lipid in the
emulsion that is crystalline. We can write a mass balance for the EH, expressed
in terms of concentration c and volume V of both the gaseous and the emulsion
phases, as denoted by subscripts g and e, respectively:
V EH ¼ c e V e + c g V g . (5)