Flavour Binding by Solid and Liquid Emulsion Droplets - Food Colloids: Self-Assembly and Material Science - page 424

the crystalline fat. The goal of this work is to examine in more detail the
interactions between solid fat and aroma molecules in a model food emulsion.
29.2 Experimental
Unless otherwise stated, ingredients were purchased from the Sigma Chemical
Company (St. Louis, MO). Oil-in-water emulsions (40 wt% oil) were prepared
by mixing n-eicosane (Fisher Scientific, Springfield, NJ) with 2 wt% sodium
caseinate solution (containing 0.02 wt% thimerosal as an antibacterial agent)
using a high-speed blender (Polytron, Brinkmann Instruments, Westbury, NY).
The mixture was then recirculated through a twin-stage valve homogenizer
(Panda, GEA Niro Soavi, Hudson, WI) for several minutes at different
pressures (15-60 MPa) to achieve multiple passes through the valves. The
particle-size distribution of the emulsions was characterized by static light-
scattering (Horiba LA 920, Irvine, CA) using a relative refractive index of 1.15.
The initial emulsion was diluted with deionized water to produce a series of
samples with different oil contents, and aliquots (2 mL) were added to 20 mL
head-space (HS) vials.
Emulsified alkanes show deep and stable supercooling, 7 and so emulsions of
either wholly liquid droplets or wholly solid droplets were prepared by either
cooling the vials directly to 301C, or by cooling to 101C to induce homogeneous
nucleation and then reheating to 301C. The solid and liquid droplets were stable
at this temperature over several weeks - no change in measured particle size, no
apparent creaming and no change in the droplet melting or crystallization
enthalpy.
A stock aroma mixture was prepared from ethyl butanoate (EB), ethyl
pentanoate (EP), ethyl heptanoate (EH) and ethyl octanoate (EO) mixed in a
volumetric ratio of 1:2:20:20 and diluted in an equal volume of ethyl alcohol.
Aliquots of the stock mixture were added to the vials so that the final
concentrations of aroma compounds EB, EP, EH and EO in the emulsion
were 10, 20, 200 and 200 mLL 1 , respectively. The vials were sealed with
poly(tetrafluoroethylene)/butyl rubber septa and equilibrated at 301C for at
least 1 h prior to analysis. Other measurements showed that the values reached
after 1 h remained constant for over a week, suggesting the samples had
reached equilibrium after this time.
Following equilibration, a sample of the head-space gas (1 mL) was with-
drawn using an autosampler (Combi-Pal, CTC Analytics, Carrboro, NC, USA)
and injected into a gas chromatograph (Agilent 6890, Agilent Technolo-
gies, Palo Alto, CA, USA) operating in splitless mode and equipped with a
DB-5 capillary column (30 m 0.32 mm i.d. with 1-mm film thickness) and a
flame ionization detector. The operating conditions were as follows: carrier
hydrogen flow-rate ¼ 2.0 mL min 1 ; inlet temperature ¼ 2001C; detector
temperature ¼ 2501C; oven program 301C for 1 min, increasing at 351C
min 1 to 2001C, and constant at 2001C for 2 min. The static head-space
concentrations were determined from peak areas using a standard calibration