Scope and Limitations of Using Wax to Encapsulate Water-Soluble Compounds - Food Colloids: Self-Assembly and Material Science - page 110

7.4 Results

7.4.1 Wax Capsules Prepared by Technique 1
Some large capsules of varying size were made by preparation technique 1. They
were loaded with a 33% solution of citric acid. We monitored the leakage of citric
acid from these capsules as a function of time. 15 The experimental data presented
in Figure 3 clearly show the effect of particle size. The same graph shows the
results of model calculations using a short-time approximation of the Crank
model. The parameter values of the model were chosen as follows: D d ¼ 4.5
10 15 m 2 s 1 , as taken from Scheiber and Riederer, 11 j ¼ 0.4, and K O/W ¼ 22.
From Figure 3 we can see that the leakage rate is unacceptable for the 1-mm
size capsules over a typical storage period of a couple of weeks, whereas the
larger capsules are considerably more stable. The parameter values of the model
calculations are realistic for the given situation, as they lead to a reasonable fit to
the experimental data, which confirms the reliability of the theoretical approach.

7.4.2 Wax Capsules Prepared by Technique 2
A 20% W/O emulsion was made by preparation technique 2 using PGPR and
beeswax as 'emulsifiers'. This technique was developed to prepare the smallest
possible wax capsules in order to overcome any textural defects in foods
associated with the other preparation techniques. 15 The water-soluble fluores-
cent dye FITC was used as the model encapsulated compound.
The previously described emulsion was mixed with another emulsion of
similar composition, except that no wax and FITC were included. We used
confocal microscopy to monitor the leakage from the FITC-loaded droplets
into the 'empty' ones. The results are presented in Figure 4.

50

40

30

20

10

0

0 5 10 15 20

Time (weeks)

Figure 3 Leakage test results of wax capsules. Percentage of maximum citric acid leaked
out is shown as a function of time for various capsule sizes: & , 1 mm; J , 1.5
mm; n , 2 mm; , 4 mm; and +, 7 mm. Lines show results of model calculations
using a short-time approximation of the Crank solution for the corresponding
capsule sizes