An advantage of using preformed microbeads is that diffusional
losses do not occur, as riboflavin is diffusing from the surrounding
solution into the microbead. Interestingly, at ratios where both
methods overlap, between 0.5 and 1, the concentration of riboflavin
in the microbeads from both the internal and external methods
are similar. However, the principal advantage of the external method
is that higher ratios of riboflavin to protein can be achieved by
simply increasing the volume ratio of external solution to microbeads.
For the external method a maximum concentration of
100 mg/L of riboflavin in 10 ml of water was used, resulting in a
riboflavin concentration of 361 mg/L in the microbeads. The comparison
between the two methods shows that using blank microbeads
has significant advantages including achieving higher
concentrations of riboflavin in the microbeads and no diffusional
losses during crosslinking. Wells and Sheardown (2007) also reported
an absence of diffusional losses as a key advantage to using
blank alginate microbeads for encapsulation as well as the high
levels of encapsulation obtained. The external method is particularly
well suited to small molecules that would normally diffuse
out of the microbead during crosslinking. Additionally, producing
blank microbeads facilitates large scale production as the blank
microbeads can be sold as a ready-made encapsulation system
and subsequently loaded with a range of different bioactive molecules
e.g. insulin (Déat-Lainé et al., 2013). In the external method
the equilibrium concentration of riboflavin within the microbeads
is higher than that of the surrounding solution, suggesting an affinity
exists between the riboflavin and the microbead.