The nature of the microbead/riboflavin interaction was
explained by examining the effect of calcium chloride on the E
(%) of riboflavin. As shown in Fig. 2 the E (%) of riboflavin increases
with increasing mass of microbead protein present in solutions of
riboflavin dissolved in water or in CaCl2. When 0.1 g of microbeads
on a protein basis or greater was added to the solutions of riboflavin,
significantly (p 6 0.05) higher levels of riboflavin encapsulation
occurred in the presence of calcium chloride.
If an electrostatic interaction were responsible for the affinity
between riboflavin and the microbead then the E (%) would be expected
to decrease in the presence of CaCl2 due to shielding of the
charges on the whey protein thereby preventing an interaction
with riboflavin. Egan (2012) examined the binding of a positively
charged amino acid histidine by blank whey microbeads. The mass
of bound histidine decreased with increasing ionic strength of the
histidine solution due to competition from other cations for binding
sites on the microbead. This suggested that in that case the
interaction between histidine and the microbead was mediated
by ions and was therefore electrostatic in nature. The results of
Egan (2012) are contrasting to those in Fig. 2, which indicates that
the affinity between riboflavin and the microbead is not electrostatic
in nature, as E (%) increased in the presence of calcium.