In this study, the free anthocyanin content in pectin controls
prepared at 5 mg/mL concentration were measured (data not
shown).WSF control had a high amount of 12.5 lg/mL free anthocyanin
content, and CSF and NSF controls contained trace amount
of free anthocyanins. Both dialyzed WSF supernatant and freeze
dried WSF had a purple color. Freeze dried CSF was white, but
was pink when dissolved in aqueous solution. Both dialyzed NSF
supernatant and freeze dried NSF had a brown color. Since anthocyanin
is the major pigment in the blueberry fruits, the color of the
pectin-rich fractions was most likely contributed by anthocyanins.
AIS prepared from freeze dried blueberry powder was washed with
ethanol and acetone to remove free pigments and sugars. All
pectin-rich fractions were extensively dialyzed against deionized
water in dialysis tubing with 6–8 kDa molecular cutoff. Most
anthocyanin pigments were removed during AIS preparation, since
organic solvents are used for anthocyanin extraction (Bakker et al.,
1997; Chen & Camire, 1997). It was expected that any residual free
anthocyanin would be removed during dialysis. This suggests there
may be tightly bound anthocyanin pigments on blueberry pectinrich
fractions. The natural anthocyanin may bind tightly on the
surface of pectin-rich fractions through hydrogen bond and/or
hydrophobic interactions, similar to staining mechanisms between
natural colorants and cotton