Abstract
The effect of different concentrations of kappa-carrageenan on the
gel strength, gelation kinetics, and gel microstructure of bovine
serum albumin (BSA) gels was investigated at different conditions
of pH and ionic strength with and without the addition of potassium
chloride. Two types of strengthening effects were observed: a major
strengthening effect at the isoelectric point of BSA and slightly
above, low ionic strength, and high carrageenan concentration (similar
to 0.4-1.0% (w/v)); and a minor strengthening effect at higher pH
and all ionic strengths at lower carrageenan concentration (similar
to 0.2-0.4% (w/v)). The liquid that could be removed from the gels
by centrifugation had a lower carrageenan concentration than the
original gels at low pH and ionic strength, suggesting associative
phase separation. The gelation kinetics of these gels differed from
that of purr BSA or carrageenan gels, suggesting strong interactions
between the polymers. At high pH or ionic strength, the gel centrifugates
were enriched in carrageenan, and the gelation and melting of carrageenan
could be observed in the heat denatured BSA-kappa-carrageenan gels
by dynamic oscillation measurements. These effects are explained
by segregative phase separation. The results also show that the presence
of potassium ions during the gelation of BSA is important for the
strengthening effect at associative conditions. This strengthening
effect was observed up to higher pH values when sodium ions were
partly; replaced by potassium ions, and vanished completely when
the potassium salt of carrageenan was replaced by the sodium salt.
This suggests that synergistic interactions are present between the
carrageenan and the BSA gel networks, but not between BSA and carrageenan
in the sol state. (C) 2000 Elsevier Science Ltd. All rights reserved.
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