Interactions in bovine serum albumin-calcium alginate gel systems

Young's modulus of heat-denatured gels of calcium alginate and bovine serum albumin (BSA) was determined and compared to the modulus of BSA gels conta ining sodium alginate and to pure BSA gels. Ionic strength, pH, and calcium concentration were varied. The BSA Ca-alginate gels were either prepared w ith D-glucono-delta-lactone (GDL) and CaCO3 to induce alginate gelation bef ore the gelation of BSA, or by soaking heat-denatured BSA/Na-alginate gels in a CaCl2 solution. BSA/Ca-alginate gels were stronger than BSA/Na-alginat e gels at all conditions, and stronger than pure BSA gels up to higher pH v alues and up to somewhat higher ionic strengths than BSA/Na-alginate gels. The strength of BSA/Ca-alginate gels was highly dependent on the strength o f the alginate gel. This was shown by variation of the calcium concentratio n and by soaking the gels in EDTA, NaCl, and CaCl2 solutions. When BSA/Na-a lginate or BSA/Ca-alginate gels prepared at optimum conditions were soaked in solutions of higher ionic strength or pH, no reduction in gel strength w as observed. Consequently, they were much stronger than gels that were prep ared directly at high pH or ionic strength. The results may suggest that th e alginate network in a BSA/Ca-alginate gel increases the effectiveness of electrostatic BSA-alginate cross-links or entanglements. However, other exp lanations are also possible. (C) 1999 Elsevier Science Ltd. All rights rese rved.