The effects of alginate molecular structure and formulation variables on the physical characteristics of alginate raft systems

A study has been conducted in order to assess the effects of alginate molecular structure and formulation variables on alginate raft strength and dimensions. In addition, the use of texture analysis as a novel means of characterising alginate raft systems has been investigated. Five alginates of known molecular composition were used (LFR 5/60, LF 120M, LF 10/40RB, LF 20/200 and LF 200DL), while two gas-forming agents (sodium and potassium bicarbonate) and two divalent cationic salts (calcium carbonate and zinc carbonate) were studied. The effects of acid strength on raft formation was also investigated. II was noted that the inclusion of divalent cations and the use of the lowest molecular weight alginate sample (LFR 5/60) increased the volume of the resulting rafts. Texture analysis measurements allowed both the maximum breaking strength and the work involved during the rupture process to be quantified. Inclusion of divalent cations (particularly calcium) increased the raft strength, while inclusion of potassium carbonate resulted in stronger rafts than did sodium carbonate. Alginates with higher guluronic acid contents resulted in stronger rafts, with the exception of LFR 5/60 which yielded weaker rafts despite the high G ratio, probably as a result of the lower molecular weight of this material. Raft volume and strength increased with decreasing PH of the raft forming media. (C) 1997 Elsevier Science B.V.