The rheological properties and phase transition temperatures of 1.0 or 2.0%
agarose, kappa- and iota-carrageenans in the presence of 0.0-2.0% starches
were investigated to understand the changes in these properties with the d
egree of gelatinisation, concentration, and swelling-solubility of coexisti
ng starches. Generally, the addition of completely gelatinised rice starch
resulted in significant decrements in maximal storage modulus (G(max)', an
index of the susceptibility of syneresis), initial rate of G' increase (dG'
/dt, an index of initial gelation rate), and gel-melting temperature (T-m)
of agarose composites. These decrements were closely correlated with the co
ncentrations of agarose and soluble starch in the continuous matrices (C-x,
C-red and C-x,C-st, respectively), and depending on the sample preparation
used. In kappa-canrageenan composites, the increased gelling temperature (T
-gel), G(max)', dG'/dt and T-m values were obtained by adding starches, whe
re the G(max)', and T-m values were significantly correlated with C-x,C- (r
ed) more than C-x,C- (st). The influences of the starches on the gel proper
ties, except for T-gel, of iota-carrageenan resembled those on the K-carrag
eenan. The gel strengths of all composites decreased by the addition of sta
rch. It is concluded that the interference of soluble starch, the exclusion
effect of swollen granules, the molecular incompatibility and the coupling
interactions in the matrices appeared to give certain influences on the ge
l properties of these composites. (C) 1999 Elsevier Science Ltd. All rights
reserved.