| Abstract: | Mixing with locust bean gum (LBG) induces obvious gel-like character in very dilute solutions of K+ κ-carrageenan (< 0.01% w/w in 100 mM KCl). At higher concentration (0.085%), addition of LBG (0.036%) gives a shoulder on the high-temperature side of the DSC (differential scanning calorimetry) exotherm associated with the carrageenan disorder-order transition, with an accompanying increase in gelation temperature and enhancement in gel strength (storage modulus, G′). On substitution of LBG by konjac glucomannan (KM) the shoulder in DSC cornverts to a discernable peak. Van't Hoff analysis of optical rotation data indicates that the high-temperature thermal processes could arise from association of LBG or KM chains to the carrageenan double helix as it forms, with the main transition at lower temperature corresponding to ordering of surplus carrageenan. With K -carrageenan in the nongelling tetra-methylaminonium salt form, addition of LBG causes no delectable change in DSC; rheological enhancement at high concentration (1% w/w) is limited to development of a very tenuous network, and in dilute solution a decrease in viscosity is observed. Agarose shows only a very slight increase in the disorder-order transition temperature on addition of KM, and it shows no detectable change with LBG. These observations are interpreted as showing that efficient binding of mannan or glucomannan chains requires some aggregation of the algal polysaccharide helices, but that extensive aggregation restricts synergistic interaction by competition with heterotypic association. © 1995 John Wiley & Sons, Inc. |
