EFFECT OF LOCUST BEAN GUM AND KONJAC GLUCOMANNAN ON THE CONFORMATION AND RHEOLOGY OF AGAROSE AND KAPPA-CARRAGEENAN

Mixing with locust bean gum (LBG) induces obvious gel-like character i n very dilute solutions of K+ kappa-carragenan (<0.01 w/w in 100 mM KC l). At higher concentration (0.085%), addition of LBG (0.036%) gives a shoulder on the high-temperature side of the DSC (differential scanni ng calorimetry) exotherm associated with the carrageenan disorder-orde r transition, with an accompanying increase in gelation temperature an d enhancement in gel strength (storage modulus, G'). On substitution o f LBG by konjac glucomannan (KM) the shoulder in DSC converts to a dis cernable peak. Van't Hoff analysis of optical rotation data indicates that the high-temperature thermal processes could arise from associati on of LBG or KM chains to the carrageenan double helix as it forms, wi th the main transition at lower temperature corresponding to ordering of surplus carrageenan. With kappa-carrageenan in the nongelling tetra -menthylammonium salt form, addition of LBG causes no detectable chang e in DSC; rheological enhancement high concentration (1% w/w) is limit ed to development of a very tenuous network, and in dilute solution a decrease in viscosity is observed. Agarose shows only a very slight in crease in the disorder-order transition temperature on addition of KM, and it shows no detectable change in DSC; rheological enhancement at high concentration (1% w/w) is limited to development of a very tenuou s network, and in dilute solution a decrease in viscosity is observed. Agarose shows only a very slight increase in the disorder-order trans ition temperature on addition of KM, and it shows no detectable change with LBG. These observations are interpreted as showing that efficien t bing-helices, but that extensive aggregation restrict synergistic in teraction by competition with heterotypic association. (C) 1995 John W iley & Sons, Inc.