Effect of counterions on the water sorption and glass transition properties of maltobionate salts

Abstract

AbstractThe purpose of this study was to clarify the effect of counterions on the water sorption and glass transition properties of maltobionate salts. Sodium maltobionate (NaMb), potassium maltobionate (KMb), and magnesium maltobionate (MgMb2) were employed, and the values for calcium maltobionate (CaMb2) and maltose were taken from the literature. The water sorption isotherm of the samples was characterized using the Guggenheim-Anderson-de Boer model. The glass transition temperature (Tg) and freeze-concentrated glass transition temperature (Tg’) were evaluated by differential scanning calorimetry. The effect of water content on the Tg was analyzed using the Gordon-Taylor model. The order of the anhydrous Tg values of maltobionate salts was: KMb < NaMb < maltose < MgMb2 < CaMb2. The anhydrous Tg of the divalent cation forms (MgMb2 and CaMb2) was much higher than that of the monovalent cation forms (NaMb and KMb). The anhydrous Tg will be affected by the plasticizing effect and electrostatic effect of cations. The Tg depression induced by water plasticizing was greater for KMb than for the other maltobionate salts. The order of Tg’ values of freeze-concentrated maltobionate salts was: KMb < maltose < NaMb < MgMb2 < CaMb2. This trend was almost the same as that seen for anhydrous Tg, but the range of the Tg’ values (242.2–257.8 K) was much lower than that of the anhydrous Tg (346.9–421.3 K). The Tg’ appears to be affected by the strength of ionic interactions and amount of unfrozen water.