DSC and TMA studies on freezing and thawing gelation of galactomannan polysaccharide

Abstract

Among various kinds of polysaccharides known to form hydrogels, locust bean gum (LBG) consisting of a mannose backbone and galactose side chains has unique characteristics, since LBG forms hydrogels by freezing and thawing. In this study, effect of thermal history on gelation was investigated by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA).Gel/sol ratio calculated by weighing method was found to be affected by sol concentration, freezing rate and the number of freezing and thawing cycle (n). Once LBG hydrogels are formed, they are thermally stable, although syneresis was observed when n increased. Dynamic Young's modulus (E') of hydrogels measured by TMA in water increased with increasing n and decreasing freezing rate.Non freezing water calculated from DSC melting peak of ice in the gel decreased with increasing n and decreasing freezing rate. Morphological observation of freeze-dried gels was carried out by scanning electron microscopy (SEM). The above results indicate that weak hydrogel having large molecular network structure transformed into strong gel with densely packed network structure by increasing n and decreasing freezing rate.

Physicochemical and antioxidant properties of Lycium barbarum seed dreg polysaccharides prepared by continuous extraction

“…The peaks for four LBSDPs were 72.42–156.94 °C, 93.49–201.41 °C, 91.95–166.30 °C, and 109.07–185.37 °C, respectively. It can be related with the structural difference between the polysaccharides as reported in the previous studies ( Xu et al, 2019 , Iijima et al, 2012 ). Previous studies confirmed that with the wider temperature range, the thermal stability of the substance was lowered ( Xu et al, 2019 , Ji et al, 2019 ).…”

Structural characterization and hypolipidemic activity of Gracilaria lemaneiformis polysaccharide and its degradation products

“…The differential scanning calorimetry (DSC) curve represents the rate of heat absorption or release of the sample, and the area surrounded by peaks or valleys in the curve reflects the change of heat, so DSC can directly measure the thermal effect of the sample in physical or chemical changes ( Iijima, Hatakeyama, & Hatakeyama, 2012 ). The endothermic peaks of GLP, GLP-HV, GLP-H and GLP-V appeared at 785.3, 716.8, 789.9 and 724.7 ℃, respectively, indicating the transformation of solid configuration of polysaccharide and its degradation products, and the phase structure did not change before and after degradation.…”

DSC and TMA Studies of Polysaccharide Physical Hydrogels

“…Locust bean gum 18,23,80) and cassia gum 24) whose chemical structure is found in Table 1 are rare examples that form gel via freezing and thawing. Among galactomannan shown in Table 1, locust bean gum and cassia gum form the gel by freezing and thawing, and in contrast, no gelation is observed for fenugreek gum, guar gum and tara gum.…”