New small endothermic peaks with hysteresis commonly observed in the differential scanning calorimetric study of biopolymer–water systems

Abstract New small endothermic transitions with remarkable hysteresis were found in many biopolymer–water systems including proteins and polysaccharides by using a high sensitivity differential scanning microcalorimeter. The transition temperatures are usually around 40°C for fresh samples and they shift to the temperatures from 20 to 60°C according to the preservation at various temperatures. The transition enthalpies per gram of water (Δ H w ) in the samples lie between 2 and 20 J/g water, and are not so diverse from species to species for the fresh biopolymer–water systems. The Δ H w decreases rapidly with the increase of water content of the samples. The remarkable narrowing of the band width of 1 H-NMR signals of lysozyme–water and starch–water systems were observed at the temperature ranges of the endothermic transitions. The band widths showed fine hysteresis corresponding to the hysteresis behavior observed in the DSC measurements. The endothermic transitions observed in the DSC measurements must be brought about by the release of the cooperative motion of water and the biological macromolecules.