Investigation of thermal decomposition as a critical factor inhibiting cold crystallization in amorphous sucrose prepared by melt-quenching

Abstract

Researchers have reported that freeze-dried (FreD), spray-dried (SprayD), and ball milled (BallM) amorphous sucrose exhibit cold crystallization, whereas melt-quenched (MeltQ) does not. Three main explanations have been proposed to account for the lack of MeltQ cold crystallization: absence of crystal nuclei, lower sample moisture content, and dissimilarity to the crystalline state. However, in light of recent research revealing the presence of thermal decomposition indicator compounds in MeltQ sucrose, but not in FreD and SprayD, it is our objective to determine if thermal decomposition is also a plausible explanation for the lack of MeltQ cold crystallization. To achieve this objective, the physicochemical characteristics and thermal behavior of freeze-dried melt-quenched amorphous sucrose (FreD-MeltQ) were compared to those of MeltQ and FreD. Despite similar physicochemical characteristics to FreD, FreD-MeltQ did not exhibit cold crystallization. Powder X-ray diffraction and total scattering pair distribution function analysis showed that MeltQ and FreD-MeltQ had a more similar local structure to one another than to FreD. The underlying cause of these structural differences appears to be the presence of thermal decomposition compounds, with MeltQ and FreD-MeltQ containing similar amounts of thermal decomposition indicator compounds (7–8% glucose, 0.5–1% fructose, 0.2% 5-HMF, and 0.5% 1-kestose) and FreD containing none. Based on this evidence, we assert that thermal decomposition is an additional factor that contributes to the lack of cold crystallization in MeltQ sucrose.