Unexpected phase behavior of amylose in a high solids environment.
The purpose of this paper is to present and rationalize data concerning the structural behavior of amylose in the presence of glucose syrup. Observations were obtained by the experimental methods of small-deformation dynamic oscillation on shear, modulated differential scanning calorimetry, and scanning electron microscopy. In contrast to industrial polysaccharides that undergo readily a coil-to-helix transition (e.g., agarose, deacylated gellan, and kappa-carrageenan), amylose holds its structural characteristics unaltered at low and intermediate levels of glucose syrup. This is followed by an early phase inversion from a polysaccharide to cosolute dominated system at levels of solids above 70.0%, as compared to industrial polysaccharides that can dictate kinetics of vitrification at a solid content as high as 90.0% in the formulation. Additional viscoelastic "anomalies" include a clear breakdown of thermorheological simplicity with data exhibiting two tan delta peaks in the passage from the softening dispersion to the glassy state. Besides phenomenological evidence, mechanistic modeling using the combined framework of the free volume/reaction rate theories argue for two distinct glass transition temperatures in the mixture. It is proposed that the amylose/glucose syrup/water system does not reach a state of molecular mixing, with the morphological features being those of a micro phase-separated material.
Shrinivas
Preeti
P
Department of Chemistry, National University of Singapore, Singapore.
Kasapis
Stefan
S
D000688:Amylose / Q000032:analysis* / Q000737:chemistry*; D003080:Cold Temperature; D004548:Elasticity; D005950:Glucose Solution, Hypertonic / Q000032:analysis / Q000737:chemistry; D006358:Hot Temperature; D044367:Phase Transition; D012212:Rheology / Q000379:methods
D005950:Glucose Solution, Hypertonic; D000688:Amylose