Water Crystallization in Highly Concentrated Carbohydrate-Based Systems

Water crystallization was studied at a range of concentrations (20-60% solids) in sucrose and gum arabic systems. Increasing sucrose concentration reduced the nucleation temperature by 26 C compared to equilibrium values; crystal growth rates decreased by up 95% (from 8 x 10(-5) m/s with 40% sucrose to 4 x 10(-6) m/s with 60% w/w) for 7 degrees C supercooling, while addition of carboxymethyl cellulose (CMC)-higher viscosity-resulted in 40% slower growth rates (60% sucrose). Ice crystal shape changed from dendritic (-16 degrees C) to rounded edges (-24 degrees C) as the temperature decreased. For gum arabic, increasing supercooling (from 2 to 10 degrees C) resulted in faster growth rates (up to 3 times) for the 50% system, while the 60% solution showed rates <6 x 10(-6) m/s. Controlling water crystallization during freezing is critical in manufacturing of frozen/freeze-dried (bio)products, although little information is available on the behavior of concentrated systems (i.e., >40% solids). Despite presenting significant challenges (i.e., limited water availability and mobility), processing such concentrated systems could increase energy efficiency, as less water is processed. Results from this systematic investigation of crystal growth kinetics in concentrated carbohydrate systems demonstrate that crystal growth can be promoted despite kinetic limitations and reveal the potential to reduce energy demand during freezing/freeze-drying by processing less water.