Analyze functionality of polysaccharide stabilizers in frozen foods.

Polysaccharide stabilizers find use in frozen food systems to slow the process of ice recrystallization and the structural changes that occur during the product's frozen storage. Recrystallization negatively impacts water-holding properties of the product as it thaws, and it can also negatively impact textural characteristics when the product is consumed.

Ice cream is one product that utilizes polysaccharide stabilizers, but it is unique in that it is consumed frozen, so the size distribution of the ice crystals is of critical importance for textural quality. Understanding how these polysaccharides function and control ice crystal growth has been challenging, but is of importance to both finding and assessing new ingredients and to making modifications to existing products.

Various microscopic techniques can be used to explore the structure of polysaccharides, including specific staining with light, transmission electron microscopy and fluorescence microscopy. Polysaccharides are well-known viscosity enhancers in solution. This property is a result of their structure and their ability to interact.

Through microstructural analyses, additional phenomena are evident in frozen systems. These are relevant to polysaccharide functionality. The first is cryogelation, an inter-molecular interaction induced by freeze-concentration that sets up three-dimensional macromolecular structure. The second is incompatibility and phase separation with proteins present in the food system. This is also enhanced by freeze-concentration and adds a further element of structure. These phenomena are responsible for polysaccharide functionality in frozen systems.

Scientists at the University of Guelph studied the effect of stabilizers on the recrystallization of ice cream that experienced constant and fluctuating temperatures during storage. They determined polysaccharide stabilizers did not affect the initial ice crystal size distribution of model solutions or ice cream frozen in a batch process.

Investigators found that a constant storage temperature of -30 C did not affect the overall ice crystal size. This was probably because of the proximity of this temperature to the glass transition temperature of the unfrozen phase. Stabilizers did not affect the size distributions of the ice crystals because they did not affect the glass transition temperature.

Recrystallization caused by fluctuations in temperature seemed to be dictated by migratory recrystallization. A melt-refreeze process was most likely the predominant mechanism of recrystallization, and in this case, stabilizers had a measurable effect in controlling ice crystal size.

Further information. Doug Goff, University of Guelph, Department of Food Science, Guelph, Ontario N1G 2W1, Canada; phone: [phone]; fax: [phone]; email: [e-mail].