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The glass transition temperature of frozen foods and its influence on stability during frozen storage: analysis in starch sugar systems
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Paper number 026181, 2002 ASAE Annual Meeting . (doi: 10.13031/2013.9793) @2002Authors: Dr. FERRERO CRISTINA, Dr. ZARITZKY NOEMI
Keywords: Glass transition temperature, starch-sugar systems, rheology, hydrocolloids
During frozen storage, food systems based on gelatinized starch undergo syneresis and texture changes
related to amylose and amylopectin retrogradation; these recrystallization processes can turn food products
unacceptable. By applying concepts derived from physico-chemistry of polymers to food systems, many diffusioncontrolled
deteriorative phenomena have been related to the glass transition temperature. More specifically, the glass
transition temperature of the unfreezable matrix, which contains maximum solute concentration (Tg), determines the
stability of frozen systems. Maintaining the storage temperature below Tg the diffusional deteriorative processes are
minimized because the frozen matrix is in the glassy state. The objective of the present work was to analyze the
influence of the simultaneous addition of sucrose and different hydrocolloids (1% xanthan gum, guar gum or sodium
alginate) on Tg, correlating microstructural changes to rheological behavior. Differential Scanning Calorimetry
determinations showed that sucrose leads to Tg values below 22oC.
Viscoelastic behavior of the frozen pastes was tested by oscillatory rheometry. An increase of the dynamic moduli G'
and G* after slow freezing and during storage at 18C (T > Tg ) was related to sponge formation due to amylose
retrogradation in starch-sugar systems. The addition of hydrocolloids prevented the sponge formation, however
certain textural damage was evidenced. Hydrocolloids addition was beneficial from the technological point of view by
decreasing textural damage during frozen storage at temperatures above Tg . The effect of the gums could not be
attributed to modifications in the glass transition temperatures but to the lower molecular mobility induced in the
rubbery state by increasing viscosity.
The storage of food at the usual commercial temperatures (T = -18oC, above Tg) affects the quality of sugar systems
without gums due to amylose and amylopectin retrogradation. However when hydrocolloids are included in the
formulations, the usual storage conditions allows maintaining acceptable textural attributes.