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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

Citation:  Paper number  026181,  2002 ASAE Annual Meeting . (doi: 10.13031/2013.9793) @2002
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.

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