Viscoelastic properties of frozen starch-triglycerides systems
1997
Navarro, A.S. | Martino, M.N. | Zaritzky, N.E.
Dynamic rheological methods are useful to determine the stability of starch-based products submitted to different processing conditions. A dynamic oscillatory test covering a wide range of strain values was used to analyse the behaviour of corn and waxy starch (7 and 10% w/w) pastes with and without triglycerides (5% w/w) or xanthan gum (0.03%). The effect of freezing rate on the structure stability was analysed using a slow freezing rate of 0.3 cm/h and a rapid one of 31 cm/h. After slow freezing, dynamic parameters (G', G*, tan delta) showed an increase in the rigidity of the pastes and a structural breakdown with a marked stress decay compared with the unfrozen or rapid frozen samples. The linear viscoelastic range of starch pastes decreased after rapid or slow freezing, showing that the paste structure cannot resist large deformations without undergoing irreversible breakdown. Pastes with lipids showed an increase of the linear viscoelastic range and higher values of G' compared with the control without lipids. The presence of triglycerides in frozen starch pastes led to a decrease of the solid component G' of the starch pastes, in addition, a less fluid character after structural breakdown was observed as well. A minor increase in rigidity after slow freezing was observed in pastes with sunflower oil, as compared with pastes containing a shortening with a more saturated fatty acid composition.
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