22-4

S. SABLANI and S. Kasapis. Food Science and Nutrition, Sultan Qaboos University, P. O. Box-34, Al-Khod, Muscat, 123, Oman

In the last ten years or so, there has been a growing realisation that much of the theory of the glass transition developed around synthetic polymers and diluted systems should be pertinent to the study of high solids foodstuffs. A central point of this approach is the distribution function of relaxation times, Fi, which determines the changes in viscoelasticity during the glass transition of synthetic systems.

In a parallel submission to IFT, we demonstrate that high sugar/polysaccharide mixtures are amorphous systems which undergo vitrification readily upon cooling. In the present work, we present evidence that the analysis of the distribution function is also applicable to biological glasses.

In doing so, the calculations of the distribution function were applied to the small-deformation dynamic properties of high sugar agarose, gellan and high methoxy pectin mixtures. The total level of solids was 85% with the polysaccharide concentration being between 0.5 and 1.0%. First-approximation calculations of Fi employed the time derivative of the experimentally measured storage and viscous modulus (G' and G", respectively), with the two traces converging at the theoretically slope of -0.5 predicted by Rouse and Bueche for synthetic systems. Second-approximation calculations were based on Fi, as derived by the first approximation, being a simple power function of relaxation times (texp(-m)). The slope m was measured at various points and used to derive correction factors for shifting the relaxation function to the second approximation.

Values of Fi calculated by G' and G" were brought into satisfactory agreement, particularly in the recorded portion of the glass-transition region of sugar/polysaccharide mixtures. Once the function Fi is determined accurately, it can be readily used for calculations of other viscoelastic properties such as the stress relaxation after application of sudden strain and the steady-flow viscosity of foodstuffs.