Glass Transition Phenomena in Dehydrated Model Systems and Foods: A Review

Abstract

It is interesting to observe the evolution of the science of the glassy phenomena by following its development to a highly specialized subject, especially one that cuts across several conventional fields, such as the subject of this review. The manuscript is written with several objectives in view. First, I have compiled some basic information on the nature of vitrification for investigators who aspire to develop such an understanding of the subject. Second, a straightforward enough, I hope, exposition of food scientists to the synthetic polymer approach is provided, which constitutes the cornerstone of advances in the molecular understanding of biological rubbers and glasses. Third, a critical discussion of conceptual schemes applied to the vitrification of foodstuffs via rheology and differential calorimetry is developed in order to highlight the current state-of-the-art in the field. Finally, certain needs for further theoretical and experimental advances are pointed out in the hope that these will stimulate a much wider use of this framework of thought to a wide variety of conditions.

Keywords:

• Glass transition
• Rheology
• Calorimetry
• Polysaccharides
• Gelatin
• Sugar
• Dried foods

ACKNOWLEDGMENTS

The author is grateful to his colleagues, Shyam Sablani and Shafiur Rahman, for encouraging him to work on the mechanical properties of dried fish and fruits, and for critical evaluation of this manuscript.

Notes

*Configuration can be considered as the arrangement of substituents in an asymmetric carbon atom. It defines which anomeric forms of sugar (α or β) are possible. Conformation describes those changes in ring shape that are possible when substituents rotate about a bond linking two carbon atoms (chair or boat conformations).

The mixture of 50% s+35% gs will crystallise at subzero temperatures.

, and , are the WLF constants at T ₀ and T _g , respectively; f _g is the fractional free volume at T _g ; α _f is the thermal expansion coefficient.

s≡sucrose; gs≡glucose syrup-the composition of glucose syrup refers to dry solids; de≡degree of esterification.

*The cooling rate was 1°C/min; †The cooling rate was 2°C/min.