Effect of polyols on the molecular organization and thermodynamic properties of low water content gelatin oligomers

- Studied the molecular packing and thermodynamic state of low water content gelatin.
- Reported changes in these quantities upon addition of water, sorbitol and glycerol.
- Water is a plasticizer, increasing the free volume, whilst reducing Tg of gelatin.
- Sorbitol and glycerol are packing enhancers, reducing the free volume and Tg.
- Results are key for optimizing matrix performance, e.g. for use in encapsulation.

We use Positron Annihilation Lifetime Spectroscopy (PALS) in conjunction with calorimetric measurements to investigate the effects of two polyols (sorbitol and glycerol) and water on the molecular packing and thermodynamic state of low water content gelatin matrices. Our calorimetric measurements show that water, sorbitol and glycerol all reduce the glass transition and dissociation/denaturation temperatures of the gelatin matrices. Glycerol has a more pronounced effect on the thermodynamic state of the matrices compared to sorbitol, while both polyols alter the molecular organization and water sorption behaviour in a similar way, despite the large differences in molecular weight. Our PALS measurements show that over the concentration ranges studied, both sorbitol and glycerol act as packing enhancers, causing similar reductions in the average hole size, vh, of the gelatin matrices. Finally, we observe complex changes in vh as a function of increasing level of hydration, showing two apparent regimes related to the state of water molecules in the gelatin matrices.

168