Surface active gelatins were formed by covalent attachment of hydrophobic groups to gelatin molecules by reacting N-hydroxy-succinimide esters of various fatty acids (C4-C16) with the lysine groups. The surface activity was evaluated by emulsification and foaming properties, and by adsorption at the oil-water interface. It was found that, in general, the modified gelatins are more surface active than the native gelatin. The increase in hydrophobic chain length and the number of attached alkyl chains per gelatin molecule leads to a decrease in the emulsion droplet's size and to more stable emulsions. Adsorption isotherms, at the o/w interface, show much higher surface concentration, at saturation, of the modified gelatin than the native gelatin. The modified gelatins also have high foaming ability and a high foam stability, while the maximal foam activity is obtained by the C8 modified gelatin. The foaming properties of the surface-active gelatins were also compared to that of sodium dodecyl sulfate (SDS) and it was found that below the CMC of SDS, both foam activity and stability were higher for the modified gelatins. On the other hand, above the CMC the foam activity of SDS was higher, but the foam stability was lower than for C8-C16-modified gelatins.
- Zeta potential