Influence of the molecular-weight distribution of gelatin on emulsion stability

The influence of molecular-weight distribution of gelatin on emulsion stability was measured. Two different oils with different polarity were selected, tricrecylphosphate (TCP) as a polar oil and n-dodecane as an apolar oil. The gelatin molecular-weight distribution was varied by mixing hydrolyzed (containing mainly small, i.e., <95 kDa, molecules) and nonhydrolyzed lime bone gelatin (intrinsically composed of a mixture of various molecules almost all >95 kDa) in various ratios. The stability was measured using turbidity. The obtained gelatin molecular-weight-stability profile for TCP and n-dodecane at various sodium dodecyl benzene sulfonate (SDBS) concentrations was completely different. For TCP the best stability was obtained for gelatins characterized by an average molecular weight between 50 and 100 kDa and at a SDBS concentration between critical aggregation concentration (CAC) and critical micelle concentrations (CMC). For n-dodecane stability gradually improved after increasing the SDBS concentration and after increasing the molecular weight of gelatin. The influence of gelatin molecular weight on n-dodecane stability indicated that stability is achieved either by steric (gelatin molecular weight) or electrostatic (surfactant) protection. For TCP, an exquisitely balanced electrostatic and steric protection appeared to be essential for its stability. The contribution of electrostatic phenomena toward improving TCP stability was confirmed by zeta-potential measurements. Overall the type of stability mechanism seemed to depend not only on the type of oil and the molecular weight of the gelatin used, but also on the pH and the region of gelatin-surfactant interaction in which the system lay. The basic reason for the observed stability difference is the much weaker interaction of SDBS to hydrophilic TCP compared to hydrophobic n-dodecane. The improved TCP stability after increasing the amount of small gelatin molecules is likely to be the result of the accelerated interaction between gelatin and SDBS. An increase in steric and electrostatic hindrance is a possible explanation for these phenomena. (C) 2001 Academic Press.