An adsorption effect on the gel strength of dilute gelatin-stabilized oil-in-water emulsions

Abstract

Abstract:The incorporation of emulsion oil droplets into a gelatin gel leads to an initial increase in shear modulus at 25 ~ for a gelatin concentration of 8 wt % but an initial decrease for a concentration of 5 wt %. The latter resuIt is consistent with a net lowering of the gelatin concentration available for gelation in the aqueous phase due to adsorption at the oil-water interface.Key words: Gelatin, emulsion, gel, shear modulus, adsorption.Incorporating filler particles into a gelatin gel matrix normally has the effect of increasing the gel strength [1,2]. It is not obvious, however, that this will always be the case for weak gelatin gels in which a substantial proportion of the protein may become adsorbed on the particles and hence be unavailable for bulk-phase gelation. In this Note, we predict that under certain conditions a minimum should be observed in a plot of gel strength against particle volume fraction, and we test the theory against shear modulus data on dilute viscoelastic oil-in-water emulsions in which gelatin acts both as an emulsifier and a gelling agent.The shear modulus G of a rubberlike network containing randomly-distributed filler particles can be written as [3]where Go is the modulus of the unfilled network, ~ is the particle volume fraction, and kl, k2, etc., are constants. The dependence of the gelatin gel elasticity on polymer concentration can be represented by the equationwhere K1 is an elastic constant, w i is the weight fraction of free (unadsorbed) polymer, and wc is the critical polymer concentranon for the onset of gdation. In a gelatin-stabilized emulsion, the weight W 970 fraction of adsorbed protein on the oil droplets is given by wa = 6FgR/Odv s, (3) where 0 is the oil density, F is the areal concentration at the oil-water interface, and dvs is the mean droplet diameter defined by dvs = ~i nid3i/~i hid2 (4) for a dispersion containing ni droplets of diameter di.Taking w = wf + wa as the total concentration of gelatin in the whole emulsion, we obtain the following expression for the emulsion shear modulus to order ~2:The parameter K2 is given by K2 = 6r/o(w -we)&. (6) Differentiation of equation (5) shows that, if a minimum does occur in a plot of G versus ~, the volume fraction at the minimum will be Cmin ---~ (2K2 -hl)/2 (K22 + k2 -2h,K2).(7)

Microstructure and elastic modulus of phase-separated gelatin–starch hydrogels containing dispersed oil droplets

“…In all gels, there was an increase in G 0 with oil content and time. Differences in G 0 with 4 wt% oil were minimal, similar to observations by Dickinson, Stainsby, and Wilson (1985) who worked on 5 wt% gelatin oil-filled gels. Though addition of oil containing polysorbate 20 also led to large increases in rigidity, its presence reduced G 0 in comparison to the gels with no surfactant (Fig.…”

The effect of filler particles on the texture of food gels

“…For active filler particles, as in the case of gelatinbased emulsion gels, a droplet modulus higher than the modulus of the continuous phase leads to an increase in composite modulus as a function of oil content, and vice versa. This was confirmed in a study by Dickinson et al (1985), in which increasing shear modulus with increasing oil content for a gelatin emulsion was observed.…”

“…At low concentrations of gelatin, this effect can be significant, with decreasing shear modulus and even a potential loss of gelling ability at higher oil concentrations (Dickinson et al, 1985).…”

Impact of Protein Gel Porosity on the Digestion of Lipid Emulsions

“…At gelatine concentration higher than 2.5 wt%, aggregation of emulsion droplets was visible which could be related to the higher storage modulus of the gelled emulsion compared to simple gelatine gels. Previous studies have shown that incorporation of particles or oil droplets could lead to an increase in gelatine gel rigidity depending upon the gelatine concentration (53,63). Oil droplets seem to contribute to the stiffening of the gel as they are mechanically connected to the gel matrix and so contribute to the gel strength (52).…”