Stability and rheology of egg-yolk-stabilized concentrated emulsions containing cereal β-glucans of varying molecular size

The effects of barley and oat β-glucans on rheological and creaming behaviour of concentrated egg-yolk-stabilized model emulsions were investigated. Four polysaccharide preparations were used, two from each cereal; one sample with high and one with low molecular weight, i.e. the molecular weights were alike in pairs (110×103 and 40×103, respectively). In order to elucidate the mechanism of action of β-glucans in emulsions, Tween 20-stabilized emulsions were also examined. Tween 20 enhances neither the continuous phase viscosity nor the interactions between the droplets, so the changes could be easily attributed to β-glucans. It appeared that the low Mw β-glucan samples stabilize emulsions against creaming by means of network formation in the continuous phase while their high molecular weight counterparts enhance the viscosity of the continuous phase. Comparison of dynamic rheological tests between a reference emulsion without β-glucans and emulsions containing β-glucans showed that the polysaccharides largely affects the viscoelastic behaviour of the emulsion. Ageing of β-glucan-containing emulsions did not affect significantly the viscoelastic properties except for the emulsions containing low Mw β-glucans extracted from oat. Interestingly, all emulsions containing β-glucans creamed approximately the same after 30 days of storage regardless which preparation was used. The egg yolk constituents seemed to play a dominant role on the viscoelastic and the creaming behaviour of the emulsions, i.e. the viscoelastic behaviour was further enhanced and this could not only be attributed to the presence of the β-glucans but also to the stronger interactions between the oil droplets. Ageing did not affect the viscoelastic properties of β-glucan-containing emulsions while the reference emulsion, prepared only with egg yolk, showed a decrease in the value of storage modulus. The former could be interpreted as a steady consistency of the product during storage independent of the creaming behaviour. The creaming behaviour varied among the samples with the high molecular weight β-glucans from oat showing the highest stability