Application of thermal treatments to enhance gel strength and stability of highly concentrated crayfish-based emulsions

Abstract

Highly concentrated oil-in-water (O/W; 25:75 wt%) emulsions stabilized by crayfish flour (CF) have been subjected to thermal treatments in order to study potential enhancements on gel strength of the network structures formed among oil droplets, involving adsorbed and non-adsorbed protein segments. Application of in situ thermal treatments, monitored by Small Amplitude Oscillatory Shear (SAOS), may lead to remarkable changes in the gel strength of CF-based emulsions, depending on processing conditions. If the heating temperature is above a critical value, the exposition time being long enough, thermal energy eventually leads to coalescence of oil droplets and subsequent emulsion destabilization. This behaviour has been confirmed by Droplet Size Distribution (DSD) measurements. The pH exerts a strong influence on the evolution of viscoelastic moduli. Little changes are produced at alkaline conditions, whereas a noticeable enhancement is apparent at neutral and acid pH. Application of consecutive double thermal cycle confirms the reversibility of the reinforcement induced by the cooling stage. The results may be explained in terms of the balance between electrostatic forces (predominant at alkaline pH) and hydrophobic interactions that favour protein aggregation and crosslinking (over heating stages), as well as hydrogen bonding (at the cooling stage). In addition, the influence of gel strength enhancement on the subsequent improvement of emulsion stability has been investigated by applying thermal treatments in a thermostatic bath. A clear enhancement in emulsion stability is achieved by these thermal treatments, although its contribution is not enough to produce long-term stability and a combination with other stabilizing strategies should be developed.