Rheological and microstructural characterization of lotus seed milks and their glucono-δ-lactone induced acid-set milk gels: 2. effect of oil addition

Abstract

In a recent paper (Li, Li, Zhao, Cui, & Hemar, 2023) we showed that it was possible to manufacture lotus seed milks (LSM) and to use Glucono-δ-lactone (GDL) to prepare LSM acid-gels. LSM milks are known to have a very low lipid content, thus here the effect of soya oil addition is investigated in order to understand how LSM fortification with oil can affect its viscosity, and the mechanical and structural properties of the acid LSM gels. The oil was homogenized under conditions which resulted in oil droplets sizes in the range 0.1–0.4 μm. Heating the emulsions (80 °C, 30 min) resulted in a slight increase in particle size due to coalescence. The viscosity of emulsions was quasi-Newtonian and increased markedly with the increase in oil concentration. This was explained partly by the adsorption of the LSM aggregates at the interface of oil droplets, which increases considerably the effective volume fraction of the oil droplets. LSM emulsions when acidified by GDL formed colloidal gels with oil droplets embedded in the protein network, where the syneresis decreased with oil concentration, suggesting that the oil droplets should be considered as active fillers. The gel strength increased linearly with the oil concentration, but with a higher rate for the unheated emulsions than the heated ones. This is due to the decrease in the oil droplets number because of coalescence. This study demonstrates that homogenization of oil into LSM offers a route to manipulate the physico-chemical properties of the LSM emulsions and their acid gels.