Exploring the effect of roasting and ultrasound treatment on the emulsifying properties and oxidative stability of flaxseed gum-stabilized oil-in-water emulsions

The current study investigated the effects of microwave roasting of flaxseed, combined with ultrasound-assisted emulsification as a dual-modality approach to enhance the techno-functionality of flaxseed gum as a natural emulsifier. The interfacial microstructure of flaxseed gum was characterised using atomic force microscopy (AFM) while the oil-water interface of flaxseed gum was examined by cryo-scanning electron microscopy (cryo-SEM). In addition, the internal structure of the emulsions was analysed using small-angle X-ray scattering (SAXS). The findings indicated that gum from roasted flaxseed had a notable impact on reducing the tension (6.42 mN/m) in the oil-water interface in comparison to lecithin (control) (17.44 mN/m). The emulsion stabilized by gum from roasted flaxseed using ultrasound-assisted emulsification (RS) led to a significant reduction in droplet size from 1.684 μm for emulsion stabilized by gum from non-roasted flaxseed without ultrasound-assisted emulsification (E) to 0.279 μm for RS and a high absolute surface charge value of 58.84 mV (p < 0.05) in comparison to E with an absolute value of 38.99 mV (p < 0.05). Emulsion stabilized by gum from non-roasted flaxseed using ultrasound-assisted emulsification (ES) and RS exhibited a heterogeneous microstructure with dense and clustered networks as shown from cryo-SEM. The physicochemical shelf-life test demonstrated that RS exhibited sedimentation stability and delayed lipid oxidation compared to other emulsions after one month of storage at +4°C. These findings suggest that ultrasound emulsification combined with microwave roasting of flaxseed prior to gum extraction can enhance the emulsifying properties and oxidative stability in oil-in-water emulsions for food applications.