Insights into the effects of ionic strength and oil saturation on the emulsifying capacity of silkworm pupal protein: Focusing on protein structural, interfacial adsorption, and thermal stability

The effects of two key factors (ionic strength and oil saturation degree) in protein-stabilised emulsions on the conformation, emulsifying behaviour, and emulsion stability of silkworm pupa protein (SPP) were investigated. The results showed that the structure of SPP was sensitive to ionic strength. As ionic strength increased from 0 to 0.40 M NaCl, the decrease in β-sheet structure and increase in random coil of SPP indicated a shift towards disorder in the protein structure. The decrease in surface hydrophobicity and solubility suggested that the protein may form aggregates in aqueous solutions. After oil phase incorporation, the fluorescence intensity of the SPP-stabilised emulsion increased, accompanied by a significant red shift in the maximum wavelength, suggesting that SPP underwent structural rearrangement at the oil-water interface. The emulsifying capacity of SPP decreased with increasing ionic strength, as evidenced by a significant increase in droplet size and a reduction in absolute potential. Compared with low-saturation soybean oil, the high-saturation cottonseed oil emulsion exhibited a higher absolute potential and smaller initial droplet size. The cottonseed oil emulsion remained stable over the 60 h observation period following heat treatment. Rheological analysis further demonstrated that the heat-treated cottonseed oil emulsion possessed a higher apparent viscosity and more pronounced solid-like behaviour. These findings reveal that high ionic strength impaired the emulsifying capacity of SPP by disrupting its structure, whereas saturated oils may compensate for this instability by forming a viscoelastic interfacial network. This study provides meaningful insights into the stabilisation mechanisms of SPP-stabilised emulsions. • High ionic strength drives the spatial structure of SPP to transform towards disorder. • High ionic strength impairs emulsion stability by inducing SPP aggregation. • High-saturated fatty acids reduce salt ion-induced destabilization of SPP emulsions.