Conjugate of silkworm pupa protein and ellagic acid prepared by thermal‐assisted pH‐shifting process for improving its antioxidant and emulsion stability

The pH-shifting and thermal-assisted pH-shifting process was applied to fabricate the silkworm pupa protein (SPP) and ellagic acid (EA) conjugates (SPP-EA_TP). The result revealed that more binding sites of SPP were exposed after the thermal-assisted pH-shifting treatment, which increased the conjugation between SPP and EA. This conjugation enhanced hydrogen bonding and hydrophobic interactions between SPP and EA, increasing the random coil content while reducing α-helix structure, thereby improving the flexibility of SPP-EA_TP. The SPP-EA_TP conjugate has outstanding emulsification stability and antioxidant capacity. For example, SPP-EA_TP can effectively stabilize and protect the high internal phase emulsion (containing 74% fish oil fraction) from oxidation. Furthermore, the emulsion prepared by SPP-EA_TP exhibited an excellent shelf-life due to the formation of a more compact boundary layer, which effectively prevents droplet aggregation and isolation of fish oil from pro-oxidants in the continuous phase. These findings provide a novel approach to the valorizing of SPP. Furthermore, the conjugate between SPP and EA possesses the potential application as an effective emulsion stabilizer in the food industry. PRACTICAL APPLICATION: The oxidation of fish oil during transportation and storage attenuates its physiological activity, thereby severely limiting its potential utilization in functionalized food. Through the thermal-assisted pH-shifting process, the prepared SPP-EA conjugate exhibits outstanding emulsifying and antioxidant performance. For instance, the shelf-life of the high fish oil fraction emulsion is substantially extended as the conjugate is used as the stabilizer. Hence, the conjugate can be widely utilized as the antioxidant emulsifier to protect active substances from oxidizing in the functional food industry.