Design and characterization of EGCG conjugated walnut protein cold-set gels for quercetin encapsulation

While heat treatment is a conventional method for the gelation of alkaline-extracted walnut protein isolates (AWPI), it can limit the incorporation of heat-sensitive ingredients. This study explored a novel approach to fabricate cold-set gels from epigallocatechin-3-gallate (EGCG) conjugated AWPI (AWPI-EGCG). EGCG conjugation effectively inhibited the thermal gelation of AWPI while promoting the formation of soluble aggregates upon heat treatment. AWPI-EGCG cold-set gels were then successfully fabricated through acidification with glucono-δ-lactone (GDL). The rheological study revealed that the storage modulus and yield stress of the cold-set gels were positively correlated with the GDL concentration and the EGCG conjugation degree. However, higher concentrations of GDL were associated with the reduced yield strain of the gels. Texture analysis indicated an increase in gel hardness with increasing GDL concentration, accompanied by a decrease in springiness. Microstructural examination by scanning electron microscopy revealed that the AWPI-EGCG cold-set gels with 0.3 % GDL exhibited smaller pores with thinner and smoother internal walls, while those with 0.9 % GDL exhibited relatively larger pores with thicker and denser walls. In addition, the AWPI-EGCG cold-set gels showed promising quercetin encapsulation capacities and controlled release properties.