Ultrasound assisted vis-a-vis classical heating for the conjugation of whey protein isolate-gellan gum: Process optimization, structural characterization and physico-functional evaluation

In the present work, ultrasonic assisted synthesis and characterization of Maillard conjugates of whey protein isolate (WPI) and gellan gum (GG) was carried out and compared with the classical heating method. Conjugation was confirmed by FTIR, secondary structure, intrinsic fluorescence analysis, and degree of glycation (DG). The structural analysis revealed high protein unfolding by sonication confirming loss of alpha-helix content and exposing more amino groups to the conjugation reaction. Color change analysis confirmed that ultrasonication accelerated the initial stage of Maillard reaction but did not form the advanced Maillard reaction products. Ultrasonication gave higher DG in lesser time (17.22% in 60 min) than classical heating method (8.41% in 4 h). Physicofunctional properties such as pH and thermal stability, emulsifying activity index, emulsion stability index, foaming capability and antioxidant activity of WPI-GG conjugates prepared by ultrasonic treatment were superior to classical heating method suggesting ultrasonication as a potentially alternative method for Maillard conjugation. Industrial relevance: Improvising supplementary protein functionality by conjugation with food grade polysaccharides like gellan gum through ultrasonication could make the process more controllable and economical. The undesired browning can be inhibited in ultrasonic assisted conjugate synthesis and hence the overall acceptance of the final product can be increased.