Phase behavior and synergistic gelation of scallop (Patinopecten yessoensis) male gonad hydrolysates and gellan gum driven by pH

BACKGROUND: Scallop P. yessoensis male gonads contain 81.7% protein. Scallop male gonad hydrolysates (SMGHs) are prepared by treating the male gonad of scallop with trypsin, which is a rich source of essential amino acids with the potential to be a protein supplement. Gellan gum (GG), as a typical anionic polysaccharide, can improve the textural properties of proteins. Complex polymerization can be considered the separation of two liquid phases driven by electrostatic interactions between oppositely charged biomacromolecules (proteins and polysaccharides) and is mainly affected by the pH of the solution. In detail, pH_c, pH_φ1, and pH_max are three critical pHs obtained during the complexation and coacervation processes, corresponding to the generation of the initial soluble complexes, aggregated coacervates, and the electrical equivalency with the maximum coacervates.

METHODS: The complexation and coacervation of SMGHs and GG were investigated via turbidimetric titration at different pHs (1-12) and biopolymer blending ratios (9.5:0.5-6:4).

RESULTS: Both pH_c and pH_φ1 exhibited ratio-independent behaviors with constant values at approximately pH 5.8 and pH 3.8, respectively. SMGHs/GG typically experienced three conditions, namely, mixed polymers, soluble complexes, and insoluble coacervates, with pHc and pHφ1 as boundaries. Overall, SMGHs and GG exhibited synergistic gelation under acidic conditions, with the storage modulus (G') increasing by approximately 42-, 696-, and 3422-fold and 99-, 550-, and 1.5-folds, respectively, and at pH 7, 5, and 3, compared with SMGHs and GG. As pH decreased from 7 to 3, the G' of SMGHs/GG gels increased by 21-fold, with initial viscosity η values increasing by 3.3-fold.

CONCLUSION: Thus, the SMGHs/GG gels could be potentially utilized as food formulations, such as thickeners and fat replacers, carriers for nutraceuticals and flavor compound embedments, and in food-grade packaging, contributing to the current need in the field of foods that could solve or bring a substantial improvement.