Cold-set gels from fresh duck egg white for probiotic delivery and application in mayonnaise

Surplus fresh duck egg white (DEW) is a poultry by-product that is often discarded due to off-flavor and instability. Therefore, DEW was used in this study to develop cold-set protein gels as protein-rich edible matrices for probiotic delivery in mayonnaise. DEW mixtures (45 %, w/w) were adjusted to pH 11.0, preheated at 60-80 °C for 30 min, cooled, and readjusted to pH 9.0 to produce soluble protein aggregate dispersions. Preheating at 70 °C (SA70) yielded aggregates with the highest surface hydrophobicity and most uniform particle size distribution, which favored gelation. Gels were formed by glucono-δ-lactone (GDL)-induced acidification (0.50-1.00 %) at 4 °C, and higher GDL concentrations significantly increased gel hardness (P < 0.05). SA70 + 1.00 % GDL yielded the greatest hardness but lower cohesiveness and syneresis stability, whereas SA70 + 0.75 % GDL provided balanced texture and water-holding capacity and was selected for probiotic delivery. Entrapment of Bifidobacterium longum Bl-05™ in the optimized gels caused no loss of viability during gelation, with counts remaining above 6 log CFU/g for 14 days at 4 °C. When applied in mayonnaise, the encapsulated probiotics maintained >4 log CFU/g for 21 days under acidic conditions (pH ∼4.1) and significantly outperformed the unencapsulated controls (P < 0.05). These results demonstrate that DEW cold-set gels can function as protein-enriched edible matrices with probiotic-protective capacity. Such gels also represent a feasible protein-based system for the encapsulation and delivery of anaerobic probiotic strains such as B. longum, while providing a sustainable approach to upcycle surplus poultry-derived proteins into value-added functional ingredients for refrigerated acidic foods such as mayonnaise.