Hybrid yoghurt-like gels from Nannochloropsis oceanica and bovine proteins structured with glucono-δ-lactone: Rheological, physicochemical, and microstructural insights

This study developed and characterized set-type hybrid yoghurt-like gels by combining Nannochloropsis oceanica protein (NP) with milk protein concentrate (MPC). The proportion of NP in the NP–MPC hybrid yoghurt-like gel formulations was 25 %, 50 %, 75 %, or 100 % of the total protein content (4.2 % w/w), with 100 % MPC gel serving as the benchmark. The yoghurt-like gel-forming premix was acidified with 2 % (w/w) glucono-δ-lactone (GDL) to induce gelation while avoiding fermentation-related complications. Variations in the buffering capacity of NP–MPC blends modulated the rate of GDL-induced acidification, affecting gelation time and gel strength, as reflected by changes in storage and loss moduli. The lower buffering capacity of NP led to a faster pH drop and reduced gel strength, with lower moduli values observed in NP-rich formulations compared to the more robust networks formed in MPC-rich systems. Increasing the NP proportion decreased viscosity and hardness while increasing syneresis. Gelation during acidification significantly reduced the browning index and increased the whiteness index. Formulations containing 50–100 % NP displayed an olive-green color. Among the formulations, the 25 % NP (75 % MPC) sample exhibited gelation, microstructure, textural, rheological, and syneresis characteristics closest to those of 100 % MPC, indicating it as an optimal formulation. The NP-rich formulation also exhibited a consistency resembling pourable yoghurt. Overall, this study provides new insights into the development of yoghurt-like gels from dairy–algal protein hybrids, with potential to balance nutritional quality and sustainability.