Acidic and rennet coagulation of pea and casein mixed emulsions: A microscopic look at the rheology of curd formation

This study investigates the gelation behaviour of emulsions composed of micellar casein isolate (MCI), pea protein isolate (PPI), and rapeseed oil via acidic or enzymatic coagulation for the use in hybrid cheesemaking. With increasing demand for more sustainable dairy alternatives, hybrid systems composed of dairy and plant ingredients offer a promising route to reduce carbon footprint while preserving desirable textural properties. Emulsions with varying MCI:PPI ratios were pre-heated and gelled using glucono- δ -lactone (GDL) or rennet. The rheological properties of the gels were then assessed by small amplitude oscillatory shear (SAOS) while the microstructure of the gels were investigated by quantitative image analysis of confocal micrographs. Further, the oil droplet distribution of the emulsions prior to gelation were investigated using laser diffraction. Results revealed that acid-induced gels exhibited higher elasticity with increasing PPI content but lower critical strain values (CSV) indicating brittleness. Conversely, rennet-induced gels showed both increasing elasticity and CSV for increasing MCI fractions. Oil droplet size and distribution were found to correlate with gel elasticity where higher gel elasticity corresponded with smaller droplets in a more cohesive network. In general microscopy revealed that MCI forms a fine, interconnected network, while PPI aggregates into larger domains, with this effect being less pronounced in the acidic gels. These findings highlight the interplay between plant and dairy proteins in curd formation and demonstrate how the ratio of these and the gelation process can be used to tailor mechanical and structural properties, contributing to the development of more sustainable dairy alternatives. Pea-casein gels show distinct rheology under acid vs rennet coagulation Mixing casein and pea proteins show an antagonistic effect on gel structure Acid gels with more pea protein are more elastic but break under low strain Gelation could be achieved using rennet even at 30% casein Pea to casein ratio affected the oil droplet size both in emulsions and gels Casein gels have a dense and tight network under both acidic and enzymatic conditions