Impact of Heat Treatment and Calcium Addition on the Coagulum Quality During Raw and Heated Cow’s Milk Coagulation Induced by GDL

Acid-induced coagulation of milk plays an important role in the production of dairy products with high quality. The gel texture is significantly affected by processing conditions such as heat treatment and mineral composition. This study examines the effect of moderate heat treatment applied at 65 °C for 5 min and ionic calcium supplementation (10 mM CaCl2) on coagulation at 30 °C for 180 min of cow’s milk induced by glucono-δ-lactone (GDL). A slow and gradual protonation was induced, reaching pH values of 4.3–4.5. Rheological analysis revealed an increase in G’ from 59.28 Pa for raw milk gel to 224.1 Pa after the addition of CaCl2. An inverse trend was observed for gel produced with heated milk after the addition of CaCl2. However, the gel produced from calcium-fortified heated milk showed G’ values of 136.7 Pa. Turbiscan analysis showed the highest TSI for gels made from heated milk. Scanning electron microscopy analysis indicates that raw milk gels supplemented with CaCl2 exhibit dense and homogeneous networks, while heat-treated GDL gels show more porous networks. Mid-infrared (3000–2800 cm−1, 1700–1500 cm−1, and 1500–900 cm−1) and fluorescence spectra revealed changes in protein–protein, protein–water, and protein–protein–lipid interactions throughout coagulation.