Evaluation of ionic calcium and protein concentration on heat- and cold-induced gelation of whey protein isolate gels as a potential food formulation for 3D food printing

3D food printing (3DFP) is an innovative food process, but developing foods with ideal printability can prove challenging. Whey protein isolate (WPI) gels can be difficult to print due to their rigidity. This study evaluated the cold-and heat-induced gelation properties of WPI for use in 3DFP. Initially, the effect of WPI concentration ([WPI]) (8-12% (w/w)) and ionic calcium concentration ([Ca2+]) (0-8 mM) was evaluated on the heat-induced gelation capability and thermal reversibility. Treatments were categorised into three groups: thermo-irreversible, thermo-reversible, and non-gelling. Non-gelling treatments were used for cold-induced gelation by mixing the denatured WPI solution with 150 mM Ca2+ solution. Thermo-reversibility and cold-induced gelation properties were assessed using oscillatory rheometry. Finally, thermo-irreversible gels (TIRG) were characterised using extrudability and texture profile analysis. The thermo-reversible gels had an unsuitable range of G' (5-60 Pa) and delta (40-60 degrees) for obtaining a self-standing object. Cold gelation using [WPI] = 10%, G' > 500 Pa and delta < 10<degrees>, may be suitable for 3DFP but requires an adapted extrusion-based 3D printer, i.e., co-extrusion, cooling or support bath. The extrusion force of TIRG decreased during heating and was mainly affected by [WPI]. Upon re-cooling, the force recovered (>85%) with the addition of [Ca2+] > 4 mM. TIRG using the following treatments [WPI]-[Ca2+] = 12% -2 mM, 11% -4 mM, and 10% -6 mM demonstrated good printability. Principal component analysis showed TIRG with low hardness, resilience, and extrusion force loss during heating are potentially suitable for 3DFP.