Firmness of pressure-induced casein and whey protein gels modulated by holding time and rate of pressure release

The main protein fractions of milk, casein and whey protein, may react differently to processing due to their amino acid sequence and conformation and their ability to build up intermolecular covalent and non-covalent bonds. Gels made from solutions of micellar casein and whey protein isolate were induced by applying ultra-high pressure (600 MPa/30 °C). The pressure built up was held constant at 200 MPa min^?1, while the holding time of 0.15 and 30 min was varied as well as the pressure release rate (20, 200, 600 MPa min^?1). The firmness of the pressure-induced whey protein gel was essentially influenced by the degree of whey protein denaturation and determined by the amount of disulfide bonds stabilizing the gel microstructure. In contrast, the firmness of pressure-induced casein-based gels was mainly influenced by pressure release rate. A slow pressure release produced a rough and weak gel. A high release rate, however, caused a homogeneous microstructure to be formed that created a high level of firmness.