High hydrostatic pressure- or heat-induced gelation of cowpea proteins at low protein content: Effect of calcium concentration

The effect of different calcium levels (10-40 mM) during protein denaturation on the characteristics of cowpea protein gels obtained by heating or high hydrostatic pressure treatment (HHPT) at low protein content (7.5%w/w) was studied. Calcium allowed the formation of self-standing gels. For the lowest levels of treatments (70 degrees C and 400 MPa) calcium avoided a complete protein denaturation, which in turn resulted in weak matrices. For the highest levels (90 degrees C and 600 MPa) the complete protein denaturation in the presence of calcium allowed that this ion strengthened the matrices by establishing associations between exposed reactive sites. For HHPT, hardness and elastic module increased for each increase in calcium concentration, while for heating a plateau was reached from 15 mM. Differences in interactions that stabilized aggregates (more hydrophobic ones for heating and more calcium bridges for pressurizing) could explain the differences between heat-and HHPT-induced gels. Most of the gels belonged to the aggregate type, which entails opacity and low water holding capacity.