Calcium addition to cowpea protein isolates induces changes on thermal properties and characteristics of gel obtained by thermal or high pressure treatments

Abstract

The effect of calcium addition (CaCh, 0 - 4 0 mM) on thermal properties and heatinduced(TT, 90 °C - 20 min), or high pressure-induced (400 or 600 MPa - 5 min) gelation ofcowpea protein isolate was analysed. The temperature of denaturation increased with increasedcalcium concentration, without changes in enthalpy of denaturation. The degree of denaturationafter TT or 600 MPa was 100% for any assayed calcium concentration. In the case of a 400 MPatreatment, a baroprotective effect of calcium was detected since denaturation degree decreasedfrom 87 to 35 % with increased calcium concentration from 0 to 40 mM. Calcium additionimproved gelation ability of protein dispersions (8 % w/w), the magnitude of this effect wasdependent on calcium concentration and on type and level of denaturation treatment. Thestrongest gels, characterized by small deformation rheology, were obtained after 600 MPa with40 mM CaCh. The gels obtained after 400 MPa exhibited a higher viscous behavior than thoseobtained with fully denatured proteins (TT or 600 MPa). Water holding capacity was function ofcalcium concentration and type of denaturation treatment, with the highest values observed ingels obtained with TT and low calcium concentrations. Gels were opaque and L* valuesincreased with increased calcium concentration, probably due to protein insolubilization. Ourresults indicate that calcium addition may be used to obtain cowpea protein isolate gels withlower protein concentration. The increase in calcium concentration increased G´ and G" butworsened water holding capacity.