Effects of calcium and high pressure on soybean proteins: A calorimetric study

The effects of calcium and high pressure (HP) treatment on the thermal properties of soybean proteins were analyzed in soybean protein isolate (SPI), a β-conglycinin-enriched fraction (7SEF), a glycinin-enriched fraction (11SEF), and whey protein concentrate (WPC). For β-conglycinin, the temperature of denaturation (Td) decreased with up to 12.5 mM or 6.2 mM calcium in SPI and 7SEF, respectively. This parameter increased when calcium was more concentrated. The Td of glycinin increased for every assayed calcium concentration. The values of changes in Td (ΔTd) depended on calcium concentration and the proportion of β-conglycinin and glycinin in the samples. Activation energy decreased for glycinin in the presence of calcium. HP treatment promoted denaturation of β-conglycinin and glycinin. Calcium protected both proteins in SPI, 7SEF and 11SEF at 200 MPa, and protected glycinin in SPI and 7SEF at 400 and 600 MPa. Nevertheless, calcium increased the degree of denaturation of β-conglycinin in 7SEF at 600 MPa. In the absence of calcium, partially-HP-denatured polypeptides exhibited the same or lower Td than controls, whereas in its presence, they exhibited higher Tds than their respective controls.