Caseinolytic activity of fruit extract from Opuntia ficus-indica on bovine, caprine, and ovine sodium caseinates

The rates and extents of hydrolysis of α_S- and β-caseins from bovine, caprine, and ovine sodium caseinates produced by an enzymatic extract of the fruit of Opuntia ficus-indica, (L.). Miller were evaluated and compared with those produced by a commercial animal rennet. A mechanistic model based on a pseudo-first-order enzymatic reaction, in the presence of first-order deactivation of the enzyme, was postulated and successfully fitted to the experimental data. The animal rennet exhibited higher enzymatic efficiency than the fruit extract, irrespective of the source (i.e., bovine, caprine, or ovine) and the type (i.e., α_S- or β-casein) of substrate. The enzymatic efficiency (k_cat/K_m) for α_S-casein ranged from 72 to 220 and from 43 to 65 L g^-1 h^-1, and for β-casein from 242 to 742 and from 55 to 164 L g^-1 h^-1, for the animal rennet and the enzymatic extract of O. ficus-indica, respectively. Finally, it was observed that β-casein from caprine and ovine caseinates was degraded by O. ficus-indica faster than its α_S counterpart, but the reverse was observed for bovine caseinate.