BINDABILITY AND DIGESTIBILITY OF HIGH-PRESSURE-TREATED STARCH WITH GLUCOAMYLASES FROM RHIZOPUS SP

The effect of hydrostatic pressure on the bindability and digestibilit y of raw corn starch with two types of glucoamylase [EC 3.2.1.3] from Rhizopus sp., Gluc(1) and Gluc(2), was investigated in the range of 10 0 to 600 MPa. Pressurization of raw starch at 100 to 300 MPa for 1h ha d no detectable effect, whereas pressurization at higher pressures tha n 400 MPa markedly enhanced the bindability and digestibility with Glu c(1) and Gluc(2), especially with Gluc(2), which scarcely binds to raw starch and has much lower activity than Gluc(1) towards raw starch. T he binding constants K-s of Gluc(1) and Gluc(2) for the 400-MPa-pressu rized starch reached 16 and 1.6 X 10(5) M(-1), respectively, as compar ed with the K-s of 2.1 and 0.082 X 10(5) M(-1) for raw starch. The 500 - to 600-MPa-pressurized starch was digested by Gluc(1) and Gluc(2) at about 4.2 and 80 times higher rates, respectively, than raw starch. T hus, the high-pressure-treated starch was hardly distinguishable from high temperature (75 to 100 degrees C)-treated starch at least with re spect to behavior with the enzymes, although some difference was obser ved between these starches by scanning electron microscopy and differe ntial scanning calorimetry.