Effects of high pressure on amylases and starch in wheat and barley flours

Application of high pressures (to 800 MPa) to 25% ww slurries of barley and wheat flours indicated that pressures above 300 MPa caused an increase in the action of the α- and β-amylases due to starch gelatinisation, the apparent activity increasing with pressure to a maximum at 500–600 MPa. At higher pressures marked losses in action were observed. Pressure treatment caused inactivation of the isolated α- and β-amylases from malt barley and electrophoretic analysis suggested that disulphide bond-induced aggregation accompanied this loss in activity at pressures of 600 MPa and above. However, some loss of activity was seen at lower pressures, suggesting that aggregation was not the initial cause of inactivation. β-amylase from malt barley appears to be slightly more sensitive to pressure than α-amylase. Separate experiments showed that both pressure and heat gelatinised starch are more susceptible to amylase digestion than the intact granules.