Determination of phytase activity in cereal grains by direct incubation.

In contrast to supplemented microbial phytases, considerably lower cereal phytase activities were found after application of an enzyme solution extracted in citrate/NaOH buffer (pH 5.5) for 1 h as compared with the direct incubation of the plant material. Differences between both methods obtained were 70% for wheat and spelt and 50% for barley and rye. The determination of phytase activity of a wheat sample by direct incubation was affected by the sample size and amount of substrate (Na-phytate) added. Optimal conditions are a maximal level of phytase activity of < or = 0.05 U incubated for 60 min in a buffered solution (citrate/NaOH, pH 5.5) with 10 ml of 32.6 mmol/l Na-phytate at 37 composite function C. Possible reasons for the differences between both methods and for the factors affecting phytase activity by direct incubation are discussed.