MALT DIASTATIC ACTIVITY. PART II. A MODIFIED EBC DIASTATIC POWER ASSAY FOR THE SELECTIVE ESTIMATION OF BET A-AMYLASE ACTIVITY,TIME AND TEMPERATURE DEPENDENCE OF THE RELEASE OF REDUCING SUGARS

Ammoniumcitrate, sodium EDTA and ammonium oxalate were tested as possible inhibitors of α-amylase in the EBC diastatic power assay. A contact time of 90 min at a concentration of 0·1 M ammonium oxalate was shown to inactivate α-amylase completely in the enzymic malt extract while only very slightly enhancing β-amylase activity. The selective release of reducing sugars by β-amylase in the diastatic power assay was evaluated as a function of time using a p-hydroxybenzoic acid hydrazide assay and compared with that of the diastatic power procedure with the same colourimetric technique. The diastatic power results of eight different malts are well correlated with those of the β-amylase activity (r² = 0·98). In a linear regression model the diastatic power results at 20°C of the same malts correlated better with results obtained at 55°C (r² = 0·77) than with those obtained at 60°C (r² = 0·63). For the results of β-amylase activities we found r² = 0·86 for the relation between the activities at 20°C and at 55°C and r² = 0·92 for the relation between the activities at 20°C and 60°C. Since the temperature conditions (20°C) of the EBC-diastatic power assay do not correspond to those of brewing practice it is suggested that the activity of β-amylase as well as the malt diastatic power be evaluated at 55°C.