This method describes the determination of α-amylase in malt.
α-Amylase is primarily involved in the degradation of starch to dextrins, thereby causing liquefaction. Its activity in barley indicates the degree to which germination has occurred, and in malt, it helps predict the time required for iodine test to yield a negative result during mashing. For this reason, α-amylase is considered to be a characteristic indicative of the quality of malt. Microbial enzyme preparations can also be analyzed with reference to their α-amylase activity.
Malt intended for use in beer brewing or elsewhere in the food industry
Using a buffer solution, malt extract is produced, and then under defined conditions the extract is incubated on a specific substrate of BPNPG7 oligosaccharide (a p-nitropheny-maltoheptaoside blocked at the non-reducing end) in the presence of thermostable α-glucosidase. The α-glucosidase is initially unable to degrade the "blocked" oligosaccharide. Only when the oligosaccharide is hydrolyzed by the activity of the α-amylase (an endoenzyme) from the malt are the resulting fragments vulnerable to the enzyme. Then, they are quantitatively degraded to glucose and free p-nitrophenol by the α-glucosidase, which is present in excess.
Adding a weakly alkaline solution halts the enzymatic activity and simultaneously induces a color reaction. The absorbance measured at 400 nm is proportional to the activity of α-amylase in the sample.