Can the reaction blank be used to zero the spectrophotometer directly in the procedure for α-Amylase Assay Kit (Ceralpha Method) (K-CERA)?

You can zero the spectrophotometer directly with the blank. However, it is wise to know how high the blank is to ensure that the substrate is OK, i.e. the blank is usually 0.05-0.06. If it is above 0.1, it has probably been contaminated with some alpha-amylase enzyme.

Product Page (K-CERA)