The standard solution of ferulic acid showed an uncompetitive
inhibition (Supplementary data 3A), where the value of km and
Vmax decreased with the inhibitor addition, but the km/Vmax ratio
hardly changed (Table 3). Such behaviour differed from that of
the solutions of fermented and unfermented rice bran, which displayed
similar inhibitory behaviour (Supplementary data 3B and
C); where the km values decreased and Vmax values showed little
change with the inhibitor addition (Table 3). This behaviour indicates
a competitive inhibition (Whitaker, 1994), and therefore
the phenolic compounds are similar to the preferred enzyme substrate.
Although these solutions presented a greater ferulic acid
concentration, especially in the fermented extract solution, the results
show that the phenolic acids mixture influence the peroxidase
enzyme inhibition, indicating that phenolic acids present in
the extracts compete with substrate molecules for the active centre
of the enzyme.