Structural changes associated with the inactivation of lipoxygenase by pulsed light

Pulsed light (PL) is a non-thermal technology able to inactivate enzymes. Lipoxygenase (LOX) causes enzymatic rancidity in some foods. This study aimed to determine the structural changes associated with the PL inactivation of LOX and used measurements of residual activity, temperature, spectropolarimetry, fluorescence, spectrophotometry, free sulfhydryl and carbonyl contents and electrophoresis. LOX inactivation was non-log-linear, with a slight temperature rise. PL significantly increased the concentration of carbonlys and free-sulfhydryls of LOX and caused loss of ellipticity and intrinsic fluorescence, a red shift in the intrinsic fluorescence peak and an increase in 1-anilino-8-naphthalenesulfonate fluorescence. The turbidity of LOX sample increased during inactivation and electrophoretic bands faded. Phase diagram analysis showed no evidence of formation of intermediates. In summary, the inactivation of LOX by PL followed a Weibull kinetics, is exclusively photochemical and is an all-or-none process where the protein gets oxidized, decreases its alpha-helix content, unfolds and aggregates.