Investigating carotenoid loss after drying and storage of

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7. Involvement of enzymes
Soybean lipoxygenase activity was lower at pH value of 6.0 than 7.4 (0.013 against
0.141 mmol conjugated diene.min -1 .mol -1 ). Hence, in presence of linoleic acid and at pH
6.0, horseradish peroxidase was more efficient to bleach !-carotene than soybean
lipoxygenase (0.037 against 0.020 min -1 respectively) but it was the opposite at pH value
7.4 (0.022 against 0.035 min -1 respectively). To our knowledge this is the first time that
horseradish peroxidase was compared to soybean lipoxygenase for !-carotene oxidation
rate in a buffer medium. This highlights the strong link existing between enzymatic
activity due to pH variation and oxidation rate of !-carotene. Lipoxygenase has been
demonstrated to be an efficient oxidative agent of !-carotene (Wache et al. 2003). This
result further shows that peroxidase could be as equally efficient as !-carotene oxidative
agent.
An interesting observation is that addition of H2O2, which is peroxidase’s most usual
substrate, did not significantly increase the cleavage activity compared to the simple
enzyme both at pH 6.0 and 7.4 (ANOVA; p