Investigating carotenoid loss after drying and storage of

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7. Involvement of enzymes
carotene by soybean lipoxygenase and linoleic acid, and autoxidation of !-carotene by
linoleic acid and soybean lipoxygenase similarly demonstrated that autoxidation was
significant and !-carotene degradation was accelerated with addition of lipoxygenase at
pH 8 (about five times the rate of autoxidation). In the present study, lipoxygenase
degradation rate was 0.020 min -1 at pH 6.0 and 0.035 min -1 at pH 7.4. A faster !-
carotene degradation rate at higher pH compared to lower pH resulted of more optimal
lipoxygenase activity at alkaline pH. In contrast, autoxidation (with linoleic acid) was
not influenced by pH (at pH 6; in presence or absence of H2O2: 0.016 and 0.016 min -1
respectively and; at pH 7.4: 0.017 and 0.015 min -1 respectively). Addition of peroxidase
or with H2O2 resulted in slower oxidation of !-carotene compared to autoxidation in
presence of linoleic acid at pH 7.4 (0.008; 0.009 and 0.015 min -1 respectively). This
further highlights the importance of autoxidation rate of !-carotene that can be
comparable with enzymatic oxidation under some conditions.
Filtered extract from sweet potato flour was not significantly different from the control
in terms of rate constant (k) (ANOVA; p