Hydroperoxide can also be formed via an alternate route in which the reaction of
polyunsaturated lipid with oxygen is catalyzed by the enzyme lipoxygenase. It specifically
oxidizes polyethenoid acids containing methylene-interrupted double bonds that are in the cis
configuration such as those in linoleic, linolenic, and arachidonic acids but not in oleic acid.
Free-radical intermediates occur during lipoxygenase catalysis, and these can lead to
cooxidation of easily oxidized compounds such as carotenoids and polyphenols.
Lipoxygenase are present in spices, wheat flour, and vegetables and will catalyze the
oxidation of unsaturated fats in dried and drying produce, increasing the rate at which
peroxides and volatile breakdown products are generated.