[Enzymatic oxidation reaction in frozen parsley].

During frozen storage of (non-blanched) parsley, substances are formed showing absorption (234 nm) typical for hydroperoxidienoic acids with conjugated double bonds. However, only small quantities of these compounds are found in the frozen material as compared to other lipid degradation products; for instance, during 2 months at -18 degrees C only 0.1% of the fatty acids (bound to polar lipids) present in fresh parsley are transformed into dienoic acids. These low dienoic acid concentration are nevertheless sufficient to explain off-flavour formation since the sensory threshold values of the degradation products are in the range of some ppb only. After storage for 2 months at -24 degrees C no hydroperoxidienoic acids were found which means that this temperature, in contrast to the usual storage temperature of -18 degrees C, provides practically full protection against lipoxygenase-catalyzed spoiling reactions.