Enzymatic degradation of polar lipids in deep-frozen parsley.

Abstract

Under the frozen storage at usual storage temperatures of leafy tissues not pretreated by heat, enzymatic lipid degradation reactions take place, which lead already after a few weeks to a considerable or complete loss of the native polar lipids. These degradation processes being accompanied by a deterioration of the flavour have been studied in greater detail in parsley leaves. Among the reaction products we found large amounts of 6-acylmonogalactosyl diglycerides (formed from monogalactosyl diglycerides by enzymatic transacylation) and phosphatidic acid (formed from phospholipids through phospholipase-D action). The generally assumed reaction sequence: formation of free fatty acids by acyl hydrolases followed by hydroperoxidation through lipoxygenase and degradation of the hydroperoxidation through lipoxygenase and degradation of the hydroperoxides into off-flavour compounds may hence take place, if at all, only to a limited extent. Considerable phospholipase D as well as minor acyl transferase activities are detected at --24 degrees C, whereas at --32 degrees C the lipid loss is very low. Deterioration processes can be avoided by blanching, a treatment not leading to any substantial quality loss.