ENZYME ACTION AND OFF‐FLAVOR IN FROZEN PEAS^a

Abstract

Enzymes are believed to be responsible for the development of off-flavor in raw and underblanched vegetables during frozen storage (1). A variety of enzymes have been suggested as being causative agents in flavor deterioration (l), but interest has centered mainly around catalase and peroxidase. Tests for the presence of these two enzymes have long been used as criteria of adequacy of blanching of vegetables prior to freezing. Furthermore, a reasonably good correlation has been observed between the presence of residual amounts of these enzymes and extent of off-flavor in frozen vegetables. To date, however, the identity of the responsible enzymes has remained obscure.Recently it has been shown that lipoxidase and lipase are responsible for the progressive deterioration of lipids in raw peas during frozen storage (5, 12). These changes in the lipids, characterized by increases in titratable acidity, development of lipid peroxides, and loss of chlorophyll, closely paralleled the progressive development of off-flavor (7). It was deemed most likely that lipoxidase and possibly lipase are primary causative agents in the production of off-flavors during frozen storage of raw peas.Proof of involvement in off-flavor development of any or all of the above enzymes may be ascertained by a study of their action in model systems. Preparations of catalase, peroxidase, lipoxidase, and lipase of known specific activity were added to enzymatically inert blanched peas, and the samples analyzed after a suitable period of frozen storage. This paper reports the production of off-flavors during the frozen storage of macerates of blanched peas, brought about by the addition of enzymes, and a correlated chemical study of lipid deterioration. MATERIALS AND METHODSPerfected Freezer peas, grown on Experiment Station plots, were harvested and processed as described earlier (5) and stored in 30-pound tins at -17.8" C. The blanched peas to which enzymes were to be added were thawed and blended for 2 minutes in a five-quart Waring blender with one-half their weight of water. The resultant pea slurry was divided into 100 g. lots, and the various enzyme preparations were added and well mixed by stirring. The amounts of enzymes added to blanched peas were calculated to be twice the amounts present in fresh raw peas. Four series of samples were prepared in which the 4 enzymes were added singly and in all possible combinations. Samples of blanched pea slurry with no added enzymes were included as controls in each series. Two series were used for taste test evaluation for flavor and color (I,?), and two series were used for chemical analysis. Samples were placed in cellophane bags inside waxed cartons, frozen, and held in storage at -17.8" C.Catalase activity was measured manometrically by the Thompson method ( I r ) . Crystalline catalase (General Biochemicals, Inc., Chagrin Falls, Ohio), specific activity -0.018 mg. produced 2.5 ml. 0 2 , was added at the level of 17 mg. per 100 g. lot of peas.One gram of the resultant mixture produced 2.8 ml. of ...

Effect of Blanching on Enzyme Activity and Quality Changes in Green Peas

“…LIP has been implicated in loss of chlorophyll and production of off-flavors in frozen green peas (Wagenknecht and Lee, 1958). However, results have not been presented detailing the activity of the enzyme under varying blanch conditions and subsequent frozen storage.…”

Peroxidase and Lipoxygenase Influence on Stability of Polyunsaturated Fatty Acids in Sweet Corn (Zea mays L.) during Frozen Storage

“…However, some studies have shown that POD is not directly involved in quality deterioration of frozen unblanched vegetables and its complete inactivation may result in overblanching (Williams et al, 1986). The measure of LOX activity has been suggested as an indicator of adequacy of blanching for several vegetables (Axelrod et al, 1981;Sheu and Chen, 1991;Chen and Hwang, 1988;Williams et al, 1986;Chen and Whitaker, 1986;Wagenknecht and Lee, 1958) including sweet corn (Garrote et al, 1985;Wagenknecht, 1959). It is closely related to destruction of essential fatty acids, off-flavor development and pigment degradation.…”

Changes in Peroxidase Activity, Hexanal, Ascorbic Acid and Free Sulfhydryl in Blanched Asparagus During Frozen Storage

“…IT HAS BEEN well documented that holding plant tissue at -'2O"C retards but does not totally prevent quality changes and that these changes are associated with enzymatic action (Joslyn, 1949;Lee et al, 1955;Wagenknecht and Lee, 1958;Pinsent, 1962). Several factors affect the rate of enzyme inactivation during heating (Aylward and Haisman, 1969).…”