Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2004
Publication Date: 8/11/2004
Citation: Cheng, M., Mcphee, K.E., Baik, B. 2004. Bleaching of green peas and changes in enzyme activities of seeds under simulated climatic conditions. Journal of Food Science. 69(7):511-518. Interpretive Summary: Field produced green pea seed is prone to lose chlorophyll and overall green color in the later stages of maturity in the presence of intense sunlight and moisture. Significant loss of green color reduces quality and results in devaluation of the harvested crop. Chlorophyllase, lipoxygenase and chlorophyll degrading enzyme were studied to determine the underlying enzymatic pathway responsible for color loss in maturing pea seed. Chlorphyllase showed the strongest relationship with chlorophyll degradation and loss of green color while lipoxygenase and chlorophyll degrading peroxidase showed no relationship. Additionally, it was shown that loss of green color requires both the presence of moisture and light. Light alone did not result in signficant color loss. Reduced production of chlorophyllase during seed maturation may result in improved color retention and maintenance of high quality seed.
Technical Abstract: The effects of simulated climatic conditions on green color loss of peas (Pisum sativum) and related enzyme activities were investigated. Seeds of two green pea cultivars showing different resistance to green color bleaching were subjected to light only, soaking in water without light and soaking in water with light. Green color and chlorophyll loss were highest in seeds soaked in water and exposed to light, less in seeds soaked in water under dark conditions and least in seeds exposed to light only. Increased chlorophyllase activity was associated with loss of green color and chlorophyll, while no significant relationship was found between chlorophyll loss and lipoxygenase or chlorophyll degrading peroxidase activity. Susceptible and resistant cultivars had significant differences in green color, chlorophyll content, chlorophyll a/b ratio and chlorophyll degradation kinetics constant when seeds were soaked in water and exposed to light. Enzyme activity was not significantly different between the two cultivars. Soaking led to more green color loss, chlorophyll breakdown and chlorophyllase activity than light exposure. Chlorophyllase may be the key enzyme responsible for green pea bleaching instead of the oxidative chlorophyll degradation pathway with lipoxygenase or chlorophyll degrading peroxidase