Effect of various post-harvest treatments on the green color and chlorophyll retention of southern peas, Vigna sinensis

Tennessee processors of frozen Southern peas have observed a rapid loss of green color in the post harvested raw product. Color is one of the most important quality factors in grading peas by USDA standards. Therefore, a loss of greenness may result in a lower grade for the frozen product. This study was initiated in order to gain more information on the factors which may be responsible for this loss of green color.

Southern peas (Vigna sinensis, Mississippi Silver var.) were harvested in the mature green stage, shelled and stored at three temperatures (40°, 75°, 90° F) for three time periods (8, 16, 24 hrs.). The effects of illumination and water storage were also incorporated in this experiment. A second experiment investigated the effects of storage under vacuum, nitrogen, air and storage in the pod.

The effect of these treatments was measured by spectrophotometric analysis of chlorophyll extracts, C.I.E. conversion of Color Eye Colorimeter values, color panel evaluation, pH values, and enzymatic activity.

The data indicated that an increase in time and temperature caused an increased conversion of chlorophyll to pheophytin. Water storage and illumination had no significant effect on chlorophyll retention. Unshelled peas stored at 40° F retained more chlorophyll than all other treatments. The enzymatic activity of peroxidase and lipoxidase was significantly affected by treatments, but was not correlated with chlorophyll retention or color measurements.