ARS | Publication request: Determination of Polyphenol Oxidase Activity (Ppo) and Proteolytic Inhibition in Grasses

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: February 28, 2005
Publication Date: July 1, 2005
Publisher's URL: http://abstracts.aspb.org/pb2005/public/P56/8035.html
Citation: Marita, J.M., Hatfield, R.D., Brink, G.E. 2005. Determination of polyphenol oxidase activity (PPO) and proteolytic inhibition in grasses [abstract]. Plant Biology. p. 210.

Technical Abstract: Harvesting and storing high quality forage remains a challenge due to the potential high degree of protein degradation during ensiling. Red clover has high protein levels at harvest that are maintained during ensiling. Decreased proteolytic activity in red clover is due to polyphenol oxidase (PPO) activity and appropriate o-diphenol substrates. A project was undertaken to determine PPO activity in grass species and its potential role in proteolytic inhibition. Ten grass species were established in the greenhouse and in the field. The amount of PPO activity measured in each grass varied depending upon the species and upon the specific o-diphenol used as the primary PPO substrate. Orchardgrass, meadow fescue, ryegrass, and smooth bromegrass exhibited the highest PPO activities. Chlorogenic acid and caffeic acid were the preferred substrates, although there were differences among the most active grasses as to the levels of utilization. This suggests potential differences among the individual PPO enzymes. A browning assay associated with PPO activity, whereby the color change (i.e. browning) of a plant extract is monitored over time, has been an indicator of proteolytic inhibition. The browning reaction in grasses unlike red clover was not highly correlated with the loss of proteolytic activity. However, the addition of caffeic acid to buffered grass extracts resulted in proteolytic inhibition in grasses with substantial PPO activity. This indicates that several important grass species contain PPO activity, but lack the appropriate o-diphenol substrated to effectively inhibit proteolysis.