Screening legume forages for soluble phenols, polyphenol oxidase and extract browning†

Red clover (Trifolium pratense) is a legume that will brown quickly upon harvesting. This browning of red clover has been correlated to a reduction in proteolysis and requires the presence of a polyphenol oxidase and soluble phenol substrates. A method was developed to screen forages for soluble phenols, soluble polyphenol oxidase activity and extract browning. Fourteen different legumes and 24 red clovers (22 plant introductions and two cultivars), field grown in replicated plots, were screened. Of the different legumes, only red clover had measurable soluble polyphenol oxidase activity (7.70 abs g -1 leaf) and underwent browning (0.245 abs g -1 leaf). This extract browning and polyphenol oxidase activity were present in all red clovers tested and ranged from 0.153 to 0.458 and 6.00 to 9.00 abs g -1 leaf, respectively. All of the legumes, including all red clovers, gave a positive response for soluble phenols