In vitro study of red clover polyphenol oxidase activity, activation, and effect on measured lipase activity and...

The goal of this paper was, first, to study the effect of red clover polyphenol oxidase (PPO) activity on protein-bound phenols and measured lipase activity in vitro and, second, to study the effect of PPO activation, measured as an increase in protein-bound phenols, as a result of degrees of damaging (not damaged, crushed, and freeze/thawed) of red clover before wilting on measured enzyme activity and in vitro lipid metabolism when incubated in a phosphate buffer. There was a positive relation between PPO activity and the occurrence of protein-bound phenols with a concomitant decrease in measured lipase activity, indicating a possibility to a direct inhibition of enzymes as a result of protein-bound phenols. Furthermore, damaging can activate PPO in red clover, measured as an increase in protein-bound phenols during wilting [0.7-20.6 nmol of tyrosine equiv (mg of protein)(-1)], again with a concomitant decrease in measured lipase activity [41.3-20.3 mumol of p-nitrophenyl butyrate (PNPB) min(-1) (mg of protein)(-1)]. Lipid metabolism during incubation of these forages in a phosphate buffer with ascorbic acid was only influenced by damaging when wilted for 24 h, with a lower lipolysis in crushed and freeze/thawed (52.9 and 32.6%, respectively, after 8 h of incubation) material compared to all other treatments (on average 60.4% after 8 h of incubation).