Oxidation of ortho‐diphenols in red clover with and without polyphenol oxidase (PPO) activity and their role in PPO activation and inactivation

Abstract

Oxidation of phenol to quinone with its subsequent binding and complexing with protein in red clover (Trifolium pratense L.) when fed to ruminant livestock has been shown to improve nitrogen‐use efficiency and the deposition of polyunsaturated fats into animal products. This oxidation has, almost exclusively, been attributed to the activity of the enzyme group polyphenol oxidases (PPOs) and, specifically, catecholase during conservation. However, during conservation, temporal inactivation of PPO occurs and oxidation of phenolic substrate may occur through other mechanisms not associated with PPO. T1 progeny of a cross between a red clover clone having normal levels of foliar PPO activity and a transgenic PPO‐silenced red clover plant with undetectable levels of PPO activity were divided into two populations based on the presence of the silencing transgene and lack of measurable PPO activity (PPO−) or the absence of the silencing transgene and normal levels of PPO activity (PPO+). This material was subsequently used to determine the relevant extent of phenolic oxidation in the presence and absence of PPO activity under two damage regimes (heavy and light). PPO+ and PPO− material was passed through a garden shredder as the light‐damaged regime, or frozen at −20°C as the heavy damaged regime. Material was left at room temperature and sampled at regular intervals for the determination of PPO enzyme activity (active and total), PPO activation (conversion from latent to active forms) and formation of protein‐bound phenol (PBP) as a measure of oxidation. Experiments with red clover leaf extracts were carried out to determine the mechanism for the temporal activation and inactivation (loss of enzymatic activity) of PPO during wilting. PBP formation was evident in both PPO− and PPO+ treatments with the response further catalysed during the first 2 h by extent of damage that increased the activation of PPO, but which also resulted in a more rapid temporal inactivation of PPO. PBP formation, PPO activation and PPO inactivation were all shown to be mediated predominantly by quinone binding. A role of non‐PPO oxidation in PBP formation in wilted red clover is reported, showing the importance of o‐diphenolic substrate concentration and not just PPO activity to increase nitrogen use efficiency and the deposition of polyunsaturated fats into animal products.

Efficacy of various naturally occurring caffeic acid derivatives in preventing post‐harvest protein losses in forages

“…Further, in the case of clovamide, incubation of 3 mmol g −1 soluble protein ( o ‐diphenol basis) with control alfalfa extract with oxygen levels reduced by replacing the reaction headspace with N 2 resulted in a substantial reduction in observed browning and a significant increase in relative amino acid release (0.64 ± 0.050 versus 0.51 ± 0.008 for N 2 ‐ and non‐treated reactions, respectively, P < 0.05 (directional hypothesis)), indicating at least part of the effect is due to oxidation of clovamide. This result is consistent with a recent report that substantial protein‐bound phenol is generated upon tissue damage even in red clover lacking measurable PPO activity . More effective purging of O 2 from the reaction prior to incubation might result in an even more dramatic increase in proteolysis in the presence of clovamide.…”

The effect of high polyphenol oxidase grass silage on metabolism of polyunsaturated fatty acids and nitrogen across the rumen of beef steers1

“…Polyphenol oxidase activity in all silages was low due to rapid deactivation of PPO by quinone binding formed through the PPO-catalyzed conversion of diphenol substrate as a negative feedback of PPO activity . Lee et al (2013) reported a rapid decline in PPO activity in macerated red clover within 1 h, with the rate relating to the extent of damage of the crop. Deactivation would continue to occur whilst a-c Means within row not bearing a common letter differ (P < 0.05).…”

Dynamic role of single‐celled fungi in ruminal microbial ecology and activities

“…However, (Zhang et al () reported that inclusion of S. cerevisiae lowered faecal LPS and plasma LPS which could indicate endotoxin absorption from/or production in the rumen was low. In beef cows, Lee et al () reported that dietary yeast wall supplements can effectively decrease the concentration of free LPS in plasma, digesta and faeces. The absorption of endotoxin puts enormous pressure on the liver for detoxification, and in extremes cases, they instigate the uptake of mycotoxin; such as trichothecenes and fumonisins that elicit inflammatory and immunosuppressive responses (Jenkins ).…”