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

Abstract

For PPO-mediated proteolytic inhibition, pathways for both phaselic acid and chlorogenic acid may be good targets for engineering into alfalfa. Clovamide may be useful for inhibiting proteolysis without PPO.

Phenolic Profiles and Polyphenol Oxidase (PPO) Gene Expression of Red Clover (<i>Trifolium pratense</i>) Selected for Decreased Postharvest Browning

“…However, given the lack of change in PPO1 gene expression, the observed decrease in clovamide, which can bind to proteins in the presence or absence of PPO1 [9], may indicate that decreased browning has the greatest effect on concentrations of phenolics that can bind protein independently of PPO1 activity. Dependence on PPO4 activity cannot be ruled out because PPO4 can utilize clovamide as a substrate [10].…”

“…The decrease in p-coumaroyl malate over time ( Table 1) could be due to binding to proteins, because p-coumaroyl malate can inhibit proteolysis in alfalfa extracts, although the mechanism does not involve PPO or oxidation [9]. The observed decreases in isoflavones D, E, sissotrin, and total formononetin and biochanin A, may also indicate non-PPO-mediated binding to protein because formononetin and biochanin A lack an o-diphenol moiety, as do the majority of the red clover isoflavones [3].…”

“…PPO catalyzes the oxidation of compounds with an o-diphenol moiety to o-quinones, which then react non-enzymatically with amino acids to form brown protein-phenolic complexes [21]. Phaselic acid is a PPO substrate, while clovamide can bind to proteins in the presence or absence of PPO [8] [9].…”

Perennial peanut (Arachisglabrata Benth.) contains polyphenol oxidase (PPO) and PPO substrates that can reduce post‐harvest proteolysis

“…Red clover ( Trifolium pratense L.) was derived from a population of NewRC germplasm . Alfalfa ( Medicago sativa L.) plants expressing red clover PPO1 and control plants not expressing PPO1 were the segregating T1 progeny from a cross of a T0 PPO1 transgenic plant into a wild‐type background and have been previously described . Both red clover and alfalfa were grown in a greenhouse whose seasonal variation resulted in temperatures between 20 and 30 °C and light intensities between 400 and 1000 µmol m −2 s −1 .…”

“…The reduction in proteolysis is presumably by a mechanism that involves reaction of PPO‐generated o ‐quinones with nucleophilic amino acid residues present in endogenous plant proteases and/or proteolytic substrates. Unfortunately, it has been difficult to assess the true potential of the PPO/ o ‐diphenol system in animal nutrition experiments, but several studies suggest improved N use efficiency with diets incorporating PPO and o ‐diphenol‐containing red clover (see Sullivan and Zeller for a discussion of this).…”