Transformations of structural phenylpropanoids during cell wall digestion

Abstract

Phenylpropanoids limit the degradation of cell wails of roughages in herbivores but at the same time undergo transformations in the digestive tract. This review outlines the main transformations that occur in the rumen. All the monomeric aromatics tested are fully degraded under anaerobis conditions which favour electron transfer. Six main strains of bacteria degrade monomeric phenols in the rumen by several mechanisms. In addition, some fungi and bacteria are able to release, and possibly to metabolise the esterified hydroxycinnamic acids found in forage cell walls. The first step in the degradation of these acids is their reduction to non-toxic compounds, which are often growth factors. However, total degradation of monoaromatics is diicult to achieve in vivo because of the small population of organisms able to metabolise them and the limited transit time of the substrates in the rumen. Oligolignols are also degraded to different extents depending on their size and molecular structure. Lignins are partly solubihsed during cell wall degradation. They may also undergo other transformations such as demethylation and dehydroxylation. The amount of lignin that seems to be degraded in rumen fluid is low but probably higher than under other anaerobic environments over the same period of time. It is generally accepted that the digestibility of forage lignins is low. However, the wide range of values measured (from minus 0.46 to 0.64) is related either to the measurement method or to the transformations that the lignins may undergo in the digestive tract, or to both. An indigestible fraction of lignins could serve as a reliable cell wall marker but none of the fractions used to date has proved entirely satisfactory for this purpose. Future research in this field would involve better knowledge about the transformation of phenylpropanoids and the development of microbial activity on these compounds. This would improve phenol& degradation and consequently carbohydrate utilization.

Effect of lignin linkages with other plant cell wall components on in vitro and in vivo neutral detergent fiber digestibility and rate of digestion of grass forages

“…Consistent differences were found among all 3 diets between intake and excretion of the phenolic acids, with ranges between 10 and 42 g and 4 and 38 g for TMR and NDF samples, respectively. The amount of FA (<0.50 g of total FA per cow) in urine represented only a small portion of the phenolic acid ingested, and therefore a portion of it must be digested as indicated by Besle et al (1995). Ferulic acid is more extensively degraded than pCA both in vivo (Giger, 1985) and in vitro, where it is metabolized at the same rate as hemicellulose (Jung, 1989).…”

Fontes de amido e proteína para vacas leiteiras em dietas à base de capim elefante

“…al, 1982). A digestibilidade aparente no rúmen e trato digestivo total foi determinada através da utilização de lignina como marcador interno de indigestibilidade (Besle et al, 1995).…”

Uso de reatores biológicos com fungos para remoção de fenol de água residuária sintética

“…Sob condições aeróbias, a presença de oxigênio no meio é necessária para preparar o fenol para a fissão do anel, usando enzimas para catalisar a incorporação de um ou dois átomos de oxigênio para formar ortho -catecol ou para -catecol, compostos dihidróxi e, como resultado do metabolismo, são formados ácidos (BESLE et al, 1995 (COSTA et al, 2004).…”