Effect Of Phenolic Acids On Fermentation Of Cell Walls From Crop Residues By Rumen Microorganisms

Six experiments were conducted to determine the content of alkali-labile phenolic monomers present in crop residues and different position of corn stover, the effect of kinds and concentrations of phenolic acids on rumen microbial fermentation, and the dynamic of phenolic acids during the fermentation in vitro.In Expt. 1, the composition and the proportion of alkali-labile phenolic monomers were determined by HPLC after alkaline hydrolysis in corn stover, rice straw and wheat straw. In corn stover, p-coumaric acid (t-PCA), ferulic acid( t-FA ), vanillic acid (VA), protocatechuic acid (PRA), sinapic acid (t-SA ), syringic acid (SYA), caffeic acid (CA), p-hydroxybenzoic acid (PHBA), and gallic acid (GA) were detected. In rice straw and wheat straw, however, PRA, PHBA and CA weren not yet detected. The total content of alkali-labile phenolic acids was most abundant in corn stover (1.23%), followed by rice straw (1.21%) and the wheat straw (0.87%), with. t-PCA and t-FA as predominant phenolic acids. Based on the in vitro digestion data, the content of both total phenolic acids and PCA or FA did not show any clear relation to the dry matter digestibility (DMD).In Expt. 2, the kind and concentration of alkali-labile phenolic monomer were determined in stems, leaves (including leaf sheath) and husks from typical and high-oil corn plants. The concentration of total alkali-labile phenolic acids and most phenolic acids in stems, leaves and husks from typical corn plants were higher than those from high-oil corn plants. t-PCA and t-FA were still the most abundant phenolic acids in every positions of the corn plants. Except the leaves from typical corn plants, CA was not detected in other positions of both kinds of corn plants. The unclear relation between phenolic acids and DMD was also found in this experiment. Because of higher hemicellulose content of husks, the gas production and DMD were higher in the position of husks than stems and leaves.In Expt. 3, nine phenolic acids were used to investigate the effect of phenolic acids on ruminal fermentation of fibrous materils using batch culture in vitro. Addition of phenolic acids at 60 mg/g of mixed fibrous diets did no show any effect on rumen fermentation traits, except the addition of SYA had a tendency of increased rate of gas production (p<0.05). When each of phenolic acids was used as a sole fermentation substrate, the gas was produced in vitro, suggesting an ability to degrade phenolic acids by ruminal microorganisms. Among 9 phenolc acids used, SYA produced the most amount of gas, whereas PCA produced the least amount, indicating that there was a difference in utilization of phenolc acids by rumen microorganism.In Expt. 4, the effect of various contents of three kinds of phenolic acids on in vitro rumen fermentation was tested in batch culture in vitro. The result showed that PCA added at any content altered the dynamics of gas production, rumen fermentation traits, and fermentation pattern to a certain extent. PCA added at 90 mg/g could markedly inhibit the fermentation. In comparison with PCA, FA had less inhibiting effect on rumen fermentation in terms of gas production, rumen pH, ammonia and VFA concentration. Although PHBA had a significant (P<0.001) effect on the dynamics of gas production, ammonia concentration, and VFA production, the fermentation pattern was little changed,suggesting less inhibition effect of rumen fermentation due to PHBA.In Expt. 5, the composition and the proportion of alkali-labile phenolic monomers in the blank rumen fluid and both substrate-based rumen fluid and pellets were determined by HPLC. Although highest contents of t-PCA and t-FA were present in corn stems, the content of PRA was highest in the blank rumen fluid, and the content of t-PCA and t-FA were only in the intermediate place, being about 0.20u.g/ml rumen fluid. Therefore, no exact relationship was found between the content of phenolic acids in the plant substrate and in rumen fluid. The reason for high and more fluctuated apparent digestibilities of most phenolic monomers was...