Resumen de Hydrogen bonds in the binding of some polyphenols from Quebracho (Schinopsis spp.) to soybean meal protein under in vitro ruminal conditions
C. Velasquez, M. Suárez, Martha L. Pabón, Juan Evangelista Carulla Fornaguera
The extent of binding to soya protein of a commercial tannin (Quebracho), its ethyl acetate extract, the major putative compound (fisetinidol-(4,8)-cathequin-(6,4)-fisetinidol), and the acetylated and methylated derivatives of the major latter was evaluated incubating them with soybean meal under in vitro ruminal conditions for 48h. The protein binding activity was estimated measuring changes in ammonia concentration when the tannin was incubated with soybean meal at a proportion of 8% of the dry weight. As compared to soybean meal alone (control), ammonia concentration decreased by 19, 27, and 31% for quebracho, the ethyl acetate extract of quebracho and the major compound, respectively, indicating concentration of the protein binding activity. Acetylation or methylation of the major compound resulted in corresponding decreases in the concentration of ammonia by 21 and 6%. This suggested that as the possibility of hydrogen bond formation decreases (being less with methylation than with acetylation), the binding to the protein is reduced but is not eliminated completely. Therefore, our hypothesis is that the main interactions between fisetinidol-(4,8)-cathequin-(6,4)-fisetinidol and soybean protein in an in vitro ruminal system are hydrogen bonds and that only a few hydrophobic interactions are present.
