Octanol−Water Partition Coefficients for Predicting the Effects of Tannins in Ruminant Nutrition

Abstract

Tannins can cause beneficial or harmful nutritional effects, but their great diversity has until now prevented a rational distinction between tannin structures and their nutritional responses. An attempt has been made to study this problem by examining the octanol-water solubilities of tannins. A relatively simple HPLC method has been developed for screening mixtures of plant tannins for their octanol-water partition coefficients (Kow coefficients). Tannins were isolated from the fruits and leaves of different Acacia, Calliandra, Dichrostachys, and Piliostigma species, which are known to produce beneficial or harmful effects. The Kow coefficients of these tannins ranged from 0.061 to 13.9, average coefficients of variation were 9.2% and recoveries were 107%. Acacia nilotica fruits and leaves had the highest Kow coefficients, that is, 2.0 and 13.9, respectively. These A. nilotica products also have high concentrations of tannins. The combined effects of high octanol solubilities and high tannin concentrations may explain their negative effects on animal nutrition and health. It is known that compounds with high octanol solubilities are more easily absorbed into tissues, and it is, therefore, proposed that such compounds are more likely to cause toxicity problems especially if consumed in large quantities. According to the literature, tannins in human foods tend to have low Kow coefficients, and this was confirmed for the tannins in Piliostigma thonningii fruits. Therefore, unconventional feeds or browse products should be screened not only for their tannin concentrations but also for low octanol-water partition coefficients in order to identify nutritionally safe feeds and to avoid potentially toxic feeds.

Antihypertensive Effect of Boysenberry Seed Polyphenols on Spontaneously Hypertensive Rats and Identification of Orally Absorbable Proanthocyanidins with Vasorelaxant Activity

“…Measurement of log P ow of the main polyphenolic components revealed that PAs (log P ow from À1:00 to 0.10) were slightly more hydrophobic than the dimeric and trimeric ETs (log P ow from less than À3:0 to À2:0). Values for EC, 0.26 in the polyphenol fraction and 0.33 for the reference compound, were coincident with those reported by MuellerHarvey et al 21) As different polyphenolic profiles are extracted depending on the polarity of the extracting solvent, 25) a water-solvent biphasic partition system using several solvents with intermediate polarities (dielectric constants from 0 to 1) was examined for the separation of PAs and ETs. Respective partition between water and ethyl acetate (dielectric constant of 0.73) successfully yielded an ET fraction with no PAs and a PA fraction containing PAs (8.88%).…”

“…Octanol-water partitioning was carried out in a manner similar to the method of Mueller-Harvey et al 21) Aliquots of a polyphenol fraction from boysenberry seeds were added to a mixture of octanol and water. The octanol and water phases were separated after vigorously stirring for 30 min.…”

Inhibition of α-amylase activity by condensed tannins

“…The interaction of procyanidins with proteins has been studied using several technical approaches (Baxter, Lilley, Haslam, & Williamson, 1997;Hagerman & Butler, 1981;Mueller-Harvey et al, 2007;Papadopoulou, Green, & Frazier, 2005). Present knowledge indicates that this interaction is affected by parameters of the protein (molecular size, hydrophobicity, structural flexibility), the polyphenol (degree of polymerisation, extent of galloylation, structural flexibility), and the environment (temperature, pH, ionic strength, presence of organic solvents and presence of carbohydrates) (Carvalho, Póvoas, Mateus, & de Freitas, 2006).…”

Kinetics and binding capacity of six soils for structurally defined hydrolyzable and condensed tannins and related phenols

“…This confirms that sorption capacity is similar for polyphenols with similar polarities, across a wide range of smaller polyphenols and tannins including compounds from both major classes of tannins. It is important to note that the reported K ow values for tannins range from 10 -4 to 10 3 (Mueller-Harvey et al 2007). Given the importance of polarity in dictating sorption of tannins, and the wide range of polarities reported for polyphenols, it is clear that tannins cannot be considered as a single class of compounds with common sorption characteristics.…”

“…Procedures for extracting compounds from soils typically employ a single solvent in which polyphenols are generally soluble, such as methanol (Muscolo and Sidari 2006;Kuiters and Denneman 1987;Cecchi et al 2004). Given the wide range of polarities of natural polyphenols (Frazier et al 2010;Mueller-Harvey et al 2007) and the importance of polarity in determining sorption to soil (see Table 1), we developed a novel extraction procedure that uses a series of solvents with differing polarities. We validated the method using soils amended with known amounts of defined polyphenols.…”