Tannin specific activity

The tannin specific activity (TSA) of phenolic extracts and beverages can be directly determined from different sample flows without previous dilutions or any other treatment. 

Converse results were found in vivo in the rumen of lambs fed a basal diet (barley grains-based concentrate) with or without the supplementation of quebracho tannins (Vasta et al. 2010). In this study, the LA-I specific activity was lower for the tannins-receiving lambs while the concentration of total CLAs produced in the assay was not affected by tannins supplementation. In the same smdy, RA accumulated in the rumen of the tannins-fed lambs, while it was absent in the rumen content of the lambs not supplemented with tannins (Fig. 9.2), snggesting that tannins hampered the conversion of RA to VA. 

There are few, if any, specific inhibitors of lipase activity. Instead, reported inhibition of lipase by saponins (Han et al., 2002), polysaccharides and tannins (Longstaff and McNab, 1991) is probably due to the non-specific interactions these phytochemicals have with proteins. 

TMS production involves one specific functional group (-OH, -COOH, =NH, -NH2, or -SH), which loses an activated hydrogen and is replaced by a trimethylsilyl group (Proestos et ah, 2006). To achieve silylation, some authors have used BSTFA (N,0-hA(trimethyl-silyl)trifluoroacetamide) and TMCS (trimethylchlorosilane) successfully in several matrices (e.g. aromatic plants, cranberry fixiit) (Zuo et ah, 2002 Proestos et ah, 2006). Using silylated derivatives is advantageous for several reasons phenols and carboxylic acids are prone to silylation, these compounds can be derivatized in the same part of the process, and the minor products do not impede analysis and are well documented (Little, 1999 Stalikas, 2008). A two-step methylation procedure was used to analyze catechins and tannins in plant extracts. The first step used trimethylsilyl diazomethane (TMS-diazomethane) to pre-methylate the sample, and the second step used thermally assisted hydrolysis and methylation (THM). The pre-methylation step with TMS-diazomethane stabilized the dimer molecule m/z 540) by minimizing isomerization and reducing reactivity. (Shadkami et ah, 2009). 

However, not all related species or conspecific populations respond similarly under the same UV influence. For example, Betula pendula and B. resinifera, two closely related birch species collected from populations in Europe and Alaska, generally produce a number of flavonoids, hydroxycinnamic acids, and condensed tannins in larger quantity in exposed leaves to artificial UV-B photon fluxes (4.9 kJ m d for 3 hr/day of biologically active radiation) than in non radiated plants (Lavola, 1997). In B. pendula populations the major increase was in flavonoid synthesis but in B. resinifera the bias was towards the hydroxycinnamic acids and condensed tannins. Besides, allopatric (geographically distant) populations of birch reacted differently in the synthesis of specific compounds. For example, chlorogenic acid increased by 22 and 92% in plants from Germany and Alaska, respectively, but in Finnish plants there was no increment at all. 

Almond emulsin is prepared from defatted crushed almonds by extraction with water and precipitation of the extracts with alcohol. The dried powder is known as almond emulsin. A preparation of considerably more activity is obtained by treatment of the almond meal with zinc sulfate solution and precipitation of the enzymes from solution by the addition of tannin. The tannin is separated from the enzyme by extraction of the precipitate with acetone, and the solid residue is the Rohferment of Helferich 23) which has been used for many of the studies of the specificities of the enzyme components of almond emulsin. The Rohferment usually has a /S-gluco-sidase value of about 1. 

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