Abstract
Tannic acid (TA) is a polyphenolic compound with a health-promoting potential for humans. It is hypothesised that TA effects on the relative weight of internal organs and biochemical blood indices are modified by dietary protein level in rats. The study involved 72 rats divided into 12 groups fed diets with 10 or 18% of crude protein (CP) and supplemented with 0, 0.25, 0.5, 1, 1.5 or 2% of TA. After 3 weeks of feeding, the relative weight of the caecum was greater in rats fed TA diets, while feeding diets with 10% of CP increased the relative weight of the stomach, small intestine and caecum, but decreased that of kidneys and spleen. Albumin concentration was higher in rats fed 0.25% and 0.5% TA diets than in rats given the 2% TA diets. The 2% TA diets reduced creatine kinase (CK) activity compared to non-supplemented diets and those with 0.5, 1 and 1.5% of TA. Rats fed the 10% CP diets had a higher activity of alkaline phosphatase, amylase, and γ-glutamyltransferase as well as the concentration of iron and cholesterol, but lower that of urea and uric acid. The interaction affected only cholinesterase activity. In conclusion, TA induced caecal hypertrophy and could act as a cardioprotective agent, as demonstrated by reduced CK activity, but these effects were not modified by dietary protein level.
Highlights
Tannic acid (TA) is a polyphenolic compound consisting of a central glucose molecule, which hydroxyl groups are linked by ester bonds with gallic acid moieties
All TA diets significantly increased (P < 0.05) the relative weight of caecal tissue compared to non-supplemented diets
The present study demonstrated a hypertrophic effect of higher crude protein (CP) level on kidneys, which could be explained by the metabolism of larger quantity of nitrogenous compounds in these organs
Summary
Tannic acid (TA) is a polyphenolic compound consisting of a central glucose molecule, which hydroxyl groups are linked by ester bonds with gallic acid moieties. One molecule contains 8 to 10 moles of gallic acid per mole of glucose [1]. TA is a well-known representative of gallotannins, a class of hydrolysable tannins, which are widely distributed throughout the feeds and foods of plant origin [2]. TA is a potent antioxidant with antimutagenic and anticarcinogenic properties. It may protect DNA against oxidative damage and may be useful in the therapy of diseases related to oxidative stress such as colorectal cancer and heart and liver damage [3,4,5]. Its health-promoting potential may be applied in farm animal nutrition, as previously shown for gallotannin preparation that improved feed efficiency and reduced proteolytic fermentation in the caecum of piglets [6].
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