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RESEARCH PRODUCT

Effects of tannin-containing diets on small ruminant meat quality

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description

Tannins are phenolic compounds present in several forages, tree leaves and by-products used for small ruminant feeding in the Mediterranean area. Although the effects of dietary tannins on small ruminant growth performances have been largely studied, only in the last ten years researchers have started to study the effects of tannins on meat quality. Meat from small ruminants given tanniniferous diets is lighter in colour compared to meat from animals given the same diets but in which the effects of tannins have been eliminated by the supplementation of polyethylene glycol. This result has been obtained with tannins from different feeds (carob pulp, acacia leaves or sulla fresh herbage). Recent in vitro studies seem to indicate that a possible effect of tannins on meat colour could be due to a reduced microbial biosynthesis of vitamin B12 which is a precursor for the synthesis of haeme pigments. Meat from lambs given carob contains less conjugated linoleic acid compared to meat from animals fed the same diet but supplemented with polyethylene glycol. A possible explanation of this result has been proposed recently after an in vitro experiment on linoleic acid isomerase; it has been shown that when cattle ruminal fluid is incubated with tannins exctracted from acacia, carob or quebracho, the conjugated linoleic acid formed from linoleic acid was lower compared to the mount of conjugated linoleic acid produced in tannin-free rumen fluid. Also, the ruminal biosynthesis of odour-active compounds seems to be affected by tanniniferous diets. This is the case of skatole (3-methylindole) and indole which confer unpleasant flavour connotations to lamb meat.