Variation of Tannin Contents in Selected Agro-Industrial Byproducts and their Biological Activity in Precipitating Protein

Agro-industrial by-products containing tannins have potential to be used as alternative ruminant feed sources. To explore the functional effects of agro-industrial by-products on livestock production, the contents of tannins such as total extractable phenolics (TEPH) and condensed tannins (CT), in 15 kinds of by-products were determined and their protein-precipitating capacity (PPC) was also measured. TEPH content was the highest in chestnut husk, followed by tea grounds. Grape skin, winery residue and chestnut husk showed high CT content. Furthermore, TEPH, but not CT, content was positively correlated with PPC (p<0.001). The PPC on a TEPH basis was the highest in black tea grounds, followed by cedar bark and cypress bark. Green tea grounds, banana peel, grape skin, and winery residue showed moderate PPC, whereas citrus peels and coffee grounds did not show any PPC. Among these by-products, four by-products showing moderate PPC might have potentiality to be considered as feedstuffs that protect protein degradation in the rumen; particularly green tea grounds would be preferred as protein supplements due to high CP content and moderate PPC.