Nutritive value and polyphenol content of pomegranate seed pulp ensiled with different tannin-inactivating agents

• Tannin-inactivating agents altered polyphenols of pomegranate seed pulp (PSP).
• Calcium hydroxide and urea reduced total phenols and total tannins of PSP.
• Urea did not reduce punicalagin A and Ellagic acid (potent antioxidants) of PSP.
• Urea appeared to be the most suitable agent for ensiling of PSP.

This study was conducted to investigate the effect of addition of polyethylene glycol (PEG), urea, and calcium hydroxide as tannin-inactivating agents, on the chemical composition, polyphenolic compounds content, and rumen degradability of ensiled pomegranate seed pulp (PSP). The experimental treatments were as: (1) PSP ensiled without additive, (2) PSP ensiled with PEG, (3) PSP ensiled with urea, and (4) PSP ensiled with calcium hydroxide. The results indicated that urea and calcium hydroxide addition reduced (P < 0.001) the total polyphenolic compounds (TP) and total tannin (TT) contents of PSP, whereas the condensed tannin (CT) content was not affected by the additives. The hydrolyzable tannin (HT) content of PSP was reduced (P < 0.05) with calcium hydroxide addition, and the levels of punicalagin A and ellagic acid (EA), which are potent antioxidants, were decreased (P < 0.02). PEG and calcium hydroxide additives decreased the rumen and total tract digestibility of the DM of PSP (P < 0.006 and P < 0.02, respectively). Urea appeared to be the most suitable chemical agent for ensiling PSP because it decreased the TP and TT contents of PSP, did not affect punicalagin A and EA content, and improved rumen and total tract digestibility of the DM of PSP.