Deactivation of tannins in raisin stalk by polyethylene glycol-600: Effect on degradation and gas production in vitro

Abstract

An experiment was conducted to assess the effects of polyethylene glycol (PEG-6000) and urea on dry and organic matter digestibility (IVDMD and IVOMD, respectively) and gas production in vitro. Raisin stalk contained 8.6% crude protein, 85% dry matter, 7% ash, 13.95% total extractable phenol (TEPH) and 2.13% total extractable tannin (TET). The experimental treatments were: raisin with no supplementation as control (C); supplemented with 3% urea (U 3%), 5% urea (U 5%) or 3% urea plus 5% PEG (U-PEG) per DM. The rumen liquor fluid was obtained from two ruminal-cannulated fat-tailed sheep. TEPH and TET were determined and in vitro incubation was also conducted. The results indicated that the PEG increased IVOMD and IVDMD. The gas produced from time 0 to 3 and 3 to 6 h of incubation were significantly higher in PEG treatment than that of other groups (P < 0.05). The U-PEG treatment increased the total gas production in 96 h, but it was not statistically significant (P = 0.06) Gas production in 96 h incubation using 300 mg fresh sample was significantly higher than 200 mg sample (P < 0.05). It is concluded that the negative effect of tannin on DM and OM digestibility and also gas production of raisin stalk in vitro could be alleviated by PEG treatment.

Key words: Raisin stalk, tannin, polyethylene glycol (PEG), urea, gas production, digestibility, in vitro.