The course of fermentation of starch with the addition of different types of tannins

Four different concentrations (0 (control), 0.33, 0.67 and 1.33 mg ml-1 medium) of three tannin extracts (chestnut (F75) and quebracho (QUE) tannin extracts and tannic acid (TAK) were used to investigate their effect on the kinetics of in vitro fermentation of starch. Gas production was measured at 0, 2, 4, 6, 8, 10, 12, 24, 36, 48, 72 and 96 h after the start of incubation. Gompertz model was used to estimate kinetic parameters 'B' (total potential gas production), 'C' (relative degradation rate) and 'A' (constant decay in relative degradation rate). First and second derivatives of Gompertz model were used to calculate the maximum fermentation rate (MFR) and time of maximum fermentation rates (TMFR). Addition of F75 (507.8 ml g-1 DM) and QUE (474.2 ml g-1 DM) significantly decreased (P 0.05) total potential gas production compared to control (528.4 ml g-1 DM). On contrary, the addition of TAK (560.5 ml g-1 DM) significantly increased total potential gas production. Maximum fermentation rate of starch (50.6 ml h-1) occurred after almost 9 hours of incubation. The addition of tannin extracts significantly increased TMFR; this increase was greatest when 0.33 mg of tannin extracts were added to the medium. Type and concentration of tannin extracts had significant effect (P 0.01) on maximum fermentation rate of starch. The lowest reduction in MFR was determined when F75 was used (MFR reduced to 42.0 ml h-1), while it was reduced to 38.1 ml h-1 when TAK and 34.7 ml g-1 when QUE were used. The greatest reduction in MFR was determined when the concentration of 0.67 mg of tannin extracts/ml medium was used.