Table 3.
Influence of olive cake (OC) processing on gas production parameters, dry matter effective degradability (DMED) and fermentation parameters in a 24-h in vitro fermentation of OC samples.
| Item | OC Type 1 | SEM 2 | p-Value | ||
|---|---|---|---|---|---|
| Crude OC (n = 25) | Exhausted OC (n = 9) | Cyclone OC (n = 8) | |||
| Gas production parameters 2 | |||||
| PGP (mL/g dry matter) | 64.5 a | 78.1 b | 74.4 ab | 3.67 | 0.008 |
| c (h−1) | 0.048 b | 0.054 b | 0.040 a | 0.0022 | <0.001 |
| Lag (h) | 0.16 | 0.21 | 0.33 | 0.091 | 0.208 |
| AGPR (mL/h) | 2.23 a | 3.07 b | 2.13 a | 0.182 | <0.001 |
| DMED (g/kg DM) | 208 a | 245 b | 217 ab | 10.1 | 0.025 |
| Fermentation parameters | |||||
| Total volatile fatty acids (VFA; mmol/g DM) | 3.35 | 3.57 | 3.56 | 0.090 | 0.067 |
| Molar proportions of VFA (mol/100 mol) | |||||
| Acetate (Ac) | 61.8 | 62.1 | 62.2 | 0.24 | 0.351 |
| Propionate (Pr) | 21.4 | 21.7 | 21.6 | 0.24 | 0.642 |
| Butyrate | 11.0 | 11.1 | 10.7 | 0.15 | 0.263 |
| Minor VFA 3 | 5.79 b | 5.16 a | 5.46 ab | 0.15 | 0.003 |
| Ac/Pr (mol/mol) | 2.92 | 2.89 | 2.91 | 0.036 | 0.854 |
| NH3–N (mg/L) | 222 b | 207 a | 222 b | 6.3 | 0.004 |
| FOM (g/kg organic matter) 4 | 311 a | 333 b | 338 b | 8.6 | 0.025 |
a,b Within each parameter, mean values with different superscripts differ (p < 0.05). 1 Crude OC: samples were dried and pelletized; Exhausted OC: samples were dried and subjected to a second oil extraction using hexane; Cyclone OC: samples were obtained from cyclone decanters during drying COC. n = number of samples. 2 PGP: potential gas production; c: fractional rate of gas production; Lag: time until the production of gas begins; AGPR: the average gas production rate until half of the PGP has been reached; FOM: fermented organic matter, DMED was calculated for a rumen passage rate of 0.042 per h. 3 Calculated as the sum of isobutyrate, isovalerate and valerate. 4 Fermented organic matter calculated from VFA production as described by Demeyer (1991).