Porcine in vitro fermentation characteristics of canola co-products in neutral and acidic fermentation medium pH

An in vitro study was conducted to determine effects of reducing pH of porcine in vitro fermentation medium on compositions of glucosinolate degradation products and porcine in vitro fermentation characteristics for solvent-extracted canola meal (SECM) and cold-pressed canola cake (CPCC). Two canola co-products were subjected to porcine in vitro fermentation for 72 h. Accumulated gas production during microbial fermentation was recorded and modeled to estimate kinetics of gas production. Glucosinolate degradation products after microbial fermentation were determined and fermentation medium pH after incubation was recorded. Total and individual volatile fatty acids (VFA) concentrations per unit weight of dry matter (DM) of feedstuffs were determined. On DM basis, SECM and CPCC contained 6.15 and 11.1 µmol/g of glucosinolates, respectively. Goitrin concentration for CPCC was lower (P < 0.05) than that for SECM. Isothiocyanate and indole-3-acetonitrile concentrations for CPCC were lower (P < 0.05) than those for SECM, whereas thiocyanate concentration for CPCC was greater (P < 0.05) than that for SECM. A reduction in fermentation medium pH from 6.2 to 5.2 increased (P < 0.05) goitrin and indole-3-acetonitrile concentrations and decreased (P < 0.05) isothiocyanates concentration for SECM, but did not affect concentration of these 2 glucosinolate degradation products for CPCC. Fermentation medium pH after in vitro fermentation for SECM tended to be greater (P = 0.081) than that for CPCC. Canola co-product type and fermentation medium pH did not interact on gas production parameters. However, a reduction in fermentation medium pH from 6.2 to 5.2 resulted in increased (P < 0.05) lag time and reduced (P < 0.05) fractional rate of degradation and total gas production. Canola co-product type and fermentation medium pH did not interact on total or individual VFA production per gram of DM of feedstuff fermented. However, reducing fermentation medium pH from 6.2 to 5.2 increased (P < 0.05) total VFA and acetate productions, and tended to reduce (P = 0.083) branched-chain VFA production SECM and CPCC. In conclusion, a reduction in fermentation medium pH from 6.2 to 5.2 resulted in increased production of goitrin and indole-3-acetonitriles from SECM-derived glucosinolates, but did not affect production of thiocyanate from SECM-derived glucosinolates. Glucosinolates in CPCC were less affected by the fermentation medium pH used in the current study. It appears that there are other factors other than pH that affect the degradation of canola-derived glucosinolates by microorganisms from hindgut of pigs.