This study evaluated short-chain fatty acid (SCFA) production from purified fiber sources when fermented in vitro using pig cecal contents as an inoculum. Fiber sources of interest were inulin from chicory root (native and long-chain inulin with 90 and 98% fiber, respectively), pectin from citrus peel (high methoxyl pectin), resistant starch (native starch), potato starch (commercial grade), and β-glucan (β-1,3;β-1,6 yeast-derived). Cellulose and cornstarch were used as indigestible and highly digestible carbohydrates, respectively. Triplicate samples of substrates (2 g) were subjected to enzymatic hydrolysis with pepsin and pancreatin for 6 h. Subsequently, hydrolyzed residues (200 mg) were incubated under anaerobic conditions at 39°C with 30 mL solution of cecal inoculum collected from 3 sows fed a standard commercial diet and buffered mineral solution. After 48 h of incubation, solutions from fermented samples were analyzed for pH, SCFA, and branched-chain fatty acids (BCFA) using gas-liquid chromatography. Enzymatic hydrolysis had no effect on digestion of β-glucan, but total SCFA concentration after fermentation was highest (26.13 mmol/g) followed by resistant starch (22.61 mmol/g) and potato starch (22.20 mmol/g) and was lowest for cellulose (13.91 mmol/g). In contrast, native inulin was highly digested during enzymatic hydrolysis, resulting in the lowest substrate available for fermentation (11.84% DM) and the highest pH (5.98). Enzymatic hydrolysis and fermentation of resistant starch increased (P< 0.001) concentrations of acetate (0.60 mg/g), whereas potato starch and β-glucan yielded more butyrate (0.60 and 0.54 mg/g respectively), and β-glucan resulted in greater (P< 0.001) propionate concentrations (0.69 mg/g). Pectin resulted in the highest fermentation (82.38% DM disappearance) and the lowest pH (4.03) compared to the other fiber sources (P< 0.001) and yielded the lowest BCFA concentration (1.89 mM, P< 0.001).
Results suggest that fermentation of resistant starch, potato starch, and β-glucan produced higher SCFA concentrations, while pectin resulted in a decreased pH of fermentation solution.