In vitro fermentation characteristics of acacia fiber using feline fecal inoculum

Acacia fiber is a soluble fiber often used as a processing aid in pet foods. The objective of this experiment was to evaluate the fermentation characteristics of acacia fiber, inulin, pectin (positive control), and cellulose (negative control) using an in vitro fermentation system and feline fecal inoculum. Triplicate samples of each fiber were fermented for 0, 6, 12, and 18 h, with short-chain fatty acids (SCFA), pH, and microbiota measured at each time point. Blank-corrected data were analyzed using PROC GLIMMIX of SAS, with significance set at P ≤ 0.05. Significant (P < 0.01) fiber × time interactions were observed for pH change, gas and SCFA production, and microbiota populations. Pectin and inulin had greater (P < 0.01) gas production than acacia fiber and cellulose. Inulin had the greatest pH reduction, followed by pectin, both of which had greater pH reductions (P < 0.01) than acacia fiber and cellulose. Acacia fiber had a small reduction in pH, being lower than cellulose after 12 h. Total SCFA production, including acetate, propionate, and butyrate, was higher (P < 0.01) in pectin and inulin than acacia fiber and cellulose. However, acacia fiber had greater (P < 0.01) total SCFA, acetate, and propionate production than cellulose after 12 h. Bacterial alpha diversity metrics increased (P < 0.01) during acacia fiber fermentation and decreased (P < 0.01) during inulin and pectin fermentation. Bacterial beta diversity shifted over time and showed separate clustering of bacterial communities among the different fiber substrates evaluated. The relative abundances of predominant (% sequences > 1%) bacterial genera were affected by significant fiber × time interactions. Specifically, acacia fiber had a greater (P < 0.01) increase in Bacteroides, Blautia, and Faecalibacterium than other fibers. Inulin had a greater (P < 0.01) increase in Collinsella, Prevotella, Megamonas, Holdemanella, Blautia, and Faecalibacterium, whereas pectin had a greater (P < 0.01) increase in Bifidobacterium, Lactobacillus, Phascolarctobacterium, and Succinivibrio. These results suggest that acacia fiber is moderately fermentable, resulting in low gas and SCFA production, greater bacterial diversity, and microbiota shifts. Although positive responses were observed in vitro, research in live animals is necessary to confirm potential benefits in felines.