Oil palm fiber extract as a fermentable functional ingredient: in vitro gastrointestinal carbohydrate hydrolysis, feline fecal fermentation, and microbiota-associated metabolite production

Abstract

Obesity-associated gastrointestinal disturbances in companion animals have increased interest in dietary ingredients that may modulate intestinal fermentation and microbial metabolism. This study evaluated the in vitro gastrointestinal digestion, fecal fermentation, microbiota responses, and metabolite production associated with oil palm fiber extract (OPF) in a feline gastrointestinal model. OPF, commercial feline diet (CFD), OPF-supplemented CFD (OPF+CFD), and commercial weight-control diet (WCD) were subjected to simulated gastrointestinal digestion followed by 24 h of anaerobic fecal fermentation. Fecal samples from nine cats were pooled to prepare a common inoculum. Carbohydrate hydrolysis of OPF following simulated gastrointestinal digestion was 4.01% ± 0.54%, indicating limited hydrolysis under the experimental conditions. Phenolic and flavonoid-equivalent responses were retained after digestion, although values exceeding 100% were interpreted as increased assay responses rather than recovery above the initial values. During fermentation, OPF was associated with increased concentrations of acetate, propionate, and butyrate, together with changes in branched-chain fatty acids. Microbiome profiling indicated treatment-associated changes in bacterial community composition and diversity patterns. LC-QTOF-MS analysis detected several phenolic-related metabolites in OPF-containing treatments after fermentation, including hydroxyphenylpropionic acid- and coumarin-related compounds. However, these metabolites were tentatively annotated, and their formation from specific OPF precursors was not directly demonstrated. Because each treatment was represented by a single fermentation vessel using the pooled fecal inoculum, analytical replicates were not considered independent biological replicates; consequently, microbiome and fermentation findings were interpreted descriptively. Overall, the results provide preliminary in vitro evidence that OPF can undergo gastrointestinal processing and subsequent fecal fermentation, with associated changes in fermentation metabolites and microbial community profiles. Further studies using independent donors, biological fermentation replicates, quantitative metabolite validation, and controlled feeding trials are required to establish the physiological relevance, efficacy, and safety of OPF in cats.