There are few studies on the assessment of digestibility of nondigestible carbohydrates, despite their increasingly important role in human health. In vitro digestibility of a range of dietary carbohydrates classified as digestible (maltose, sucrose, and lactose), well-recognized (lactulose, fructooligosaccharides (FOS), and two types of galactooligosaccharides (GOS) differing in the predominant glycosidic linkage), and potential (lactosucrose and GOS from lactulose, OsLu) prebiotics using a rat small intestinal extract (RSIE) under physiological conditions of temperature and pH is described. Recognized and potential prebiotics were highly resistant to RSIE digestion although partial hydrolysis at different extents was observed. FOS and lactulose were the most resistant to digestion, followed closely by OsLu and more distantly by both types of GOS and lactosucrose. In GOS, β(1 → 6) linkages were more resistant to digestion than β(1 → 4) bonds. The reported in vitro digestion model is a useful, simple, and cost-effective tool to evaluate the digestibility of dietary oligosaccharides.

The suitability of artichoke and sunflower by-products as renewable sources of pectic compounds with prebiotic potential was evaluated by studying their ability to modulate the human faecal microbiota in vitro. Bacterial populations and short-chain fatty acid (SCFA) production were measured. Reduction of the molecular weight of artichoke pectin resulted in greater stimulation of the growth of Bifidobacterium, Lactobacillus and Bacteroides/Prevotella, whilst this effect was observed only in Bacteroides/Prevotella for sunflower samples. In contrast, the degree of methoxylation did not have any impact on fermentability properties or SCFA production, regardless of the origin of pectic compounds. Although further in vivo studies should be conducted, either pectin or enzymatically-modified pectin from sunflower and artichoke by-products might be considered as prebiotic candidates for human consumption showing similar ability to promote the in vitro growth of beneficial gut bacteria as compared to well-recognized prebiotics such as inulin or fructo-oligosaccharides.

During the last years, there is an increasing interest toward the potential prebiotic properties of pectin. However, most of the studies have been carried out in batch in vitro assays without a previous gastrointestinal digestion. In vivo investigations provide the best models for studying the influence of these compounds on the activity of microbiota. However, due to the difficulty of this type of assays, in vitro multistage dynamic models are presented as a good alternative. Thus, the behaviour during digestion and potential prebiotic properties of a commercial citrus pectin was examined using a Dynamic Gastrointestinal Simulator (simgi®) model for the human gut, which allows to study the behaviour of compounds in five different compartments (stomach, small intestine, ascending, transverse and descending colon). A remarkable nondigestibility of citrus pectin in the upper gastrointestinal tract was observed following its monitoring by HPLC-ELSD which determined that ~88% of fed citrus pectin remained intact during its transit through the stomach and small intestine. Fermentation of pectin stimulated the growth of beneficial bacteria such as Bifidobacterium spp, Bacteroides spp and Faecalobacterium prausnitzii. A high increase of short-chain fatty acids (SCFA) was observed, in concordance with the bacterial growth, especially in acetate and butyrate, which was produced due to direct fermentation of pectin or by cross-feeding interaction between bacteria. As a consequence of the pH decrease, the levels of ammonia were also decreased. This is the first study on the digestibility and fermentation of pectin carried out in a complex dynamic gastrointestinal simulator, being of special relevance the results obtained for F. prausnitzii.