To evaluate the fermentation properties of oligosaccharides derived from pectins and their parent polysaccharides, a 5-ml-working-volume, pH-and temperature-controlled fermentor was tested. Six pectic oligosaccharides representing specific substructures found within pectins were prepared. These consisted of oligogalacturonides (average degrees of polymerization [DP] of 5 and 9), methylated oligogalacturonides (average DP of 5), oligorhamnogalacturonides (average DP of 10 as a disaccharide unit of galacturonic acid and rhamnose), oligogalactosides (average DP of 5), and oligoarabinosides (average DP of 6). The influence of these carbohydrates on the human fecal microbiota was evaluated. Use of neutral sugar fractions resulted in an increase in Bifidobacterium populations and gave higher organic acid yields. The Bacteroides-Prevotella group significantly increased on all oligosaccharides except oligogalacturonides with an average DP of 5. The most selective substrates for bifidobacteria were arabinan, galactan, oligoarabinosides, and oligogalactosides.Pectins are complex plant heteropolysaccharides consisting in the main of four types of carbohydrate structure. These are partially methyl and/or acetyl esterified polygalacturonic acid (PGalA), rhamnogalacturonan type I (RG I), xylogalacturonan, and rhamnogalacturonan type II (RG II). PGalA is a linear homopolymer of ␣-(1,4)-galacturonic acid. Xylogalacturonan consists of a PGalA backbone with xylose bound to galactopyranosyluronic acid (GalpA) at C-3. RG I and RG II comprise the so-called "hairy regions" due to their branched structures. The -4-␣-D-GalAp-1,2-␣-L-Rhap-1-disaccharide sequence constitutes the main chain of RG I, with substitutions at position 4 of the rhamnose residues as well as acetylation on C-2 or C-3 of the galacturonic acid. Side chains are ␣-(1,5)-arabinan, ␤-(1,4)-galactan, and arabinogalactan type I. RG II is very complex, but it is believed to be the most conserved part of pectin. This molecule has PGalA as a backbone and is branched with rhamnose and other rare sugars such as apiose, 2-O-methylxylose, and 2-O-methylfucose (31).The biological effects of pectins have been studied extensively, and they are reported to be highly fermentable dietary fibers (5). Apart from their complexity and heterogeneity, both pectins and their derivatives have been investigated for many other potential health benefits. Pectins are found in oriental medicinal herbs and are thought to be responsible for their therapeutic effects (18,27). Studies to date indicate that different regions of pectins may mediate the different health effects. For example, modified citrus pectin may control the progress of malignancy (12) or induce apoptosis in cancer cell lines (20,29). In terms of the selectivity of fermentation by fecal bacteria, pectic oligosaccharides had greater selectivity toward bifidobacteria in batch cultures than the parent pectin (24,25,30).Many plant by-products are rich in pectins, which could possibly be sources of active pectic compounds and may prove ...

Shiga toxin (Stx)-producing, food-contaminating Escherichia coli (STEC) is a major health concern. Plant-derived pectin and pectic-oligosaccharides (POS) have been considered as prebiotics and for the protection of humans from Stx. Of five structurally different citrus pectic samples, POS1, POS2 and modified citrus pectin 1 (MCP1) were bifidogenic with similar fermentabilities in human faecal cultures and arabinose-rich POS2 had the greatest prebiotic potential. Pectic oligosaccharides also enhanced lactobacilli growth during mixed batch faecal fermentation. We demonstrated that all pectic substrates were anti-adhesive for E. coli O157:H7 binding to human HT29 cells. Lower molecular weight and deesterification enhanced the anti-adhesive activity. We showed that all pectic samples reduced Stx2 cytotoxicity in HT29 cells, as measured by the reduction of human rRNA depurination detected by our novel TaqMan-based RT-qPCR assay, with POS1 performing the best. POS1 competes with Stx2 binding to the Gb3 receptor based on ELISA results, underlining the POS anti-STEC properties.