Selective fermentation of gentiobiose-derived oligosaccharides by human gut bacteria and influence of molecular weight

Gentiooligosaccharides and alternansucrase gentiobiose acceptor products were fractionated by their degree of polymerization (DP) on a Bio-Gel P2 column. Fractions were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectroscopy, and incubated with human faecal bacteria under anaerobic conditions at 37 degrees C. The growth of predominant gut bacteria on the oligosaccharides was evaluated by fluorescence in situ hybridization and a prebiotic index (PI) was calculated. Lower DP gentiooligosaccharides (DP2-3) showed the highest selectivity (PI of 4.89 and 3.40, respectively), whereas DP4-5 alternansucrase gentiobiose acceptor products generated the greatest values (PI of 5.87). The production of short-chain fatty acids was also determined during the time course of the reactions. The mixture of DP6-10 alternansucrase gentiobiose acceptor products generated the highest levels of butyric acid but the lowest levels of lactic acid. Generally, for similar molecular weights, alternansucrase gentiobiose acceptor products gave higher PI values than gentiooligosaccharides.

Influence of glycosidic linkages and molecular weight on the fermentation of maltose-based oligosaccharides by human gut bacteria

A structure-function study was carried out to increase knowledge of how glycosidic linkages and molecular weights of carbohydrates contribute toward the selectivity of fermentation by gut bacteria. Oligosaccharides with maltose as the common carbohydrate source were used. Potentially prebiotic alternansucrase and dextransucrase maltose acceptor products were synthesized and separated into different molecular weights using a Bio-gel P2 column. These fractions were characterized by matrix-assisted laser desorption/ionization time-of-flight. Nonprebiotic maltooligosaccharides with degrees of polymerization (DP) from three to seven were commercially obtained for comparison. Growth selectivity of fecal bacteria on these oligosaccharides was studied using an anaerobic in vitro fermentation method. In general, carbohydrates of DP3 showed the highest selectivity towards bifidobacteria; however, oligosaccharides with a higher molecular weight (DP6-DP7) also resulted in a selective fermentation. Oligosaccharides with DPs above seven did not promote the growth of "beneficial" bacteria. The knowledge of how specific structures modify the gut microflora could help to find new prebiotic oligosaccharides.

Prebiotic properties of alternansucrase maltose-acceptor oligosaccharides

alpha-(1-6) and alpha-(1-3)-linked oligosaccharides were obtained from the reaction between sucrose and maltose, catalyzed by an alternansucrase isolated from Leuconostoc mesenteroides NRRL B-21297 and separated using a Bio-Gel P2 column in six fractions. Fractions 1, 2, and 3 were mainly composed of DP3, DP4, and DP5, respectively. However, fractions 4, 5, and 6 consisted of mixtures from DP5 to IDP9, and they are identified here as DP5.7, DP6.7, and DP7.4, respectively. Potential prebiotic properties of these oligosaccharides were tested using pure and mixed cultures. Generally, in pure studies, most of the tested bacteria failed to grow or grew poorly using the DP6.7 and DP7.4 fractions and showed the greatest growth on DP3. Growth of fecal bacteria on the maltose-acceptor products was tested following an in vitro fermentation method. DP3 showed the highest prebiotic effect, followed by DP4 and DP6.7, whereas DP7.4 did not present any prebiotic activity.

Potential for the development of prebiotic oligosaccharides from biomass

Waste biomass contains a multitude of complex carbohydrate molecules. These carbohydrates can be considered as a resource for the development of novel prebiotic oligosaccharides which may have better functionality than those currently established on the market. Enhanced persistence of the prebiotic effect along the colon, antipathogen effects, and more closely targeted prebiotics, might all be possible starting from plant polysaccharides. Of particular interest for the development of novel prebiotics are oligosaccharides from arabinoxylans and pectins. Oligosaccharides derived from the breakdown of both classes have received increased research attention recently. The development of prebiotics based upon biomass will demand the development of new manufacturing technologies.

Pectic oligosaccharides as prebiotics

Pectic oligosaccharides were observed to have bifidogenic prebiotic properties. Pectic oligosaccharides were also found to possess anti-adhesive properties for food pathogen toxins and they stimulated apoptosis of colon cancer cells. Orange peel albedo (white part) was a good source of pectic oligosaccharides with prebiotic properties. Microwave and autoclave extraction produced pectic oligosaccharides with higher degrees of polymerization than those produced with an ultrafiltration dead-end membrane enzyme reactor. We propose that these larger orange albedo pectic oligosaccharides may have greater persistence through the colon, making them excellent candidates for second generation prebiotic product development.

‘Once a miner, always a miner’: Poverty and livelihood diversification in Akwatia, Ghana

This paper offers an alternative viewpoint on why people choose to engage in artisanal mining – the low tech mineral extraction and processing of mainly precious metals and stones – for extended periods in sub-Saharan Africa. Drawing upon experiences from Akwatia, Ghana’s epicentre of diamond production since the mid-1920s, the analysis challenges the commonly-held view that the region’s people are drawn to artisanal mining solely because of a desire ‘to get rich quick’. A combination of events, including the recent closure of Ghana Consolidated Diamonds Ltd’s industrial-scale operation and decreased foreign investment in the country’s diamond industry over concerns of it potentially harbouring ‘conflict’ stones from neighbouring Coˆte D’Ivoire, has had a debilitating economic impact on Akwatia. In an attempt to alleviate their hardships, many of the town’s so-called ‘lifetime’ diamond miners have managed to secure employment in neighbouring artisanal gold mining camps. But their decision has been condemned by many of the country’s policymakers and traditional leaders, who see it solely as a move to secure ‘fast money’. It is argued here, however, that these people pursue work in surrounding artisanal gold mining communities mainly because of poverty, and that their decision has more to do with a desire to immerse in activities with which they are familiar, that offer stable employment and consistent salaries, and provide immediate debt relief. Misdiagnosis of cases such as Akwatia underscores how unfamiliar policymakers and donors are with the dynamics of ASM in sub-Saharan Africa.