Resistant starch is defined as the total amount of starch and the products of starch degradation that resists digestion in the small intestine. Starches that were able to resist the digestion will arrive at the colon where they will be fermented by the gut microbiota, producing a variety of products which include short chain fatty acids that can provide a range of physiological benefits. There are several factors that could affect the resistant starch content of a carbohydrate which includes the starch granule morphology, the amylose–amylopectin ratio and its association with other food component. One of the current interests on resistant starch is their potential to be used as a prebiotic, which is a non-digestible food ingredient that benefits the host by stimulating the growth or activity of one or a limited number of beneficial bacteria in the colon. A resistant starch must fulfill three criterions to be classified as a prebiotic; resistance to the upper gastrointestinal environment, fermentation by the intestinal microbiota and selective stimulation of the growth and/or activity of the beneficial bacteria. The market of prebiotic is expected to reach USD 198 million in 2014 led by the export of oligosaccharides. Realizing this, novel carbohydrates such as resistant starch from various starch sources can contribute to the advancement of the prebiotic industry.

Aims The concept of using specific dietary components to selectively modulate the gut microbiota to confer a health benefit, defined as prebiotics, originated in 1995. In 2018, a group of scientists met at the International Scientific Association for Probiotics and Prebiotics annual meeting in Singapore to discuss advances in the prebiotic field, focussing on issues affecting functionality, research methodology, and geographical differences. Methods and Results The discussion ranged from examining scientific literature supporting the efficacy of established prebiotics, to the prospects for establishing health benefits associated with novel compounds, isolated from different sources. Conclusions While many promising candidate prebiotics from across the globe have been highlighted in preliminary research, there are a limited number with both demonstrated mechanism of action and defined health benefits as required to meet the prebiotic definition. Prebiotics are part of a food industry with increasing market sales, yet there are great disparities in regulations in different countries. Identification and commercialisation of new prebiotics with unique health benefits means that regulation must improve and remain up‐to‐date so as not to risk stifling research with potential health benefits for humans and other animals. Significance and Impact of Study This summary of the workshop discussions indicates potential avenues for expanding the range of prebiotic substrates, delivery methods to enhance health benefits for the end consumer, and guidance to better elucidate their activities in human studies.

The role of structure and molecular weight in fermentation selectivity in linear α-1,6 dextrans and dextrans with α-1,2 branching was investigated. Fermentation by gut bacteria was determined in anaerobic, pH-controlled fecal batch cultures after 36 h. Inulin (1%, wt/vol), which is a known prebiotic, was used as a control. Samples were obtained at 0, 10, 24, and 36 h of fermentation for bacterial enumeration by fluorescentin situhybridization and short-chain fatty acid analyses. The gas production of the substrate fermentation was investigated in non-pH-controlled, fecal batch culture tubes after 36 h. Linear and branched 1-kDa dextrans produced significant increases inBifidobacteriumpopulations. The degree of α-1,2 branching did not influence theBifidobacteriumpopulations; however, α-1,2 branching increased the dietary fiber content, implying a decrease in digestibility. Other measured bacteria were unaffected by the test substrates except for theBacteroides-Prevotellagroup, the growth levels of which were increased on inulin and 6- and 70-kDa dextrans, and theFaecalibacterium prausnitziigroup, the growth levels of which were decreased on inulin and 1-kDa dextrans. A considerable increase in short-chain fatty acid concentration was measured following the fermentation of all dextrans and inulin. Gas production rates were similar among all dextrans tested but were significantly slower than that for inulin. The linear 1-kDa dextran produced lower total gas and shorter time to attain maximal gas production compared to those of the 70-kDa dextran (branched) and inulin. These findings indicate that dextrans induce a selective effect on the gut flora, short-chain fatty acids, and gas production depending on their length.

Acacia gum (AG) is a branched-polysaccharide gummy exudate that consists of arabinose and galactose. The traditional practice in African-Middle Eastern countries uses this gum as medicine. Traditional use of AG is to treat stomach disease, which can be a potential functional food. In this research, commercially available AG from Acacia senegal and Acacia seyal was investigated as the prebiotic. The experiment employed a pH-controlled in vitro colon model inoculated with human fecal microbiota to mimic the human colon. Fermentation samples at 0, 6, 12, and 24 h were brought for short-chain fatty acid (SCFA) analysis using high-performance liquid chromatography and bacterial enumeration via fluorescent in situ hybridization. Results showed that AG significantly promotes Bifidobacteria proliferation similar to fructo-oligosaccharides (FOS) while inhibiting the Clostridium histolyticum group, commonly associated with gut dysbiosis. Acetate, propionate, and butyrate showed a similar trend to FOS (p > 0.05). The AG shows potential against gut dysbiosis, as it promotes gut-probiotics, through modulation of microbial population and SCFA production, especially butyrate.