Structure and function of non-digestible carbohydrates in the gut microbiome

Together with proteins and fats, carbohydrates are one of the macronutrients in the human diet. Digestible carbohydrates, such as starch, starch-based products, sucrose, lactose, glucose and some sugar alcohols and unusual (and fairly rare) α-linked glucans, directly provide us with energy while other carbohydrates including high molecular weight polysaccharides, mainly from plant cell walls, provide us with dietary fibre. Carbohydrates which are efficiently digested in the small intestine are not available in appreciable quantities to act as substrates for gut bacteria. Some oligo- and polysaccharides, many of which are also dietary fibres, are resistant to digestion in the small intestines and enter the colon where they provide substrates for the complex bacterial ecosystem that resides there. This review will focus on these non-digestible carbohydrates (NDC) and examine their impact on the gut microbiota and their physiological impact. Of particular focus will be the potential of non-digestible carbohydrates to act as prebiotics, but the review will also evaluate direct effects of NDC on human cells and systems.

Analysis of B-6 vitamers in human milk by reverse-phase liquid chromatography

A simple, accurate reverse-phase high performance liquid chromatography (RPLC) method was introduced for the analysis of B-6 vitamers in human milk. The assay consisted of a phosphate buffer (pH 2.9) delivered isocratically through 5 micron ODS column packing, followed by post-column bisulfite derivatization to enhance the detection of PLP (and to a minor extent PL). The vitamers were detected using a fluorescence spectromonitor. Sample run time was less than 30 min. The sensitivity of the method was such that PL, PN, and PLP were detectable to 30 pmol/ml milk and PM and PMP to 5 pmol/ml milk. Total vitamin B-6 content in milk analyzed by RPLC correlated well with the microbiological assay. B-6 vitamer distribution in human milk was similar to values obtained from two different ion-exchange HPLC systems. The RPLC procedure is simpler and faster than the HPLC systems and is suggested for future use in analysis of B-6 vitamer concentrations in human milk.

Effect of maternal vitamin B-6 restriction on pyridoxal phosphate concentrations in developing regions of the central nervous system in rats

The effect of maternal vitamin B-6 deficiency on concentrations of pyridoxal phosphate (PLP) within four different regions of the central nervous system (CNS) of progeny, the corpus striatum (CS), hypothalamus (H), cerebellum (C), total brain and first cervical segment (C-1) of the spinal cord was determined at 7, 15, 21 and 50 days of age. PLP concentrations in each CNS region, as well as in total brain at 15, 21 and 50 days postnatally, paralleled the level of vitamin B-6 in the deficient (0.6, 0.8, 1.0 mg pyridoxine . HCl per kilogram diet) and control diets (7.0 mg pyridoxine . HCl per kilogram diet). By 21 days of age, PLP concentrations had essentially plateaued in CNS regions of controls, whereas in the vitamin B-6-restricted groups, a significant catch-up in concentration was observed between 21 and 50 days of age in all CNS regions except C-1 of the spinal cord. Throughout postnatal development, PLP concentrations in the C-1 region of spinal cord and in hypothalamus appeared least affected by vitamin B-6 restriction and levels in CS and C were most affected. These findings suggested that the mechanism for intracellular trapping of B-6 vitamers may develop in a caudal to rostral direction within the CNS.