Prebiotics function

Following the PASSCLAIM recommendation (69), studies in mice were recommended to substantiate conclusions related to immunological effects of dietary compounds. As for the prebiotic function, the most systematic studies were performed with a mixture of GOS/lcFOS. The experimental data have been intensively reviewed recently by Vos et al. (70). 

FIGURE 5.1 Health effects associated with dietary supplementation with prebiotic functional foods. 

Calame W, Weseler AR, Viebke C, Flynn C, Siemensma AD. Gum arable establishes prebiotic functionality in healthy human volunteers in a dose-dependent manner. Br J Nutr. 2008 100 1269-1275. 

The selective utilization of prebiotics by some, but not all, of the resident species alters the assemblages, densities and metabolic activities of the GIT bacteria. Of importance is the ability of prebiotics to increase the proportion of the resident bacteria represented by the lactic acid producing bacteria (LAB), resulting in changes of GIT and systemic functions (Swanson et al.. 

ROBERFROID M B (2000) Prebiotics and probiotics are they functional foods dm J Clin Nutr 11 1682S-90S. 

Among the various theories and hypotheses concerning the prebiotic synthesis of biomolecules, processes occurring at the surfaces of minerals are becoming much more popular. The minerals can serve three different functions ... 

However, the question must always be asked as to whether these processes could have taken place on the primordial Earth in its archaic state. The answer requires considerable fundamental consideration. Strictly speaking, most of the experiments carried out on prebiotic chemistry cannot be carried out under prebiotic conditions , since we do not know exactly what these were. In spite of the large amount of work done, physical parameters such as temperature, composition and pressure of the primeval atmosphere, extent and results of asteroid impacts, the nature of the Earth s surface, the state of the primeval ocean etc. have not so far been established or even extrapolated. It is not even sure that this will be possible in the future. In spite of these difficulties, attempts are being made to define and study the synthetic possibilities, on the basis of the assumed scenario on the primeval Earth. Thus, for example, in the case of the SPREAD process, we can assume that the surface at which the reactions occur could not have been an SH-containing thiosepharose, but a mineral structure of similar activity which could have carried out the necessary functions just as well. The separation of the copy of the matrix could have been driven by a periodic temperature change (e.g., diurnal variation). For his models, H. Kuhn has assumed that similar periodic processes are the driving force for some prebiotic reactions (see Sect. 8.3). 

Pyrite is not only one of the key compounds in Wachtershauser s theory, but could also have fulfilled an important function for phosphate chemistry in prebiotic syntheses. A group in Rio de Janeiro studied the conditions for phosphate sorption and desorption under conditions which may have been present in the primeval ocean. In particular, the question arises as to the enrichment of free, soluble inorganic phosphate (Pi), which was probably present in low concentrations similar to those of today (10 7-10 8M) (Miller and Keffe, 1995). Experiments show that acid conditions favour sorption at FeS2, while a weakly alkaline milieu works in an opposite manner. Sorption of Pi can be favoured by various factors, such as hydrophobic coating of pyrite with molecules such as acetate, which could have been formed in the vicinity of hydrothermal systems, or the neutralisation of mineral surface charges by Na+ and K+. 

The physiologist de Duve concentrated his efforts on a material link between the prebiotic phase of the primeval Earth and the state of development at which RNA (or a similar type of molecule) determined the further progress of the evolution process. In particular, this connecting link needed to have been able to transfer chemical energy, since without such a procedure, the RNA synthesis appears impossible. The molecular species which Christian de Duve favours for this important function is that of the thioesters. The exact reasoning as to why this is the case is discussed in detail in his book Vital Dust Life As a Cosmic Imperative (de Duve, 1996). 

The manufacture of liposomes (which is, for example, carried out by the cosmetics industry) is a complex technical process. Thus, the question arises as to whether a simple mechanism for liposome formation exists which could have functioned under plausible prebiotic conditions. More than 20 years ago, Deamer and co-workers... 

Throughout history, mankind has always been interested in naturally occurring compounds from prebiotic, microbial, plants and animals sources. Various extracts of flowers, plants and insects have been used for isolating compounds whose task, color and odor could be used for various purposes. Many natural products, such as plant hormones, have a regulatory role, while others function as chemical defense against pests. The role of certain compounds is to act as chemical messengers, such as sex-attractants (pheromones) in insects, terrestrial and marine animals and humans. What is the origin of natural products ... 

Having highlighted some of the data and issues about the prebiotic chemistry of low-molecular-weight compounds, let s now turn to the functional long chains -mostly proteins and nucleic acids. The first part of this chapter is devoted to the prehiotic chemistry of hiopolymers, the second part, which will necessarily be more speculative, to ideas of conceiving the very origin of macromolecular sequences. 

A self-replicating polymer would quickly use up available supplies of precursors provided by the relatively slow processes of prebiotic chemistry. Thus, from an early stage in evolution, metabolic pathways would be required to generate precursors efficiently, with the synthesis of precursors presumably catalyzed by ri-bozymes. The extant ribozymes found in nature have a limited repertoire of catalytic functions, and of the ribozymes that may once have existed, no trace is left. To explore the RNA world hypothesis more deeply, we need to know whether RNA has the potential to catalyze the many different reactions needed in a primitive system of metabolic pathways. 

There is a growing interest in the inclusion of soluble fibre into the diet to help improve health. This is extending to drinks as well, with such fibre being added to milk- and fruit-based products such as smoothies . One source of soluble fibre which has attracted attention over the last few years is inulin or oligofiuc-tans. Inulin consists of oligosaccharides that are extracted from chicory or Jerusalem artichokes and that are claimed to improve colon function and to have prebiotic properties, enhancing the working of the gut. Inulin is a complex carbohydrate which can be assayed in a number of different ways. However, there are two published methods in the AO AC manual for its analysis (997.08 and 999.03). 

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