Electron attachment to SF6 and lifetimes of SF6- negative ions

We study the process of low-energy electron capture by the SF6 molecule. Our approach is based on the model of Gauyacq and Herzenberg [J. Phys. B 17, 1155 (1984)] in which the electron motion is coupled to the fully symmetric vibrational mode through a weakly bound or virtual s state. By tuning the two free parameters of the model, we achieve an accurate description of the measured electron attachment cross section and good agreement with vibrational excitation cross sections of the fully symmetric mode. An extension of the model provides a limit on the characteristic time of intramolecular vibrational relaxation in highly-excited SF6-. By evaluating the total vibrational spectrum density of SF6-, we estimate the widths of the vibrational Feshbach resonances of the long-lived negative ion. We also analyse the possible distribution of the widths and its effect on the lifetime measurements, and investigate nonexponential decay features in metastable SF6-.Comment: 22 pages, 10 figures, submitted to Phys. Rev.

Prebiotic effects: metabolic and health benefits

The different compartments of the gastrointestinal tract are inhabited by populations of micro-organisms. By far the most important predominant populations are in the colon where a true symbiosis with the host exists that is a key for well-being and health. For such a microbiota, 'normobiosis' characterises a composition of the gut 'ecosystem' in which micro-organisms with potential health benefits predominate in number over potentially harmful ones, in contrast to 'dysbiosis', in which one or a few potentially harmful micro-organisms are dominant, thus creating a disease-prone situation. The present document has been written by a group of both academic and industry experts (in the ILSI Europe Prebiotic Expert Group and Prebiotic Task Force, respectively). It does not aim to propose a new definition of a prebiotic nor to identify which food products are classified as prebiotic but rather to validate and expand the original idea of the prebiotic concept (that can be translated in 'prebiotic effects'), defined as: 'The selective stimulation of growth and/or activity(ies) of one or a limited number of microbial genus(era)/species in the gut microbiota that confer(s) health benefits to the host.' Thanks to the methodological and fundamental research of microbiologists, immense progress has very recently been made in our understanding of the gut microbiota. A large number of human intervention studies have been performed that have demonstrated that dietary consumption of certain food products can result in statistically significant changes in the composition of the gut microbiota in line with the prebiotic concept. Thus the prebiotic effect is now a well-established scientific fact. The more data are accumulating, the more it will be recognised that such changes in the microbiota's composition, especially increase in bifidobacteria, can be regarded as a marker of intestinal health. The review is divided in chapters that cover the major areas of nutrition research where a prebiotic effect has tentatively been investigated for potential health benefits. The prebiotic effect has been shown to associate with modulation of biomarkers and activity(ies) of the immune system. Confirming the studies in adults, it has been demonstrated that, in infant nutrition, the prebiotic effect includes a significant change of gut microbiota composition, especially an increase of faecal concentrations of bifidobacteria. This concomitantly improves stool quality (pH, SCFA, frequency and consistency), reduces the risk of gastroenteritis and infections, improves general well-being and reduces the incidence of allergic symptoms such as atopic eczema. Changes in the gut microbiota composition are classically considered as one of the many factors involved in the pathogenesis of either inflammatory bowel disease or irritable bowel syndrome. The use of particular food products with a prebiotic effect has thus been tested in clinical trials with the objective to improve the clinical activity and well-being of patients with such disorders. Promising beneficial effects have been demonstrated in some preliminary studies, including changes in gut microbiota composition (especially increase in bifidobacteria concentration). Often associated with toxic load and/or miscellaneous risk factors, colon cancer is another pathology for which a possible role of gut microbiota composition has been hypothesised. Numerous experimental studies have reported reduction in incidence of tumours and cancers after feeding specific food products with a prebiotic effect. Some of these studies (including one human trial) have also reported that, in such conditions, gut microbiota composition was modified (especially due to increased concentration of bifidobacteria). Dietary intake of particular food products with a prebiotic effect has been shown, especially in adolescents, but also tentatively in postmenopausal women, to increase Ca absorption as well as bone Ca accretion and bone mineral density. Recent data, both from experimental models and from human studies, support the beneficial effects of particular food products with prebiotic properties on energy homaeostasis, satiety regulation and body weight gain. Together, with data in obese animals and patients, these studies support the hypothesis that gut microbiota composition (especially the number of bifidobacteria) may contribute to modulate metabolic processes associated with syndrome X, especially obesity and diabetes type 2. It is plausible, even though not exclusive, that these effects are linked to the microbiota-induced changes and it is feasible to conclude that their mechanisms fit into the prebiotic effect. However, the role of such changes in these health benefits remains to be definitively proven. As a result of the research activity that followed the publication of the prebiotic concept 15 years ago, it has become clear that products that cause a selective modification in the gut microbiota's composition and/or activity(ies) and thus strengthens normobiosis could either induce beneficial physiological effects in the colon and also in extra-intestinal compartments or contribute towards reducing the risk of dysbiosis and associated intestinal and systemic pathologies

Wplyw synbiotykow na biodostepnosc magnezu z diety u szczurow

Products containing pro- and prebiotics are known as synbiotics. The benefits of pro- and prebiotics on the host include: normalization of the microbial balance in the gastrointestinal tract, increase of mineral bioavailability, reduction of cholesterol level in blood and prevention of gastrointestinal disorders. The aim of the work was to compare the apparent absorption and retention indexes in rats fed diets containing probiotic or synbiotic soft cheeses. As a probiotic, the strain Lactobacillus plantarum 14 was used, whereas as prebiotics inulin HPX and maltodextrin were used. For 10 days, the animals were fed diets consisting of 61-81% of soft cheese with probiotic (A diet), probiotic and 2,5% of inulin HPX (B diet) and probiotic and 2.5% of maltodextrin (C diet). On the basis of the magnesium concentration in the diets and the urine and faeces excreted during the last 5 days of the experiment, the apparent absorption (A) and retention (R) indexes (%, mg 5 days-1) were calculated. The apparent absorption indexes obtained did not differ statistically among the groups, although the highest value of apparent absorption (A%) was obtained in group B. The apparent retention indexes in group A were significantly higher (p < 0.05) compared to groups B and C. On the other hand, in B and C groups increased faecal mass was detected, but the inulin influence was stronger than that of maltodextrin. Although the short-term supplementation of rat diets with inulin HPX and maltodextrin did not increase magnesium absorption and retention, their use in probiotic products is reasonable because of the beneficial physiological effects.Jako produkty synbiotyczne są określane wyroby zawierające jednocześnie probiotyki i prebiotyki. Korzystny wpływ pro- i prebiotyków na organizm obejmuje m.in. normalizację składu mikroflory przewodu pokarmowego, zwiększanie biodostępności składników mineralnych, obniżanie poziomu cholesterolu we krwi oraz zapobieganie występowaniu zaburzeń jelitowych. Celem pracy było porównanie wpływu diety zawierającej probiotyczny i synbiotyczne serki twarogowe na absorpcję i retencję magnezu u szczurów. Zastosowanym szczepem probiotycznym był Lactobacillus plantarum 14, a prebiotykami inulina HPX oraz maltodekstryna średniosckukrzona. Zwierzętom przez 10 dni podawano diety, w skład których wchodził serek twarogowy, w ilości 61-81%, zawierający: probiotyk (dieta A), probiotyk i 2,5% inuliny HPX (dieta B) lub probiotyk i 2,5% maltodekstryny (dieta C). Na podstawie zawartości magnezu w diecie, kale i moczu wydalonego w czasie ostatnich 5 dni eksperymentu, wyznaczono współczynniki absorpcji (A) i retencji (R) pozornej (%, mg 5 dni-1). Uzyskane współczynniki absorpcji nie różniły się znacząco między grupami zwierząt, chociaż najwyższy (A%) odnotowano w grupie B, natomiast wartości współczynników retencji pozornej w grupie A były istotnie wyższe (p < 0,05) w porównaniu z grupami B i C. W grupach przyjmujących dietę synbiotyczną obserwowano zwiększenie masy kału w porównaniu z grupą kontrolną A, przy czym działanie inuliny HPX było silniejsze niż maltodekstryny. Chociaż krótkotrwała suplementacja diety szczurów inuliną HPX i maltodekstryną średnioscukrzoną nie przyczyniła się do wzrostu absorpcji i retencji magnezu, tostosowanie tych prebiotyków łącznie ze szczepem probiotycznym jest uzasadnione ze względu na korzystne efekty fizjologiczne

Badanie czynnikow warunkujacych spozycie pozywienia - preferencje pokarmowe

The preferences for three protein and six carbohydrate products were examined in young, growing, male Wistar rats. The selected products were successively excluded from the choices given to rats and the changes in preference were observed. The rats were shown to prefer carbohydrate products more than protein products. For the carbohydrate products, the intake of wheat flour and pearl barley was the highest, of corn flour and buckwheat groat the lowest. From the protein products, the rats selected most often soybean meal and the least Canola meal. The rats were able to regulate the intake regarding both the type and amount of food. The preferences for certain products changed depending on the choice offered for consumption. Over a short-term period of the experiment, no specific preferences for the vitamins supplied with corn starch were observed. The preferences for Canola meal and buckwheat groat increased after the rats had adapted to their consumption.Badaniom poddano białkowe i węglowodanowe produkty paszowe i spożywcze. W kolejnych etapach doświadczenia wytypowane produkty eliminowano obserwując zmianę preferencji na pozostałe produkty. Preferencje pokarmowe określono na młodych, rosnących szczurach szczepu Wistar, płci męskiej. Uzyskane wyniki badań dowodzą, że zwierzęta wykazywały wyższe preferencje w stosunku do produktów węglowodanowych niż produktów białkowych. Z produktów węglowodanowych najwyższe spożycie stwierdzono w przypadku mąki pszennej i kaszy jęczmiennej, zaś najniższe w przypadku mąki kukurydzianej i kaszy gryczanej. Spośród produktów białkowych szczury najchętniej wybierały śrutę sojową, natomiast w najmniejszej ilości spożywały śrutę rzepakową. Zwierzęta posiadały zdolność regulacji zarówno rodzaju, jak i ilości spożywanego pożywienia, a preferencje pokarmowe do określonych produktów zmieniały się, w zależności od zestawu pokarmów podawanych im do spożycia. Nie stwierdzono specyficznych preferencji szczurów do witamin dostarczonych z produktami. Preferencje pokarmowe zwierząt do niektórych produktów (śruta rzepakowa, kasza gryczana) wzrastały po okresie przyzwyczajenia do ich spożywania