Simultaneous effects of pH and substrate concentration on hydrogen production by acidogenic fermentation / Efectos simultáneos del pH y la concentración de sustrato en la producción de hidrógeno mediante fermentación acidogénica

The present research examined the effects of initial substrate concentration and pH on the yield and productivity of hydrogen production by acidogenic fermentation. Assays were carried out at three different initial pH levels (5.5, 6.5 and 7.5) and three initial substrate concentrations (3, 5 and 10 g COD/L). Glucose was used as carbon source and the experiments were conducted at 37°C in batch tests, after a thermal pretreatment to eliminate methanogenic microorganisms. Conversions of glucose into hydrogen were between 16.75 and 27.25 percent of theoretical maximum, and high values of hydrogen productivity were obtained. An optimum value for the yield of glucose between initial pH of 6.3 and 3.7 g COD/L and productivity of the 5.95 H2/gVSS h and initial pH of 6.7 and 10 g COD/L were obtained from the response surface.

Efecto de la caseína en la absorción de d-xilosa medida mediante la prueba de H2 espirado / Effect of casein on d-xylose absorption measured by expired H2 test

Different experimental studies suggest that the presence of food in the alimentary tract, promote small intestinal absorption. The mechanism involved are not completely understood and might be related to motility changes or to humoral factors. Since studies have shown a decrease of small bowel motility after casein administration, the aim was to analyze the effect of this protein on small intestinal absorption and orocecal transit time. The hydrogen breath test was used to estimate d-xylose absorption. H2 production is dependent on the amount of this carbohydrate reaching the colon and therefore inversely proportional to d-xylose absorption. Six normal volunteers ingested 25 g d-xylose and 25 g de-xyllose + 30 g casein, and alveolar breath samples were obtained at 15 min intervals. Results: by adding casein to d-xylose solution a statistically significant decrease of maximal H2 concentration was observed from a mean of 40ñ11 ppm to a mean of 26ñ8 ppm. Similarly the area under the curve (which reflects the amount of xylose that was not absorbed) was also significantly decreased from a mean of 3281ñ1399 ppm to mean of 1394ñ700 ppm of H2. The orocecal transit time was significantly prolonged from 85.5ñ40 min to 112ñ38 min. Our results suggest that casein increased d-xylose absorption in normal subjects and that this effect might be related to a slower transit time

Efecto de un extracto seco de boldo sobre el tránsito intestinal oro-cecal en voluntarios sanos / Effect of a dry boldo extract on oro cecal intestinal transit time in healthy volunteers

Background: Boldo (peumus boldus Molina) is a widely used medicinal plant. However, its physiological effects are not well known. Recent studies in animals showed that certain components of boldo relax smooth muscle and prolong intestinal transit. Aim: to assess the effects of a dry boldo extract on oro cecal transit time in normal humans. Subjects and methods: twelve volunteers received 2.5 g of a dry boldo extract or a placebo (glucose) during 2 successive periods of 4 days. On the fourth day, 20 g of lactulose were administered and breath hydrogen was collected every 15 min. Oro cecal transit time was defined as the time in which breath hydrogen increased by 20 ppm over the fasting level. Results: oro cecal transit time was larger after dry boldo extract administration, compared to placebo (112.5ñ15.4 and 87ñ11.8 min respectively, paired t p<0.05). Conclusions: dry boldo extract prolongs oro cecal transit time, a possible explanation for its medicinal use