Problem statement: Lactobacillus delbrueckii subsp. bulgaricus is a lactic bacteria mostly used in the production of yoghurt and it has an important probiotic activity that brings benefits to the human body. However, the gastrointestinal tract has aggressive conditions, such as the acid pH in the stomach and the bile in the duodenum, that reduce the viability of this bacteria. Approach: In order to evaluate the effect of the human gastrointestinal conditions on Lactobacillus delbrueckii's viability, a simulated in vitro gastrointestinal system was designed, which consisted of two reactors where stomach and human small intestine conditions were simulated. Results: Lactobacillus delbrueckii cells were treated in human gastric conditions simulated in vitro (gastric juice adjusted to pH 2, 37°C, 90 min and 50 rpm) and in intestinal conditions simulated in vitro (pancreatic juice adjusted to pH 6.8, 37°C, 150 min and 50 rpm) and in presence of a sample of food or beverages. A sample of typical Mexican food was added and at the end of the treatment 73% of the cells remained viable. This means 36.5 times more viability with respect to the cells treated under the same conditions in presence of a sample of milk with 8% starch. At the end of the treatment, the viability of cells treated in simulated in vitro gastrointestinal juices without sample of food or beverage (blank) was 1%. Conclusion: The results indicated that the in vitro simulated human gastrointestinal conditions were aggressive to the Lactobacillus delbrueckii's viability. To minimize this negative effect it is suggested that probiotics be consumed with some food because this could increase the probability that the bacteria reach the human colon in a large number and carry out their probiotic effect.
Currently, obtaining sustainable fuels, such as biodiesel and bioethanol, from cheap and renewable materials is a challenge. In recent years, a new approach being developed consists of producing, sugars from algae by photosynthesis. Sugar accumulation can be increased under osmotic stress (osmoregulation). The aim of this study is to show the pro-duction of sugars from algae, isolated from natural sources, and the effect of osmotic stress on fermentable sugars ac-cumulation. Strain isolation, production of sugars from each alga and the effect of osmotic stress on growth and sugar production are described. Twelve algal strains were isolated, showing growths between 0.6 and 1.8 g of biomass dry weight /L, all with production of intracellular and extracellular sugars. The strain identified as Chlorella sp. showed an increase in sugar production from 23.64 to 421 mg of sugars/g of biomass dry weight after 24 h of osmotic stress with 0.4 M NaCl. Sucrose and trehalose, both fermentable sugars, were the compatible osmolytes accumulated in response to the osmotic stress. The isolated strains are potential producers of fermentable sugars, using the photosynthetic pathway and osmotic stress
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