Volatile Compounds in Tofu Obtained by Soy Milk Fermentation with Lactobacillus plantarum BAL-03-ITTG and Lactobacillus fermentum BAL-21-ITTG.

Tofu is one of the main foods made with soybeans. The aim of this work was to evaluate the effect of L. plantarum and L. fermentum on the volatile compounds and sensorial profile of fermented tofu during ripening. The soy milk was fermented separately with two native strains (L. plantarum or L. fermentum) until reaching a pH of 5.5, and the fermented tofu was obtained. The tofu obtained by acidification with lactic acid was used as a control and was characterized by microbial survival (L. plantarum, L. fermentum, and P. freudenreichii) for 0, 20, and 40 days of storage at 15 °C. Moreover, the lactic and acetic acid content was determined by high-performance liquid chromatography (HPLC), and the volatile compounds were evaluated by gas. Chromatography-mass spectrometry (GC-MS). The results were analyzed by an ANOVA test (P < 0.05). After storage, the lactic acid bacteria (LAB) survived in the fermented tofu at a concentration higher than 8.0 log CFU/g after 40 days of storage. The shelf life of fermented tofu obtained by acidification was fewer than 20 days because of the presence of fungi and yeasts. The hexanal content was reduced by approximately 96% (P < 0.05) in the tofu obtained by fermentation compared with the control. This process for fermented tofu production employing two native strains could be used for industrial purposes.

Effect of linear and branched fructans on growth and probiotic characteristics of seven Lactobacillus spp. isolated from an autochthonous beverage from Chiapas, Mexico.

The effect that the fructans of Cichorium intybus and Agave salmiana have on health, as well as on the growth of some Lactobacillus species, has been demonstrated. The aim of this work was to evaluate the effect of linear and branched fructans on the growth of seven strains and some probiotic characteristics. The molecular identification of seven strains was performed. Moreover, the growth, resistance to antibiotics and simulated gastrointestinal conditions were also evaluated when these microorganisms were grown in a culture medium containing agave and chicory fructans. The strains were identified as Lactiplantibacillus plantarum, Lactiplantibacillus pentosus, Lactiplantibacillus fabifermentans and Lactiplantibacillus paraplantarum. The results suggest that the seven Lactobacillus strains were able to grow using agave (branched) and chicory (linear) fructans. The linear and branched fructans statistically influenced the kinetic parameters. The specific growth rate varied between 0.270 and 0.573 h-1 and the generation time between 1.21 and 2.45 h for all strains and culture media. All strains showed a growth of 9 Log CFU/mL in all the culture media. Production of lactic, acetic, propionic, butyric, formic and succinic acid was influenced by linear and branched fructans (p < 0.05). All the strains survived simulated gastrointestinal conditions greater than 83%. The resistance of Lactobacillus against ciprofloxacin and rifaximin was significantly affected by linear and branched fructans, but survival to gastrointestinal conditions was not affected by the type of substrate. These results highlight the use of the seven strains, which have probiotic potential; therefore, these could be applied in several biotechnological products.

Computational Study of Thermal Comfort and Reduction of CO2 Levels inside a Classroom.

Due to the current COVID-19 pandemic, guaranteeing thermal comfort and low CO2 levels in classrooms through efficient ventilation has become vitally important. This study presents three-dimensional simulations based on computational fluid dynamics of airflow inside an air-conditioned classroom located in Veracruz, Mexico. The analysis included various positions of an air extractor, Reynolds numbers up to 3.5 × 104, four different concentrations of pollutant sources, and three different times of the day. The simulations produced velocity, air temperature, and CO2 concentrations fields, and we calculated average air temperatures, average CO2 concentrations, and overall ventilation effectiveness. Our results revealed an optimal extractor position and Reynolds number conducive to thermal comfort and low CO2 levels due to an adequate ventilation configuration. At high pollutant concentrations, it is necessary to reduce the number of students in the classroom to achieve safe CO2 levels.

Numerical Study of Nanofluid Irreversibilities in a Heat Exchanger Used with an Aqueous Medium.

Heat exchangers play an important role in different industrial processes; therefore, it is important to characterize these devices to improve their efficiency by guaranteeing the efficient use of energy. In this study, we carry out a numerical analysis of flow dynamics, heat transfer, and entropy generation inside a heat exchanger; an aqueous medium used for oil extraction flows through the exchanger. Hot water flows on the shell side; nanoparticles have been added to the water in order to improve heat transfer toward the cold aqueous medium flowing on the tube side. The aqueous medium must reach a certain temperature in order to obtain its oil extraction properties. The analysis is performed for different Richardson numbers (Ri = 0.1-10), nanofluid volume fractions (φ = 0.00-0.06), and heat exchanger heights (H = 0.6-1.0). Results are presented in terms of Nusselt number, total entropy generation, Bejan number, and performance evaluation criterion. Results showed that heat exchanger performance increases with the increase in Ri when Ri > 1 and when reducing H.