RESUMO

We developed a mathematical model to simulate dynamics associated with the proliferation of Geobacter and ultimately optimize cellular operation by analyzing the interaction of its components. The model comprises two segments: an initial part comprising a logistic form and a subsequent segment that incorporates acetate oxidation as a saturation term for the microbial nutrient medium. Given that four parameters can be obtained by minimizing the square root of the mean square error between experimental Geobacter growth and the mathematical model, the model underscores the importance of incorporating nonlinear terms. The determined parameter values closely align with experimental data, providing insights into the mechanisms that govern Geobacter proliferation. Furthermore, the model has been transformed into a scaleless equation with only two parameters to simplify the exploration of qualitative properties. This allowed us to conduct stability analysis of the fixed point and construct a co-dimension two bifurcation diagram.

Assuntos

RESUMO

Resumen: Los cormos de malanga son tallos subterráneos con alto valor nutrimental por su contenido de carbohidratos y proteínas, además de ser altamente digestivos. El almidón que se extrae de ellos puede ser utilizado en la encapsulación de microorganismos probióticos, de gran importancia para la salud. El objetivo de este trabajo fue desarrollar un suplemento alimenticio con características funcionales, usando bacterias ácido lácticas (BAL) (Lactobacilos casei), encapsuladas en almidón de malanga (Xanthosoma sagittifolium). El suplemento se realizó mezclando 150 mL de pulpa de fruta cocida (mango o manzana) con 400 mL de suero de leche (pH de 6.0), a 45 ± 1 °C, hasta conseguir la consistencia deseada (449.9 mPas/s a una temperatura de 25 ºC). Posteriormente, se adicionaron 1 % o 2 % de almidón de malanga (p/v) y 10 mL de cultivo probiótico por cada 100 mL de mezcla. Se deshidrató a 80 ºC y 150 ºC con flujo de aire de 20 mL/min para manzana y 8 mL/min para mango mediante secado por aspersión. El rendimiento fue de 12 %, con una viabilidad de las BAL en el suplemento deshidratado a los 3 meses de almacenamiento superior a 1 x 108 UFC/g. La ausencia de bacterias coliformes, así como de salmonella y shigella, indican que los suplementos son inocuos y aptos para consumo. La composición nutrimental del suplemento de manzana obtenido fue2.23 % de fibra, 5.93 % de grasa, 4.95 % de proteína y un 79 % de hidratos de carbono; el suplemento de mango, el contenido fue 0.59 % de fibra, 7.6 % de grasa, 4.2 % de proteína y 80.20 % de hidratos de carbono. El almidón de malanga permitió la microencapsulación de las BAL y mantener su viabilidad durante el almacenamiento de los suplementos alimenticios desarrollados con base en suero de leche y fruta.

Abstract: Malanga corms are an underground stem with a high nutritional value as it contains carbohydrates and proteins, in addition to being highly digestive; The starch extracted from them can be used in the encapsulation of probiotic microorganisms, which are of great importance for human health. The objective of this work was to develop a food supplement with functional characteristics, added with lactic acid bacteria (Lactobacillus casei) (LAB), using malanga (Xanthosoma sagittifolium) starch. The supplement was obtained by mixing 150 mL of cooked fruit pulp (mango or apple) with 400 mL of sweet whey (pH of 6.0), at a temperature of 45 ± 1 °C until the desired consistency (449.9 mPas/s at a temperature of 25 °C) was achieved. Subsequently, 1 % or 2 % of malanga starch (p/v) and 10 mL of probiotic cultures were added per each 100 mL of mixture. it was then dehydrated at 80 ºC and 150 °C with an air flow of 20 mL/min for apple and 8 mL/min for mango by spray drying. The yield was 12 %, with viability of LAB in the dehydrated supplement at 3 months of storage higher than 1 x 108 CFU/g. The absence of coliform bacteria, as well as Salmonella and Shigella, indicate that the supplements are safe and suitable for consumption. The nutritional composition of the apple supplement was 2.23 % fiber, 5.93 % fat, 4.95 % protein and 79 % carbohydrates; the mango supplement content was 0.59 % fiber, 7.6 % fat, 4.2 % protein and 80.20 % carbohydrates. The malanga starch allowed the LAB microencapsulation and the maintenance of their viability during the storage of sweet whey and fruit-based food supplements.

RESUMO

Magnesium oxide nanoparticles (MgO NPs) were obtained by the calcination of precursor microparticles (PM) synthesized by a novel triethylamine-based precipitation method. Scanning electron microscopy (SEM) revealed a mean size of 120 nm for the MgO NPs. The results of the characterizations for MgO NPs support the suggestion that our material has the capacity to attack, and have an antibacterial effect against, Gram-negative and Gram-positive bacteria strains. The ability of the MgO NPs to produce reactive oxygen species (ROS), such as superoxide anion radicals (O2•-) or hydrogen peroxide (H2O2), was demonstrated by the corresponding quantitative assays. The MgO antibacterial activity was evaluated against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria, with minimum inhibitory concentrations (MICs) of 250 and 500 ppm on the microdilution assays, respectively. Structural changes in the bacteria, such as membrane collapse; surface changes, such as vesicular formation; and changes in the longitudinal and horizontal sizes, as well as the circumference, were observed using atomic force microscopy (AFM). The lipidic peroxidation of the bacterial membranes was quantified, and finally, a bactericidal mechanism for the MgO NPs was also proposed.