M.A. Murado

A method for bacteriocin quantification

M.L. CABO, M.A. MURADO, M.P. GONZÁLEZ and L. PASTORIZA.1999.Different aspects of the most commonly used assay methods in the study of bacteriocins were examined. The conditions under which extraction and incubation (including exposure time) take place were analysed, and several different formal models that are usually employed to calculate ID50 were compared. As an alternative designed to overcome the problems which characterize the response of micro‐organisms that are sensitive to bacteriocins, an operative procedure in a liquid medium and a modified re‐parameterized logistic equation is proposed. When applied to the inhibition of Leuconostoc mesenteroides by nisin, the model allows an optimal experimental procedure to be defined.

Effects of aeration and pH gradient on nisin production.: A mathematical model

A study on the effects of aeration and pH on nisin production by Lactococcus lactis showed significant increases as either aeration or pH drop gradient were risen. Nisin production at the maximum biomass point quadrupled when the oxygen saturation percentage increased from 50 to 100%. This suggests the association of this bioproduction with an oxidative metabolic pathway. A procedure based on successive re-alkalizations of the culture with feeding with glucose at regular intervals was proposed. It was shown that pH drop gradient (VpH) enhances nisin production, which increased approximately four-fold, and increases the efficiency of nutrient consumption. By using conventional equations of microbial kinetics, with the only additional assumption that VpH has some effect on the growth rate of the microorganism, a model that describes the results successfully is proposed. This model enables nisin to be typified as a primary metabolite, which tends to acquire secondary nature when the productive period of the culture is prolonged by imposing a stepwise-pH profile.

Chondroitin sulfate, hyaluronic acid and chitin/chitosan production using marine waste sources: characteristics, applications and eco-friendly processes: a review.

In the last decade, an increasing number of glycosaminoglycans (GAGs), chitin and chitosan applications have been reported. Their commercial demands have been extended to different markets, such as cosmetics, medicine, biotechnology, food and textiles. Marine wastes from fisheries and aquaculture are susceptible sources for polymers but optimized processes for their recovery and production must be developed to satisfy such necessities. In the present work, we have reviewed different alternatives reported in the literature to produce and purify chondroitin sulfate (CS), hyaluronic acid (HA) and chitin/chitosan (CH/CHs) with the aim of proposing environmentally friendly processes by combination of various microbial, chemical, enzymatic and membranes strategies and technologies.

Dose-response relationships: an overview, a generative model and its application to the verification of descriptive models

Abstract Taking as a starting point a set of simple quantitative hypotheses regarding the possible relationships between cell receptors and effector molecules, a statistical algorithm or generative model is developed that simulates different types of dose–response (DR) profiles and whose results are used in two ways, both subject to empirical verification. In the first of these, the suitability of several common descriptive models for the study of DR relationships is discussed, and changes are introduced that improve their suitability for this conceptual framework, generalise their application and lead to the systematisation of possible interactions between more than one effector, as well as between the effects of self-stimulating and self-depressor mechanisms. Secondly, the generative model suggests the existence of some unexpected profiles and their possible explanations. Both the profiles and the hypotheses appear to be supported by experimental evidence.

Amylase production by solid state culture of Aspergillus oryzae on polyurethane foams. Some mechanistic approaches from an empirical model

Abstract Using systems formed by particles of polyurethane foam of different densities soaked in an amylaceous effluent, the production of amylases by Aspergillus oryzae in solid state culture was studied by a complete factorial plan with four variables — support density, particle diameter, volume of liquid phase and substrate concentration. The empirical model obtained is consistent and allows a simple control of the response, superior in several respects to that of the corresponding submerged cultures. Moreover, it enables a mechanistic approach to the behaviour of the system, whose principal kinetic characteristics can be interpreted in terms of intra- and interparticular diffusional effects, which have a determining influence on basic state variables, such as water activity and gas transfer.

Characterization of microbial biomasses and amylolytic preparations obtained from mussel processing waste treatment

This work describes a treatment of glycogen-rich wastes from industrial mussel processing, involving the production of a protein fraction and a medium suitable for the culture of amylolytic microfungi. A strain of Aspergillus oryzae was chosen which allows the simultaneous production of single cell protein and a highly stable amylolytic preparation. The characteristics of the biomass obtained (proportion and in vitro digestibility of the proteins, levels of essential amino acids and nucleic acids, types of fatty acids present) were shown to be suitable, in principle, for animal feeds. The amylolytic preparation, obtained by ultrafiltration (with cut-off at 30 kD) of the cell-free medium, was very similar to commercial α-amylase preparations, containing mainly α-amylase, together with a small proportion of glucoamylase.

Optimization of nutrient concentration for citric acid production by solid-state culture of Aspergillus niger on polyurethane foams

Abstract Citric acid production from mussel processing effluents by Aspergillus niger in solid-state culture was studied using polyurethane foam particles soaked with the culture medium. Conditions were used that allowed comparison of the results with those obtained before in submerged culture and the attribution of the differences to the characteristics of solid-state culture. A screening of several strains gave different results than in submerged culture and a reduction in the incubation time. The joint effect of nitrogen and phosphorus initial concentrations was examined by means of orthogonal factorial designs in five selected strains. The results showed that different requirements of N and P for each individual strain were needed. Optimization was done using different experimental strategies for two selected strains. Following either the direction of the linear approximation gradient of the first-order empirical model obtained or with a new rotatable factorial design, an optimum value could be obtained. In comparison with previous results in submerged culture, the strains with high requirements of N and P seemed to be disfavored in solid-state culture. The ones with low requirements were favored and showed a bigger tolerance to a surplus of both nutrients.

β-Carotene Assay Revisited. Application To Characterize and Quantify Antioxidant and Prooxidant Activities in a Microplate

The β-carotene bleaching assay, a common method for evaluating antioxidant activity, has been widely criticized due to its low reproducibility, problematic quantification, complex reagent preparation, and interference of different factors (temperature, pH, solvents, and metals). In this work we have examined the effects of these factors and developed a highly reproducible procedure for microplate assay, evaluated the critical points of the method, and proposed a kinetic model for quantifying both antioxidant and prooxidant activities. The application of these tools produced very consistent results, which provide robust and meaningful criteria to compare in detail the characteristics of several well-known commercial antioxidants, as well as several predictable prooxidants, and can be easily applied to natural extracts, food samples, and many other type of compounds. As an example, we have tested a set of commercial antioxidants and some typical lipophilic prooxidants. The activity of the tested antioxidants decreased in the following order: ethoxyquin ≫ α-tocopherol > butylhydroxyanisole > butylhydroxytoluene ≫ propyl gallate. On the other hand, hemoglobin and Fe(2+), Fe(3+), Co(2+), and Cu(2+) showed a strong prooxidant effect, and the activity was null in Cd(2+), Ni(2+), and Sr(2+), slightly antioxidant in Mg(2+), and strongly antioxidant in Zn(2+) and Mn(2+).

Diauxic production of glucose oxidase by Aspergillus niger in submerged culture: A dynamic model

On studying the production of glucose oxidase (GOD) by Aspergillus niger, we find that both growth and production are diauxic processes, with logistic and linear phases. The gluconic acid that is produced from glucose by means of enzyme action can therefore be considered as a useful source of carbon for growth, and does not interfere with the biosynthesis of GOD in spite of being a product of its activity. From a kinetic viewpoint, the enzyme is a primary metabolite, but this can only be proved by including the Luedeking and Piret equation in a dynamic model that takes into account the effects of hydrogen peroxide on GOD, as well as those of the catalase, which is also produced by the microorganism, on the hydrogen peroxide.

INTERACTIVE EFFECTS OF SALINITY AND TEMPERATURE ON PLANOZYGOTE AND CYST FORMATION OF ALEXANDRIUM MINUTUM (DINOPHYCEAE) IN CULTURE(1).

The factors regulating dinoflagellate life‐cycle transitions are poorly understood. However, their identification is essential to unravel the causes promoting the outbreaks of harmful algal blooms (HABs) because these blooms are often associated with the formation and germination of sexual cysts. Nevertheless, there is a lack of knowledge on the factors regulating planozygote‐cyst transitions in dinoflagellates due to the difficulties of differentiating planozygotes from vegetative stages. In the present study, two different approaches were used to clarify the relevance of environmental factors on planozygote and cyst formation of the toxic dinoflagellate Alexandrium minutum Halim. First, the effects of changes in initial phosphate (P) and nitrate (N) concentrations in the medium on the percentage of planozygotes formed were examined using flow cytometry. Second, two factorial designs were used to determine how salinity (S), temperature (T), and the density of the initial cell inoculum (I) affect planozygote and resting‐cyst formation. These experiments led to the following conclusions: