D. Cantero

Cereal-based fermented foods and beverages

Cereal grains constitute a major source of dietary nutrients all over the world. Although cereals are deficient in some basic components (e.g. essential aminoacids), fermentation may be the most simple and economical way of improving their nutritional value, sensory properties, and functional qualities. This review focuses first on some of the indigenous fermented foods and beverages produced world-wide that have not received the scientific attention they deserve in the last decades. Products produced from different cereal substrates (sometimes mixed with other pulses) fermented by lactic acid bacteria, yeast and/or fungi are included. Finally, newly developed cereal-based foods with enhanced health properties will also be reviewed.

Formation of calcium alginate gel capsules: influence of sodium alginate and CaCl2 concentration on gelation kinetics.

The formation kinetics of calcium alginate gel capsules is studied. An increase in the concentration of alginate gives rise to a reduction in membrane thickness, while an increase in the concentration of calcium chloride leads to the formation of a thicker film. Experimental data are adjusted to the binomial diffusion equation.

Immobilization of glucose oxidase within calcium alginate gel capsules

Abstract Glucose oxidase (GOD) was encapsulated within calcium alginate gel capsules. The effects of gelation conditions on capsule characteristics such as thickness, percentage of enzyme leakage and encapsulation efficiency were studied and the optimal conditions for GOD encapsulation obtained. Oxidation of glucose to gluconic acid followed Michaelis–Menten kinetics.

Glucose oxidase release from calcium alginate gel capsules

Diffusion of glucose oxidase within calcium alginate gel capsules has been assayed and the experimental data fitted to a simple semi-empirical power equation, which is used to analyse the solute release from polymeric devices. It was found that an increase in the concentration of sodium alginate and calcium chloride gives rise to a reduction in the enzyme leakage. This was verified when glucose oxidase (GOD) diffusion percentages were compared in capsules with thicknesses of the same order of magnitude but obtained under different experimental conditions. So, the use of sodium alginate and calcium chloride solutions of concentrations 0.5% w/v and 2.6% w/v, respectively, lead to a diffusion percentage of 25 +/- 2. This percentage was reduced to 8 +/- 3 when sodium alginate and calcium chloride concentrations were fixed at 1% w/v and 4% w/v, respectively, even though the thicknesses of the capsules were of the same order of magnitude.

Removal of hydrogen sulfide by immobilized Thiobacillus thioparus in a biotrickling filter packed with polyurethane foam

In the work described here, a biotrickling filter with Thiobacillus thioparus (ATCC 23645) immobilized on polyurethane foam is proposed for the removal of hydrogen sulfide contained in air. The effect of surface velocity of the recirculation medium (5.9-1.2 m/h), sulfate concentration inhibition (3.0-10.7 g/L), pH (6.0-8.2), empty bed residence time (EBRT) (150-11 s) for constant loads of 11.5 and 2.9 g S/m(3)/h, and pressure drop of the system were investigated. The total amount of biomass immobilized on the carrier was 8.2+/-1.3x10(10) cells/g. The optimal values of the operating variables were: pH between 7.0 and 7.5, surface velocity of 5.9 m/h and sulfate concentration below 5 g/L. The critical EC value was 14.9 g S/m(3)/h (removal efficiency of 99.8%) and the EC(max) was 55.0 g S/m(3)/h (removal efficiency of 79.8%) for an EBRT of 150 s. For loads of 2.89+/-0.05 and 11.5+/-0.1 g S/m(3)/h, the removal efficiency was higher than 99% for an EBRT over 90 s.

Optimization of immobilization conditions for vinegar production. Siran, wood chips and polyurethane foam as carriers for Acetobacter aceti

Abstract A complete experimental design has been developed to study the properties of three different solid carriers (Siran, wood chips and polyurethane foam) in the immobilization of acetic acid bacteria. Temperature-controlled reactors of 450-ml volume were employed to compare a standard immobilization procedure consisting of consecutive discontinuous acetic acid fermentations in the presence of the carrier. On reaching the final saturation condition, the different immobilized carriers were removed and introduced into identical sterilized reactors. These were then submitted to several semi-continuous fermentation cycles with the aim of characterising and comparing their acetification properties. Immobilization and acetification data obtained in this study have been evaluated in order to determine the best carrier material on the basis of several technical criteria. Polyurethane foam was the most successful because it allows a huge number of immobilized cells in the shortest time and leads to the highest acetification rate of the three assayed carriers.

Utilisation of whole wheat flour for the production of extracellular pectinases by some fungal strains

The possibility of producing pectinases by Rhizopus stolonifer and Aspergillus awamori, using cereal raw materials as substrate, was investigated. The whole wheat flour acted as a good nutrient source for the cultivation of the microorganisms and exo- and endo-polygalacturonases (PG) were produced in submerged culture. In this respect, it was possible to obtain polygalacturonase activities at an acceptable yield, in comparison with a typical defined medium described in the literature for pectinase production. The synthesis of both enzymes occurred in both strains in the absence of pectin, demonstrating the constitutive nature of these enzymes; nevertheless, production was increased by the addition of a small amount of pectin to the flour.

Biofiltration of reduced sulphur compounds and community analysis of sulphur-oxidizing bacteria

The present work aims to use a two-stage biotrickling filters for simultaneous treatment of hydrogen sulphide (H(2)S), methyl mercaptan (MM), dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). The first biofilter was inoculated with Acidithiobacillus thiooxidans (BAT) and the second one with Thiobacillus thioparus (BTT). For separate feeds of reduced sulphur compounds (RSC), the elimination capacity (EC) order was DMDS>DMS>MM. The EC values were 9.8 g(MM-S)/m(3)/h (BTT; 78% removal efficiency (RE); empty bed residence time (EBRT) 58 s), 36 g(DMDS-S)/m(3)/h (BTT; 94.4% RE; EBRT 76 s) and 57.5 g(H2S-S)/m(3)/h (BAT; 92% RE; EBRT 59 s). For the simultaneous removal of RSC in BTT, an increase in the H(2)S concentration from 23 to 293 ppmv (EBRT of 59 s) inhibited the RE of DMS (97-84% RE), DMDS (86-76% RE) and MM (83-67% RE). In the two-stage biofiltration, the RE did not decrease on increasing the H(2)S concentration from 75 to 432 ppmv.

Biogas biodesulfurization in an anoxic biotrickling filter packed with open-pore polyurethane foam.

Biogas biodesulfurization by an anoxic biotrickling filter packed with open pore polyurethane foam at the laboratory scale (packed volume 2.4L) has been studied. The biotrickling system was operated for 620 days with biogas supplied continuously and two nitrate feeding regimes were tested (manual and programmed). Biomass immobilization was carried out under the manual nitrate feeding regime and a study was then carried out on the effects on removal efficiency of the following parameters: nitrate source, H2S inlet load, nitrate concentration, sulfate accumulation, temperature, pH and trickling liquid velocity. The effect of increased H2S inlet load was studied under the programmed nitrate feeding regime. The results show that a removal efficiency of 99% can be obtained when working under the following conditions: inlet loads below 130gSm(-3)h(-1), a programmed nitrate feeding system, temperature of 30°C, sulfate concentration below 33gL(-1), a pH between 7.3 and 7.5, and a trickling liquid velocity higher than 4.6mh(-1).

Modelling the kinetics of growth of Acetobacter aceti in discontinuous culture: influence of the temperature of operation

Acetic acid fermentation is the biochemical process by which, under strict conditions of aerobiosis, Acetobacter aceti oxidises the ethanol contained in alcoholic substrates into acetic acid. This paper studies the effect of temperature on the specific growth rate of the microorganisms (μC), in particular, the mathematical modelling of this process, with the aim of developing previous studies of the mathematical relationships between μC of A. aceti and the concentrations of substrate (ethanol), product (acetic acid) and dissolved oxygen. Until now this relationship has not been widely studied, and only a few studies have looked at the influence of temperature on growth kinetics of this bacteria. We have developed an extensive experimental system, to determine precisely the influence of temperature on the maximum specific growth rate.