Synthesis and characterization of functional calcium-phosphate-chitosan adsorbents for fluoride removal from water.

Functional calcium-phosphate-chitosan adsorbents for fluoride (F-) removal from water with different proportions of calcium (0.7 or 1.4 % w/v) were synthesized by: i) ionotropic gelation technique followed by drying in a convection oven (IGA) or freeze drying (FDA); ii) freeze-gelation followed by drying in a convection oven (FGA). Adsorbents were analyzed by SEM-EDX and FTIR- ATR. F- removal percentages higher than 45 % were obtained with calcium-phosphate-chitosan adsorbents for an initial F- concentration of 9.6 mg L-1. Optimal conditions for F- removal were attained, using calcium-phosphate- chitosan adsorbents synthesized by ionotropic gelation with 0.7 % of Ca (IGA0.7). Under these conditions, initial F- concentration of 5 mg L-1, was reduced below the maximum limit of 1.5 mg L-1 established by WHO. Regeneration of IGA0.7 was achieved in acid media. The performance of IGA0.7 was slightly reduced in the presence of coexisting anions (nitrate, carbonate, arsenate). Adsorption kinetics was represented satisfactorily by the pseudo-second order equation; Langmuir isotherm provided the best fit to the equilibrium data and IGA0.7 exhibited a maximum F- adsorption capacity qL = 132.25 mg g-1. IGA0.7 particles were characterized by thermogravimetry coupled to FTIR, XRD, XPS and SEM-EDX. The calcium-phosphate-chitosan adsorbents constitute a suitable and emerging material for water defluorination.

Biological removal of hexavalent chromium: evaluation of the metabolic activity of native and Cr(VI)-acclimated activated sludge using a respirometric method.

Hexavalent chromium becomes in one of the tops internationally concern environmental issues due to its wide usage in several industrial activities. There are two stable oxidation states of chromium in the environment which differ significantly on its toxicity; Cr(III) has lower solubility, mobility and lesser biological toxicity in comparison with Cr(VI). While Cr(VI) is a well-known carcinogen, Cr(III) is an essential dietary element. For this reason, most technologies focus attention on the reduction of Cr(VI) to Cr(III). On this context, the ability of microorganisms to reduce Cr(VI) to Cr(III) has gained attention. The objectives of the present work were to analyze the effect of Cr(VI) on the activated sludge community in a continuous reactor, and to evaluate the differences on the metabolic activity of native (NAS) and Cr(VI)-acclimated activated sludge (CrAAS) using a respirometric method. Results showed that the activated sludge community had the capability to acclimate to the presence of Cr(VI). On the other hand, the increase of the initial Cr(VI) concentration from 0 to 100 mgCr/L leads to a decrease in the specific exogenous respiration rate (qEx ) values, but this reduction was more noticeably in the case of NAS in comparison with CrAAS. The respirometric curves were well described by the proposed mathematical model. It was concluded that the CrAAS tolerated a Cr(VI) concentration about one order of magnitude higher than NAS, which was positively reflected in the respiration rate first-order decay constant (kd ), the specific maximum exogenous respiration rate (qExm ), and the observed oxidation coefficient (YO/S ) values.

Interdependence between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge in semi-continuous reactors.

The objective of the present work was to analyze the interrelationship between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge (AS) in semi-continuous reactors (SCRs). AS were obtained from three SCRs fed with glucose, acetate or peptone. AS from these reactors were used as inocula for three SCRs that were fed with each biogenic substrate, and for three SCRs that were fed with the biogenic substrate and BPA. In all cases, dissolved organic carbon (DOC), BPA, total suspended solids (TSS) and respirometric measurements were performed. Although BPA could be removed in the presence of all the tested substrates, AS grown on acetate exhibited the longest acclimation to BPA. Reactors fed with peptone attained the lowest TSS concentration; however, these AS had the highest specific BPA degradation rate. Specific DOC removal rates and respirometric measurements demonstrated that the presence of BPA had a negligible effect on the removal of the tested substrates. A mathematical model was developed to represent the evolution of TSS and DOC in the SCRs as a function of the operation cycle. Results suggest that the main effect of BPA on AS was to increase the generation of microbial soluble products. This work helps to understand the relationship between the biodegradation of BPA and readily biodegradable substrates.

Monitoring the biodegradability of bisphenol A and its metabolic intermediates by manometric respirometry tests.

As a result of its wide usage in the production of polycarbonate plastics and epoxy resins, bisphenol A (BPA) is commonly detected in wastewaters. Recently, BPA became a major concern because its adverse effects as an endocrine disruptor. In this work, the biodegradation kinetics of BPA and its metabolic intermediates 4-hydroxyacetophenone (4HAP), 4-hydroxybenzaldehyde (4HB) and 4-hydroxybenzoic acid (4HBA) by BPA-acclimated activated sludge was studied using manometric respirometry (BOD) tests. For all the tested compounds, BOD curves exhibited two phases. In the first one, a fast increase of the oxygen consumption (OC) due to the active oxidation of the substrate was obtained. Then, when the substrate was exhausted, the endogenous respiration produced a slower increase of OC. A standard Monod-model with biomass growth was used to represent the OC profiles as a function of time. For all the tested compounds, a good agreement between the proposed model and the experimental data was obtained. According to their biodegradation rates, the tested compounds can be ordered as follows: BPA < 4HAP â‰ª 4HB < 4HBA. Because the oxidation rate of BPA by BPA-acclimated activated sludge limits the rate of the whole biodegradation pathway, the accumulation of metabolic intermediates 4HAP, 4HB, and 4HBA would be negligible. To calculate the dissolved oxygen (DO) concentration (C) during the BOD tests, the oxygen transfer coefficient (kLa) of the BOD bottles was obtained using the sulfite method. Finally, a simple procedure to calculate the minimum DO concentration (Cmin) based on BOD data was developed. Calculation results demonstrated that under the tested conditions, C values were high enough as not to be the limiting substrate for the microbial growth.

Utilization of fluorescence spectroscopy as a novel approach to evaluate the oxidative stability in beef retail displayed.

Beef samples from grazing steers finished with different seed-supplemented diets were vacuum packaged for 3, 14 and 56days (VC) and subsequently exposed to aerobic conditions (AE) for 0 and 5days. Different fluorescent compounds of interest in the oxidation process were detected in meat, namely tryptophan residues, Schiff bases and porphyrins. Tryptophan intensity fluorescence increased with 14days of VC; while Schiff bases intensity increased (P<0.05) in beef samples stored under VC-56 and in all samples after AE-5days. Porphyrins increased (P<0.05) gradually with the extension of vacuum storage time, but were degraded in beef with long vacuum storage and 5days of AE. Higher levels of porphyrins in beef under VC were correlated (P<0.05) with lower redness and higher TBARS after AE-5. This study revealed the potential of fluorescence signals to detect oxidative changes in beef under different storage conditions using a fast and nondestructive method such as fluorescence spectroscopy.

Antioxidant status, lipid and color stability of aged beef from grazing steers supplemented with corn grain and increasing levels of flaxseed.

Angus steers were grazed on unsupplemented pasture (CNTRL), pasture supplemented with 0.7% BW cracked corn (FLAX-0), FLAX-0 with 0.125% and 0.250% BW of whole flaxseed (FLAX-1 and FLAX-2). Six steers were grazed per treatment for 70 days, with start and finish weights of 458 and 508 kg. At 24 h post slaughter, longissimus thoracis were harvested, and steaks assigned to treatments of postmortem aging time under vacuum (PM; 3, 14 and 56 days) with or without five days of aerobic exposure (AE). Meat antioxidant status was higher (P<0.05) when feeding CNTRL and FLAX-1 than FLAX-0 and FLAX-2. Under AE, lipid oxidation was highest for FLAX-2 (P<0.05), and lowest for FLAX-1. Greatest TBARs and lowest antioxidant capacity and redness values were obtained with AE and the longer PM (P<0.05). Beef oxidative stability through AE improved by adding a low flaxseed level to supplemented corn grain, but deteriorated by adding a high flaxseed level or by extending PM.

Simultaneous biodegradation of bisphenol A and a biogenic substrate in semi-continuous activated sludge reactors.

In this work, the simultaneous degradation of BPA and cheese whey (CW) in semi-continuous activated sludge reactors was studied. The acclimation process and microbial growth on BPA, CW and BPA + CW were analyzed. In addition, the effect of increasing CW concentration on the BPA degradation by acclimated activated sludge was also studied. In order to reduce the factors involved in the analysis of the simultaneous degradation of BPA and CW, the effect of bisphenol A (BPA) on activated sludge not previously exposed to BPA (native activated sludge) was studied. Results demonstrate that BPA concentrations lower than 40 mg l(-1) had a negligible effect on the growth of native activated sludge. In the semi-continuous reactors, the presence of CW increased the acclimation time to 40 mg l(-1) of BPA. Once the capability of degrading BPA was acquired, the removal of BPA was not affected by the presence of CW. Increasing the CW concentration did not affect the removal of BPA by the acclimated activated sludge. Additionally, the CW consumption was not modified by the presence of BPA. Kinetic and stoichiometric coefficients reported in the present work can be useful in developing mathematical models to describe the simultaneous aerobic biodegradation of a biogenic substrate, such as CW, and BPA by activated sludge.

Biological Cr(VI) removal coupled with biomass growth, biomass decay, and multiple substrate limitation.

In this work, a mathematical model for the biological reduction of Cr(VI), carbon and nitrogen sources consumption, and biomass growth under fully aerobic conditions was developed. The model comprises three types of aerobic heterotrophic cells (non-growing cells, growing cells with chromate reductase activity, and growing cells that have lost the chromate reductase activity), and five soluble compounds (organic substrate, ammonia nitrogen, non-metabolizable soluble products, dissolved oxygen, and hexavalent chromium). Two processes are considered responsible for the reduction of Cr(VI). The first one is the reduction of Cr(VI) coupled with growth, the second process is coupled with the endogenous decay of the biomass. The model was calibrated using the results obtained in batch cultures in the absence of carbon and nitrogen sources, using different initial Cr(VI) concentrations (0-100 mgCr L(-1)), two carbon sources (cheese whey and lactose), and different initial nitrogen to carbon ratio (0-50 mgN gCOD(-1)). The calibrated model was used to calculate steady-state values of TSS, soluble COD, TAN and Cr(VI) in continuous systems, obtaining a good agreement with the experimental data. The model also accurately predicted the transient concentration of Cr(VI) as a function of time in response to step changes of the inlet Cr(VI) concentration in continuous systems.

Effects of combining biological treatment and activated carbon on hexavalent chromium reduction.

The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (µ(obs)), biomass yield (Y(X/S)), and specific growth substrate consumption rate (q(S)) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (µ(obs), Y(X/S), q(S)). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process.

Effect of type of emulsifiers and antioxidants on oxidative stability, colour and fatty acid profile of low-fat beef burgers enriched with unsaturated fatty acids and phytosterols.

Low-fat beef burgers were formulated using fresh lean meat, 9.9% oleic sunflower oil and 0.1% deodorized fish oil to obtain a product enriched in unsaturated fatty acids. The effect of two emulsifiers (whey proteins or egg white) and natural antioxidants (tocopherols and/or oregano-rosemary), as well as the influence of frozen storage on the oxidative stability, colour, and fatty acid (FA) profile was determined on the cooked products. Whey proteins protected better against oxidation than egg white, and tocopherols demonstrated an adequate antioxidant effect in formulations with egg white. For all the formulations the unsaturated/saturated FA ratio was higher than 5.8, showing a good lipid balance in the products. The consumption of 100g of the cooked product would provide 6% of the recommended daily intake of phytosterols suggested to decrease cholesterol and the risk of heart disease. Formulated low-fat burgers with pre-emulsified oils and phytosterols could be considered to be potentially functional foodstuffs.

Cr(Vi) reduction capacity of activated sludge as affected by nitrogen and carbon sources, microbial acclimation and cell multiplication.

The objectives of the present work were: (i) to analyze the capacity of activated sludge to reduce hexavalent chromium using different carbon sources as electron donors in batch reactors, (ii) to determine the relationship between biomass growth and the amount of Cr(VI) reduced considering the effect of the nitrogen to carbon source ratio, and (iii) to determine the effect of the Cr(VI) acclimation stage on the performance of the biological chromium reduction assessing the stability of the Cr(VI) reduction capacity of the activated sludge. The highest specific Cr(VI) removal rate (q(Cr)) was attained with cheese whey or lactose as electron donors decreasing in the following order: cheese whey approximately lactose>glucose>citrate>acetate. Batch assays with different nitrogen to carbon source ratio demonstrated that biological Cr(VI) reduction is associated to the cell multiplication phase; as a result, maximum Cr(VI) removal rates occur when there is no substrate limitation. The biomass can be acclimated to the presence of Cr(VI) and generate new cells that maintain the ability to reduce chromate. Therefore, the activated sludge process could be applied to a continuous Cr(VI) removal process.

Innovations in the development of healthier chicken sausages formulated with different lipid sources.

Long-chain polyunsaturated n-3 fatty acids are critical nutrients for human health and the fortification of foods with these fatty acids is an important emerging area from the commercial and academic point of view. Development, characterization, and changes during refrigerated vacuum storage of low-fat chicken sausages formulated with preemulsified squid oil were examined and compared with those formulated with beef tallow. Physicochemical analysis and process yield after heat treatment were determined; the heat-treated sausages were evaluated by purge loss, color, texture, microstructure by SEM, microbial counts, fatty acid profile, lipid oxidation, and sensory analysis during refrigerated vacuum storage. Process yield of both formulations was higher than 97% and purge losses during storage were lower than 7%. Purge losses of oil-formulated sausages were lower than those with beef tallow. Sausages with squid oil resulted in higher lightness, lower redness and yellowness, and lower texture profile analysis parameters than the formulation prepared with beef tallow. Microstructure of both formulations was similar, except for the fat droplets that microscopic observations showed in the sausages made with beef tallow. Low lipid oxidation was detected in formulation with squid oil due to the the combination of ingredients and storage conditions. Microbial counts of both products were less than 5 log cfu/g at the end of 90 d of storage. The sausage formulated with squid oil presented more than 30 and 40 g/100 g of monounsaturated and polyunsaturated fatty acids, respectively. Docosahexaenoic acid was the predominant polyunsaturated fatty acid, followed by eicosapentaenoic acid and linoleic acid. Both products showed safe sanitary conditions, good sensory acceptability, and presented very good stability and quality attributes, but sausages formulated with squid oil showed a better fatty acid profile according to nutritional criteria.

Mathematical modelling of microbial growth in ground beef from Argentina. Effect of lactic acid addition, temperature and packaging film.

The effects of: (i) storage temperature (0, 4 and 10°C), (ii) gaseous permeability of the packaging film (polyethylene and EVA SARAN EVA for vacuum packaging), and (iii) natural beef pH (5.6, 5.8 and 6.1) on the growth of different bacteria isolated from beef muscle were examined. The bacteria were Klebsiella, Pseudomonas sp. and Escherichia coli. Microbial growth was modelled using Gompertz and linear equations. The effects of temperature on microbial growth rate (µ) and on lag phase duration were modelled using an Arrhenius type equation. In polyethylene, E. coli was the microorganism, that showed the highest µ values and also the greatest effect of pH on µ, especially in samples stored at 4 and 10°C. In the case of Klebsiella sp., neither pH nor temperature had marked effects on µ and on LPD. In ESE film, µ of all the microorganisms were less affected by pH and temperature than in polyethylene. In ESE film E. coli showed the highest effect of pH on µ, at 4 and 10°C. LPD increased significantly with respect to the values in polyethylene, with Klebsiella sp., showing the highest values of LPD, followed by E. coli. Experiments in ground beef with added lactic acid producing a decrease of the original muscle pH from 6.1 to 5.6 showed that the kinetic parameters of the microbial flora did not differ significantly from those of beef samples in which the original pH was 5.6.

Competitive growth kinetics of Sphaerotilus natans and Acinetobacter anitratus.

Growth kinetics of Sphaerotilus natans and Acinetobacter anitratus (strain E932) in pure and mixed cultures were analysed. In order to determine mixed cultures biomass composition, a quantitative image analysis technique was developed. Pure culture studies showed that for dilution rates less than 0.188 h(-1), the filamentous micro-organism will predominate leading to bulking phenomena. By using the developed technique to determine biomass composition, mixed culture experiments showed that changes in the dilution rate modify the microbial composition of the biomass determining which micro-organism predominate. The stated equations that predict the predominance of S. natans at low dilution rates agree satisfactorily with the obtained results.

Composite starch-based coatings applied to strawberries (Fragaria ananassa).

Starch-based coatings were used to the extend storage life of strawberries (Fragaria ananassa) stored at 0 degree C and 84.8% relative humidity. Effects of coating formulation (including starch type, plasticizer, lipid and antimicrobial agent) were analysed with respect to fruit quality. Plasticizer addition was necessary for film and coating integrity to avoid pores and cracks. Plasticizer presence reduced weight losses and maintained surface colour of fruits. Amylomaize coatings showed lower water vapour and gas permeabilities and decreased weight losses for longer periods than corn starch ones. Coatings with sorbitol showed lower permeabilities than glycerol ones. Coatings with antimicrobial agents decreased microbial counts, extending storage life of coated fruits by 10 to 14 days in comparison to the control. The addition of 2 g/l sunflower oil to the formulations decreased the water vapour permeability of starch-based films, maintained the surface colour of coated fruits and controlled effectively fruit weight losses during storage. Lipid addition minimized the effects of starch and plasticizer types. Composite starch-based coatings showed selective gas permeability (CO2 higher than O2) which helps to delay senescence of fruits.

Size and location of ice crystals in pork frozen by high-pressure-assisted freezing as compared to classical methods.

In high-pressure-assisted freezing, samples are cooled under pressure (200 MPa) to - 20 °C without ice formation then pressure is released (0.1 MPa) and the high super-cooling reached (approx. 20 °C), promotes uniform and rapid ice nucleation. The size and location of ice crystals in large meat pieces (Longissimus dorsi pork muscle) as a result of high-pressure-assisted freezing were compared to those obtained by air-blast and liquid N(2). Samples from the surface and centre of the frozen muscle were histologically analysed using an indirect technique (isothermal-freeze fixation). Air-blast and cryogenic fluid freezing, having thermal gradients, showed non-uniform ice crystal distributions. High-pressure-assisted frozen samples, both at the surface and at the central zones, showed similar, small-sized ice crystals. This technique is particularly useful for freezing large pieces of food when uniform ice crystal sizes are required.

Chemical Preservatives Action on Microbial Growth in a Model System of Refrigerated Prepeeled Potatoes.

The effect of different concentrations of citric acid and ascorbic acid (applied individually or in mixture's) on microbial growth in potato homogenate was analyzed and compared to the sodium bisulfite action during storage at 4°C in low gaseous permeability films. These experiments allowed one to simulate the behavior of prepeeled potatoes but with a known amount of added preservative to evaluate additive or synergic effects. Total viable microorganisms, Enterobacteriaceae , Pseudomonas sp., Lactobacillus sp., molds, yeasts, Clostridium sulfite reducers, psychrotropic microorganisms, and aerobic and anaerobic viable spores were analyzed during storage time. Inhibition indexes produced by the tested preservatives were calculated for the different microorganisms. Sodium bisulfite solutions (100 ppm) had no inhibitory effect. Concentrations of 3,500 ppm citric acid and 10,000 ppm ascorbic acid showed antimicrobial action as well as mixtures of citric acid/ascorbic acid of the following compositions (in terms of total acids concentration): 2,700/2,000, 3,500/2,000, and 2,700/3,000 ppm. A higher effect on Enterobacteriaceae was observed in comparison with other microorganisms. The apparent synergic effect of these acids when they were applied together was demonstrated to be actually an additive effect when concentrations of undissociated acid in the mixtures were considered instead of total concentration.

Ice recrystallization in a model system and in frozen muscle tissue.

Recrystallization produces modifications on ice crystal sizes during storage and transport of frozen foods, reducing the advantages obtained by quick freezing and inducing physicochemical changes which alter their quality and shorten their shelf life. This process involves the growth of the larger crystals at the expense of the smaller ones, being the interfacial energy, the driving force of the phenomenon. In the present work recrystallization was analyzed using direct microscopic observation of ice crystals in a model solution (0.28 N NaCl) and indirect observation of frozen muscle tissue. The model solution allowed visualization of the interface behavior; from the analysis of the ice crystal frequency distributions, relationships between shape and size of the grains were established. A kinetic model based on the average system curvature was proposed obtaining a satisfactory fitness of the experimental data. Values of the kinetic constants determined at different temperatures allowed the estimation of the process activation energy. In muscle tissues isothermal freeze-substitution was used to observe the holes left by the ice in frozen semitendinous beef muscle stored at -5, -10, -15, and -20 degrees C during long periods of time. A different evolution of the mean ice crystal diameter was observed with respect to the model system. In meat samples, at long storage times, a limit diameter value was reached; this situation has been proved to be independent of temperature and initial size (freezing rate); a theoretical expression based on tissue characteristic parameters was proposed for its evaluation. Activation energy for recrystallization in muscle tissue was also determined, being comparable to values for protein denaturation and quality losses.

Rate of freezing effect on the colour of frozen beef liver.

One problem that arises when freezing liver in plate freezers in the whitish colour acquired by the liver surface when subjected to high freezing rates. The purpose of this paper aims to establish optimum operating conditions for freezing beef liver pieces in a minimum time while maintaining an acceptable colour on the surface. Samples were subjected to different freezing rates and minimum surface freezing time was established in order to obtain an acceptable colour. This was quantified in terms of lightness using a surface colorimeter. Histological analysis of the samples showed that the size of the ice crystals formed on the contact surface with the coolant is the factor that determines the changes in colour as a result of diffused light reflection phenomena. On the basis of mathematical heat transfer models with simultaneous change of phase, the minimum characteristic surface freezing time was related to the process operating variables (initial temperature of the liver, coolant temperature, interfacial heat transfer resistance, thickness of the piece), and the optimum freezing conditions were determined, reducing total processing times to a minimum.