Ação de colorantes na degradação e estabilização de polímeros

Dyes and pigments are additives used in polymers to improve mainly the aesthetic properties of the material. However, the incorporation of these additives can directly affect polymer stability. The colorants can drastically decrease the lifetime and the performance of the material or can act as a stabilizer, improving significantly the stability of the polymer against degradation. Interaction between colorants and polymers is the cause of the stability changes. Some mechanisms are proposed to explain the action of colorants on polymers. However it is difficult to foresee this action without experiments. This work reviews the main mechanisms involved in the degradation and stabilization of polymers containing colorants.

Estudo do efeito do tratamento superficial por moagem sobre as propriedades das partículas de uma liga de hidreto metálico

This work reports results of studies on the electrochemical and structural properties of a Ti/Zr-based metal hydride alloy covered by Ni and LaNi4,7Sn0,3 powder additives by ball milling. The effect of this treatment is investigated for the activation time, hydrogen storage capacity and equilibrium pressure, cycling stability and the hydration/dehydration kinetics. Charge and discharge cycles show a significant decrease of the activation time due to an increase of the active area caused by the milling treatment, independent of the additive. However, other results have evidenced little effect of the milling surface treatment on the charge storage capacity, hydrogen equilibrium pressure, and hydration/dehydration kinetics, for both the Ni and LaNi4,7Sn0,3 covered materials.

Teores de corantes artificiais em alimentos determinados por cromatografia líquida de alta eficiência

Synthetic dyes are much used in processed foods. HPLC was applied to different types of snacks, such as colored cereals, chocolate confetti, chewing gums and candies for the determination of those additives. In the case of artificially colored breakfast cereals, 71% of the samples exceeded the allowed limits. Regarding the portions recommended for consumption by the makers of two of the samples, the amounts exceeded those allowed by the Brazilian legislation. In the case of chocolate confetti and candies none of the samples showed higher amounts than those allowed. However 37% of the chewing gum samples presented larger contents than the authorized ones, and one sample contained five times more synthetic dyes than allowed.

Redução de vitamina C em suco de caju (Anacardium occidentale L.) industrializado e cajuína

Vitamin C degradation was evaluated in industrialized cashew juice of high pulp content and in cajuina by the method of Tillmans during eleven days of storage after the opening of the flask. For recently opened juices, vitamin C was found in the concentration range of 112 to 170 mg for 100 g of juice. The degradation of vitamin C in industrialized cashew juices changes when different additives are used. All of the cajuinas presented a vitamin C content below that specified on the label.

Determinação de misturas de sulfametoxazol e trimetoprima por espectroscopia eletrônica multivariada

In this work a multivariate spectroscopic methodology is proposed for quantitative determination of sulfamethoxazole and trimethoprim in pharmaceutical associations. The multivariate model was developed by partial least-squares regression, using twenty synthetic mixtures and the spectral region between 190 and 350 nm. In the validation stage, which involved the analysis of five synthetic mixtures, prediction errors lower that 3% were observed. The predictive capacity of the multivariate models is seriously affected by spectral changes induced by pH variations, a fact that acquires a great significance in the analysis of real samples (pharmaceuticals) that contain chemical additives.

Análise dinâmico-mecânica: aplicações em filmes comestíveis

Edible films are thin materials based on biopolymers and food additives. The aim of this work is a review on the application of dynamic mechanical analysis in edible film technology. After a brief review of the linear visco-elasticity theory, a description of some practical aspects related to dynamic mechanical analysis, such as sample fixation and sample dehydration during analysis and types and modes of tests are presented. Thus, the use of temperature scanning analysis for glass transition and for plasticizer-biopolymer compatibility studies and frequency scanning tests, less common in edible film technology, are critically reviewed.

A espectrometria atômica e a determinação de elementos metálicos em material polimérico

Polymeric materials are widely used in the chemical industry and are part of our daily lives. Inorganic species may be added to them as additives, anti-oxidizing agents, stabilizers, plasticizers, colorants and catalysts and may be present in a wide range of concentrations. Their determination demands the development of analytical methods considering different kinds of polymeric materials, their composition and the final use of the material. Although many different analytical techniques may be used, this review emphasizes those based on atomic absorption and emission spectrometry. Solid sampling techniques and digestion methods are described and discussed and compared considering published results.

Determinação simultânea de cátions empregando eletroforese capilar com detecção condutométrica sem contato em equipamento construído em laboratório

This work describes the development of a home-made capillary electrophoresis (CE) system based on the capacitively coupled contactless conductivity detection (C4D) for the separation of the metallic species Zn2+, Cr3+, Pb2+, Cd2+, Co2+, Cu2+, Ni2+ e Tl+. A background electrolyte composed of MES/Histidine 0,02 mol L-1 (pH 5.0) was optimized for the separation of the metallic species by using organic solvents and complexing agents as additives. The system allowed the determination of the metallic species using MES/Histidine 0,02 mol L-1 and methanol 5% (pH 5.0) as a background electrolyte, 15 kV separation voltage and hydrodynamic injection by gravity.

Determinação do ponto de névoa em surfactantes não iônicos por espectroscopia de impedância elétrica

In this paper, we analyze the use of electrical impedance spectroscopy applied to determination of cloud point. The slope of admittance measured at 100 kHz is reduced to temperature above the critical value which characterizes the phase transition, in a strong indication that this process is activated during the clouding. Additionally to this study we explored the influence of parameters such as additives and temperature on the performance of phase separation of residues (silver nanoparticles) by cloud point extraction. The interaction with salt maximizes the separation of chemical residues in a progressively reduced temperature.

Estudo comparativo da caracterização de filmes biodegradáveis de amido de mandioca contendo polpas de manga e de acerola

Most compounds reinforcements have been used to improve thermals, mechanical and barrier properties of biopolymers films, whose performance is usually poor when compared to those of synthetic polymers. Biodegradables films have been developed by adding mango and acerola pulps in different concentrations (0-17,1% w/w) as antioxidants active compounds to cassava starch based biodegradable films. The effect of pulps was studied in terms of tensile properties, water vapor permeability, DSC, among other analysis of the films. The study demonstrated that the properties of cassava starch biodegradable films can be significantly altered through of incorporation mango and acerola pulps.

Glicerólise de óleo de peixe catalisada por lipase comercial de Rhizomucor miehei em meio com surfactante de grau alimentício

Omega-3 enriched partial acylglycerols are beneficial for human health. The aim of this study was to obtain monoacylglycerols (MAG) and diacylglycerols (DAG) by means of glycerolysis of fish oil catalyzed by a lipase from Rhizomucor miehei in the presence of food grade surfactants (Tween 65, 80 or 85). Glycerolysis was successful in the reaction media for all the tested surfactants, showing their potential for use as additives in such a system. The best results, however, were obtained for the reaction medium in the absence of surfactant whose peroxide value was the lowest after glycerolysis.

Grape juice quality control by means of ¹H nmr spectroscopy and chemometric analyses

This work shows the application of ¹H NMR spectroscopy and chemometrics for quality control of grape juice. A wide range of quality assurance parameters were assessed by single ¹H NMR experiments acquired directly from juice. The investigation revealed that conditions and time of storage should be revised and indicated on all labels. The sterilization process of homemade grape juices was efficient, making it possible to store them for long periods without additives. Furthermore, chemometric analysis classified the best commercial grape juices to be similar to homemade grape juices, indicating that this approach can be used to determine the authenticity after adulteration.

USO DE SÍLICAS MODIFICADAS PARA IMOBILIZAÇÃO DE LIPASES

Enzyme-support strategies are increasingly replacing conventional chemical methods in both laboratories and industries with attributes including efficiency, higher performance and multifarious use, where silica surfaces show potential due to the chemical bonds based on the presence of hydroxyl groups which can be modified with different additives. Surface-modified silica is a novel class of materials capable of improving enzyme stability and reusability that can be applied to support several immobilization techniques. This review describes the use of innovative modified supports to improve the state of enzyme immobilization and provide the industrial sector with new perspectives.

MICROEMULSÕES: COMPONENTES, CARACTERÍSTICAS, POTENCIALIDADES EM QUÍMICA DE ALIMENTOS E OUTRAS APLICAÇÕES

Microemulsions (MEs) are thermodynamically stable systems consisting of nanosized droplets dispersed in a solvent continuous medium (known as pseudo-phase), which is immiscible with the dispersed phase. These systems consist of water, a hydrophobic solvent called "oil," an amphiphile and often, a co-surfactant that is normally a medium chain alcohol. A large number of publications describe the importance of MEs in many branches of chemistry, and there is an intensive search for new applications. In addition, MEs have been applied in many areas, including oil extraction, removal of environmental pollutants from soils and effluents, dissolution of additives in lubricants and cutting oils, cleaning processes, dyeing and textile finishing, as nanoreactors to obtain nanoparticles of metals, semiconductors, superconductors, magnetic and photographic materials, and latex. However, only some studies indicate the potential applications of MEs in food and even fewer evaluate their chemical behavior. Potential applications of MEs in food comprise dissolution of lipophilic additives, stabilization of nutrients and biologically active compounds, using as an antimicrobial agent and to maximize the efficiency of food preservatives. This work consists of a literature review focusing on composition and physical and chemical characteristics of microemulsions. Despite the small number of studies on the subject reported in the literature, we demonstrate some potential applications of MEs in food chemistry.

"Cara inchada" of cattle, an infectious, apparently soil antibiotics-dependant periodontitis in Brazil

The objective of this review on the investigation of "cara inchada" in cattle (CI), pursued over the last 30 years, was to elucidate the pathogenicity of the disease and come to proper conclusions on its etiology. CI has been widely considered to be of nutritional origin, caused primarily by mineral deficiency or imbalance. However, the disease consists of a rapidly progressive periodontitis, affecting the periodontal tissues at the level of the premolars and molars during the period of tooth eruption generally starting in young calves. The disease led to great economic losses for farmers in central-western Brazil, after the occupation of new land for cattle raising in the 1960s and 1970s. The lateral enlargement of the maxillary bones of affected calves gave the disease the popular name of "cara inchada", i.e., swollen or enlarged face. The enlargement was found to be due to a chronic ossifying periostitis resulting from the purulent alveolitis of CI. Black-pigmented non-saccharolytic Bacteroides melaninogenicus, always together with Actinomyces (Corynebacterium) pyogenes, were isolated in large numbers from the periodontal lesions. B. melaninogenicus could be isolated in small numbers also from the marginal gingiva of a few healthy calves maintained on CI-free farms. "In vitro"-assays showed that streptomycin and actinomycin, as well as the supernatants of cultivates of actinomycetes from soils of CI-prone farms, applied in subinhibitory concentrations to the bacteria tested, enhanced significantly (up to 10 times) the adherence of the black-pigmented B.melaninogenicus to epithelial cells of the bovine gingiva. The antibiotics are apparently produced in large quantities by the increased number of soil actinomycetes, including the genus Streptomyces, that develop when soil microflora are modified by cultivating virgin forest or "Cerrado" (tree-savanna) for the first time for cattle grazing. The epidemiology of CI now provides strong evidence that the ingestion with the forage of such antibiotics could possibly be an important determinant factor for the onset and development of this infectious periodontitis. The antibiotic enhanced adherence of B.melaninogenicus to the sulcus-epithelium of the marginal gingiva, is thought to allow it to colonize, form a plaque and become pathogenic. There is experimental evidence that this determinant factor for the development of the periodontitis is present also in the milk of the mothers of CI-diseased calves. It has been shown that the bacteria isolated from the periodontal CI-lesions produce enzymes and endotoxins capable of destroying the periodontal tissues. The epidemiology of CI, with its decline in incidence and its disappearance after several years, could be explained by the fact that the former equilibrium of the microflora of the once undisturbed virgin soil has been reached again and that the number of antibiotic producing actinomycetes has been anew reduced. By this reasoning and all the data available, CI should be considered as a multifactorial infectious disease, caused primarily by the anaerobic black-pigmented non-saccharolytic Bacteroides melaninogenicus, always together with the micro-anaerobic Actinomyces pyogenes. Accordingly, the onset and development of the infectious periodontitis is apparently determined by ingestion with the forage of subinhibitory concentrations of antibiotics produced in recently cultivated virgin soils. This hypothesis is supported by the recent observation of renewed outbreaks of CI-periodontitis in former CI-prone areas, following fresh cultivation after many years. The infectious nature of CI is confirmed by trials in which virginiamycin was used efficiently for the oral treatment of CI-diseased cattle. Previously it has been shown, that spiramycin and virginiamycin, used as additives in mineral supplements, prevented CI-periodontitis.