AVALIAÇÃO DA QUALIDADE FÍSICO-QUÍMICA DE POLPAS DE FRUTA CONGELADAS COMERCIALIZADAS NA CIDADE DE CUIABÁ-MT

RESUMO O presente trabalho teve como objetivo avaliar a qualidade físico-química das polpas de frutas congeladas comercializadas na cidade de Cuiabá-MT, comparando com os padrões estabelecidos pela legislação vigente. O experimento foi desenvolvido em delineamento inteiramente casualizado, sendo cinco tratamentos (marcas denominadas A, B, C, D e E) e três repetições, para as polpas de abacaxi, acerola, caju, goiaba e maracujá. Foram analisados os parâmetros pH, acidez titulável expressa em ácido cítrico, sólidos solúveis, ratio, vitamina C, açúcar redutor e quantificação da perda de vitamina C após 90 dias de armazenamento sob congelamento, em polpas de acerola e caju. Os dados obtidos foram submetidos à análise de variância, e as médias, comparadas pelo teste de Tukey, ao nível de 5% de probabilidade. A marca D apresentou não conformidade com a legislação para todas as polpas em, pelo menos, um dos parâmetros avaliados. Foi observado maior número de amostras em inadequação para o teor de vitamina C e, de forma geral, as polpas avaliadas apresentaram valores abaixo das especificações exigidas pelos Padrões de Identidade e Qualidade (PIQ) para as mesmas. Todas as amostras avaliadas tiveram redução do teor de vitamina C durante armazenamento sob congelamento, sendo que nenhuma marca de polpa de acerola e apenas uma de caju apresentou, ao final de 90 dias, teor de vitamina C de acordo com o estabelecido pelo PIQ. Conclui-se que é necessária uma intensificação na fiscalização no processamento de polpas de frutas congeladas para garantia da saúde do consumidor.

Aplicação da cromatografia por exclusão e da cromatografia gasosa de alta resolução na análise do café

The combination of high performance exclusion chromatography (HPEC) and gas chromatography (GC) was applied to the analysis of six coffee samples that were previously characterized by sensory tests as of good or poor quality. The data obtained by the two techniques were statistically evaluated by "Principal Components Analysis" (PCA) using selected peak areas. The results showed the potential of the described techniques for coffee analysis. The HPEC technique monitored with the U.V. detector at 272 nm and followed by PCA may be correlated with sensorial data, particularly if a wider group of samples is used.

Análise potenciométrica de redissolução com ultramicroeletrodos: fundamentos e aplicações na determinação de metais traços

The Potentiometric Stripping Analysis (PSA) is described with emphasis on ultramicroelectrode applications with a laboratory developed computer based instrumentation. The technique potentialities as compared with the voltammetric approach are pointed out based on the current literature. Some results of trace metals analysis including zinc, cadmium, lead and copper in vinegar and canned food samples are presented. The mainly advantage found in our laboratory was the technique capability to analyse natural samples with minimum matrix interference and the low level of noise found in our determinations.

Modificação de um micro-extrator de vidro para pré-enriquecimento de traços de pesticidas organoclorados de água para análise por cromatografia gasosa

Two models of a glass micro-extractor were constructed after modification of a model proposed in the literature. The two models were used for the simultaneous extraction and enrichment of organochlorinated pesticides from aqueous matrixes to an organic solution appropriate for the gas chromatographic analysis of the pesticide. It was established that the performance of one of the modified micro-extractors permits the pre-concentration of the pesticides to a level that allow their quantitation at the trace level with electron capture detection. It is thus concluded that the glass micro-extractor is a suitable tool for the sample preparation step in the gas chromatographic analysis of environmental pollutants of the class of pesticides.

Construção e avaliação de um eletrodo tubular sensível ao íon hidrogênio como detector em sistemas de análise em fluxo

The construction of a tubular hydrogen ion-selective potentiometric electrode without inner reference solution, based on the tridodecylamine (TDDA) ionophore, and its evaluation in a flow system are described. TDDA was dissolved in 2-nitrophenyl octyl ether, dispersed in a PVC membrane and applied directly to a conducting support which consisted of an epoxy resin and graphite mixture. The electrode was designed with a tubular geometry to effort facilities to be coupled as part of a flow injection network. The main working characteristics such as response time, linear pH range, selectivity and life time were evaluated and compared with those obtained which a conventionally shaped electrode based on the same sensor. The electrode showed a slope of 51-52 mV dec-1 within a linear pH range from 4.0 up to 12.0.

Estudo de métodos de aumento de resolução de espectros de FTIR para análise de estruturas secundárias de proteínas

The FTIR spectroscopy has been used to quantify the secondary structures of proteins, using amide I band (1600 - 1700 cm-1). The resolution enhancement methods have been used to resolve the individual components of this band that correlate to the secondary structure. In this paper we discuss the methods of derivative, Fourier deconvolution and fitting with simulated spectra. The results shows that they have serious problems and can be used only as a qualitative or semiquatitative method.

Gotas suspensas: uma proposta para amostragem e análise de gases traços da atmosfera

In the present paper, we report on the analytical use of a dynamic droplet based gas collection and an analysis system. A droplet formed at the tip of a tube represents a sampling approach that provides an indefinitely renewable surface and uses very little reagent. Sample gas flows past the droplet at a low flow rate. After the gas was sampled , the analysis can be carried out by different methodologies. The feasibility of the sensor is demonstrated by continuos determination of gaseous as: NO2, Cl2 and SO2.

Cinética não-isotérmica na análise térmica de sólidos

In this work, a computer program called Thermal Kinetics was implemented to simulate thermal analysis experiments by numerical integration of the kinetics equations. The computer program was tested in two different examples: non-isothermal transformation of a Cu-Al alloy and non-isothermal decomposition of calcium oxalate monohydrated. In spite of the rather crude approximations of the model, the simulated profiles are very similar to the experimental curves. Both, the dalpha /dt and the dalpha /dT profiles reproduce the experimental transition temperatures with an error smaller than 25%.

Análise das isotermas de adsorção de Cu(II), Cd(II), Ni(II) e Zn(II) pela N-(3,4-dihidroxibenzil) quitosana empregando o método da regressão não linear

Adsorption of Cu(II), Ni(II), Pb(II) and Zn(II) ions from aqueous solutions by N-(3,4-dihydroxybenzyl) chitosan have been carried out. The Langmuir (L), Freundlich (F), Langmuir - Freundlich (LF), Redlich-Peterson (RP) and Tóth (T) adsorption isotherms models have been applied to fit the experimental data. Nonlinear regression computational program "Enzefitte", which is a library of the more commonly used adsorption isotherm equations for obtaining tabular outuput suitable for plotting theoretical of fitted isotherms, has been used to estimate the adsorption parameters. These parameters were used to calculate the amount adsorbed q calc., a function of concentration (C).

Amostragem de suspensões: Emprego da técnica na análise direta de amostras

This review presents some characteristics related to slurry sampling in trace analysis in terms of its advantages, limitations and applications, as well as the latest advance in this area, such as mechanization, chemical modifiers, stabilization agents and others. The reviewed applications include foods, biological and geological materials.

Uma introdução à análise exploratória de dados multivariados

The modern technological ability to handle large amounts of information confronts the chemist with the necessity to re-evaluate the statistical tools he routinely uses. Multivariate statistics furnishes theoretical bases for analyzing systems involving large numbers of variables. The mathematical calculations required for these systems are no longer an obstacle due to the existence of statistical packages that furnish multivariate analysis options. Here basic concepts of two multivariate statistical techniques, principal component and hierarchical cluster analysis that have received broad acceptance for treating chemical data are discussed.

Calibração multivariada para sistemas com bandas sobrepostas através da análise da fatores do tipo Q

A multivariate calibration method to determine chemical compositions of systems with severely overlapped bands is proposed. Q mode factors are determined from the spectral data and subsequently rotated using the varimax and oblique transformation of Imbrie. The method is applied to two sets of simulated data to test the sensitivity of analytical results to random experimental error. The chemical concentrations of alanine and threonine mixture are determined from spectral data of the 302,5 - 548,5 nm region.

Aplicação de SPME (Solid Phase Micro-Extraction) na análise de águas potáveis de três localidades do estado de São Paulo

The technique of solid phase microextraction (SPME) was used for the extraction of halogenated contaminants of water samples from three cities of the State of São Paulo and the extracts were submitted to gas chromatographic analysis with electron capture detection (GC-ECD). In the samples of water collected at the city of São Paulo the detected level of trihalomethanes (THM) expressed as the sum of chloroform, dibromochloromethane and dichlorobromomethane, were higher than the permissible limit established by the Brazilian regulation. In the samples collected at the two other cities the level of any of the three THM remained below the sensitivity of the ECD.

Sistema automático para análise direta de ligas metálicas por eletrodissolução anódica e espectrometria de absorção atômica

An automatic system for the direct determination of lead and tin by atomic absorption spectrometry is described. The on-line treatment of the metallic samples was obtained by anodic electrodissolution in a flow injection system. Lead was determined by flame atomic absorption spectrometry (FAAS) and tin by graphite furnace atomic absorption spectrometry (GFAAS). A computer program managed the current source and the solenoid valves that direct the fluids. Good linear correlations between absorbance and current intensity for lead and tin were observed. Results were in agreement with the certified values. Precision was always better than 5%. The recommended procedure allows the direct determination of 60 or 30 elements/h using FAAS or GFAAS, respectively.

Identificação de componentes de óleos voláteis: Análise espectroscópica de misturas de sesquiterpenos

This paper describes a chromatographic method to fractionate volatile oils and to identify their sesquiterpenic constituents. The fractionation process includes flash chromatography over silica gel and chromatography over silica gel/AgNO3, utilising pentane, CH2Cl2 and/or acetone as eluents. GC chromatograms were obtained in order to get the relative percentage of each constituent in the volatile oils, to get the retention time value of them as well as to analyse and combine the fractions eluted from the columns. Such procedure afford mixtures of sesquiterpenes which are analysed by GC/MS, 13C and ¹H NMR.