In this work the vitamin C was determined in industrialized nectar juices through ultraviolet (UV) spectroscopy and multiproduct multivariate calibration, based on partial least squares (PLS) regression. Since samples with different flavors, sugar content (light or not) were together in the model construction, it can be considered as a multiproduct and, due to the heterogeneity of the samples, it was necessary to optimize the calibration and validation sets by outliers elimination. The model was developed and validated by the evaluation of the figures of merit such as: accuracy, sensitivity, analytical sensitivity, adjust, linearity, relative prediction deviation, limits of detection and quantification, indicating that the multiproduct model developed from UV spectroscopy and PLS regression can be used in the industrial routine analysis as an alternative to titration or other time and reagent consuming methods. Here, it was evidenced that the UV-PLS multiproduct model provides advantages as being free of sample preparation steps, is suitable to be updated in order to measure other parameters, does not generates residues and is feasible to be implemented for on-line monitoring. Furthermore, the application of multivariate calibration in multiproduct models is extremely attractive from the industrial point of view.
<p>The determination of the total acid using UV spectroscopy and multi-product multivariate calibration is presented as an alternative to the conventional method through potentiometric titration. The model was developed including different products (fruit nectar of different flavors and light fruit nectar) where outliers samples were identified and excluded. Partial least squares (PLS) regression was used in order to build the model. Accuracy, represented by the values of the Root Mean Squared Errors of Calibration (RMSEC) and Prediction (RMSEP) were 0.0641 and 0.0534 mg/100 mL, respectively. The confidence ellipse confirms that accuracy was achieved at 99 % confidence, while residues showed random behavior, confirming linearity for the model developed. The proposed methodology shows advantages as fastness, does not requires sample preparation and does not generate toxic waste, being an alternative to the conventional method based on potentiometry.</p><p> </p><p>DOI: 10.14685/rebrapa.v6i1.177</p>
Total acidity and vitamin C were determined by using ultraviolet spectroscopy and multi-product multivariate calibration alternately to the reference methods, the potentiometry and Tillman's, respectively. In the developed multi-products models, different products were included (industrialized juices based on soya of different flavors and light). The linear partial least squares (PLS) method was used in the model construction and the outlier samples were evaluated. The accuracy at the 99% level, represented by the root mean square error of calibration (RMSEC) and prediction (RMSEP), was confirmed through the confidence ellipse, whereas the residuals presented random behavior, which indicates that the data fit a linear model. Sensitivity and analytical sensitivity presented adequate results in the determination of vitamin C and acidity, considering the concentration range used 0.83-16.83 mg 100 mL-1 for vitamin C and 0.17-0.34 g 100 mL-1 for total acidity. The inverse of the analytical sensitivity shows that it is possible to distinguish samples with difference in vitamin C concentration of the order of 0.73 mg 100 mL-1, and samples with difference in total acidity of the order of 6.1 x 10-3 g 100 mL- 1.The multi-product PLS model present limits of detection and quantification for vitamin C of 2.43 and 7.36 mg 100 mL-1, respectively. For total acidity, the limits of detection and quantification achieved were 0.02 and 0.06 mg 100 mL-1, respectively. The values for residual prediction deviation (RPD) presented results within the range of values, which classify the models as satisfactory. In addition, the multi-product calibration is fast, because it does not require reagents/solvents and does not generate toxic waste, being an alternative to the conventional methods and being in agreement with the requirements of green chemistry.
RESUMO -O PLS foi aplicado a espectros ultravioleta para o desenvolvimento de um modelo de calibração multivariada multiproduto para a determinação da acidez total em bebidas industrializadas a base de soja e néctar de frutas. O objetivo foi propor uma metodologia alternativa à potenciometria. Para aquisição dos espectros utilizou-se uma cubeta de quartzo de 1mm. Um total de 249 amostras foi utilizado, 126 bebidas a base de soja e 123 néctar de frutas. O algoritmo Kennard-Stone foi empregado na separação das amostras em conjuntos de calibração (185) e validação (64) e as amostras anômalas foram identificadas de acordo com a ASTM E1655-05. O modelo foi construído com 5 variáveis latentes e mostrou exatidão, representada pelos valores dos erros médios quadráticos de calibração (RMSEC) e validação (RMSEP) de 0,049 e 0,045 mg/100mL, respectivamente. Um teste t-pareado mostrou que não existe diferença significativa entre os dois métodos, no nível de confiança de 95%.
INTRODUÇÃOÉ sabido que a determinação da acidez total de bebidas industrializadas a base de soja e de néctar de frutas propicia informações sobre o estado de conservação do produto. E essa acidez, atualmente é quantificada por um método clássico, a potenciometria; entretanto, essa metodologia é relativamente demorada e gera resíduos devido aos reagentes utilizados. Visando tornar o processo de quantificação da acidez total dessas bebidas industrializadas mais eficiente, percebe-se que o modelo de calibração multivariada, em que se aplica o método de mínimos quadrados parciais (PLS) em espectros ultravioleta de tais produtos, pode ser um substituinte da metodologia tradicional aplicada. Isso ocorre devido a robustez do novo método, que além de ser mais rápido e proporcionar resultados eficazes, também evita a geração de resíduos, uma vez que não é necessário preparo de amostras.Considerando as bebidas industrializadas a base de soja e néctar, pode-se saber qual o estado de conservação do item em questão a partir da acidez total. A acidez dessas substâncias pode ser influenciada por processos de decomposição, sejam eles hidrolise ou fermentação, que alteram quase sempre a concentração dos íons hidrogênio. (VENÂNCIO e MARTINS, 2012 e INSTITUTO ADOLFO LUTZ, 2008. Quanto à maneira de se determinar a acidez é comum realizar a titulação da bebida com uma solução básica de concentração conhecida. Porém, esse processo demanda o uso de reagentes, geram resíduos que podem colocar em risco o analista e o meio ambiente, destroem a amostra, entre outros.Área temática: Engenharia e Tecnologia de Alimentos 1
We examine the potential of ultra-high-performance supercritical fluid chromatography for multiresidue quantification of ten pesticides commonly applied to lettuce and compares it to ultra-high-performance liquid chromatography. Initially, a thorough study of the stationary and mobile phase composition and injection solvent was carried out. In a second step, a chemometric approach based on design of experiments was used to simultaneously study the influence of temperature, pressure, and percentage of ethanol on the retention, resolution and symmetry of the peaks. Using this approach, it was possible to obtain the Design Space, a robust region where complete separation of the analytes was achieved, with acceptable peak shape. Both methods were validated according to the figures of merit: selectivity, linearity, quantification limit, accuracy (in terms of recovery), and precision (repeatability and intermediate precision) and used to quantify the pesticides in lettuce samples. Comparing both techniques, it was concluded that the limits of quantification, accuracy, and precision were similar. However, in supercritical fluid chromatography, a reduced volume of organic solvent was used, the method was faster and generated lower amounts of residues.
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