DESENVOLVIMENTO E VALIDAÇÃO DE MÉTODOS DE EXTRAÇÃO ASSISTIDA POR ULTRASSOM APLICADA NA DETERMINAÇÃO DE Fe, Mn, Mg, Ca E P EM MELADO DE CANA

Abstract

Cane syrup, made from process of evaporation of sugarcane juice, is a byproduct of sugarcane. It is also considered a food with elevated sugars and minerals contents. Therefore, it is important to know the mineral composition of this food, considering there are few studies in the literature about of this product. Thus, the purpose of this study was developed methodologies based in the ultrasound assisted extraction for determination of Fe, Mn, Ca, Mg and P in cane syrup samples by Atomic Absorption Spectrometry in Flame (F AAS) and Molecular Spectrometry in the UV-VIS region. A simplex centroid mixture design was applied in order to determine the optimal proportion of extractor solvent (nitric acid, hydrochloric acid and water) through of statistics models and then get extraction rates close to 100% for these elements. Optimal extraction condition for Fe, Mn, Ca, Mg and P was obtained with sample mass of 0.5 g, power of 100 W, frequency of 37 kHz and 10 minutes of sonication at temperature of 25 °C. For Fe and Mn extractions, the optimal condition was obtained with 5.00 mL H2O; the best proportion evaluated for Ca and Mg extractions was the proportion of 75:25 % (v/v) of HNO3:H2O as extractor solvents and for P extraction, the optimum condition was obtained with the proportion of 34:40:26 % (v/v) of HNO3:HCl:H2O as extractor solvents, respectively. Distinct comportment of the extractor solvents was attributed the different way that metals are bound in the cane syrup. Thus, mixture design allowed a quick and efficient optimization of composition extractor solvents used in this procedure. Reliability of ultrasound assisted extraction methods to the determination of metal was verify by a validation study in which were evaluated parameters such as linearity, limits of detection (LOD) and quantification (LOQ), precision and accuracy, applying different statistic tests. Analytical curves obtained by external standardization were employed for all elements. They showed good linearity, with values of Fregression ˃˃ Fcritical, and values of p < 0.05, without lack of fit for the linear model and determination coefficients (R2) between 92.2 and 99.8 %. LOD and LOQ values were relatively low, with LOD values of 0.266, 0.284, 0.037, 0.282 and 0.296 μg g-1 for Fe, Mn, Mg, Ca and P; with LOQ values of 0.805, 0.861, 0.114, 0.854 and 0.898 μg g-1 for Fe, Mn, Mg, Ca and P, respectively. Precision was verified by repeatability and intermediate precision estimates, using the relative standard deviations (RSD %) and Horrat values. RSD % values were considered appropriate, lower ones than those recommended by AOAC (< 11%), with Horrat values < 1.3. Accuracy was evaluated by comparison between ultrasound assisted extraction methods and microwave digestion method (reference method) applying a paired t-test. It was not observed significant statistical differences between the compared methods to determination Fe, Mn, Mg, Ca and P at 95% confidence level, with values of tcalculated < tcritical and value of p ˃ 0.05. These facts indicated that ultrasound assisted extraction methods show exact and precise results in order to quantification these elements in cane syrup samples. In addition, the ultrasound assisted extraction is an alternative sample preparation method when compared with conventional methods, because it was faster, produce lesser residues generation through lesser solvents consume, lower environment impact, lower risks to analyst, furthermore being of low cost. Thus, methodologies developed in this study becomes attractive to the implantation in food analysis laboratories, allowing the monitoring of minerals levels in sugar rich foods, such as cane syrup, ensuring a better control quality of the product. Through the Principal Component Analysis (PCA), was possible to verify that there are a grouping trend in analyzes of the elements in the cane syrup samples, according with product origin, showing that factors such as raw material, climate, soil and processing adopted for manufacturer of the certain region, influence final metals contents in the product.