Determinação elementar, fração bioacessível e proteínas em amostras de carne ovina in natura e termicamente processadas

Abstract

Sheep meat is a source of manifolds nutrients such as proteins and essential chemical elements as Ca, Fe, K, Mg, P and Zn, however, it may have non-essential chemical elements such as Cd and Pb. The presence of these elements may come from the nurture system, location of the flock and slaughter age. Before being consumed, meat can undergo different heat treatments such as cooking in water, frying, roasting, among others. The different treatments can change the availability of nutrients, such as proteins and essential elements, and may interfere with the absorption of these nutrients by the digestive system, in other words, their bioaccessibility. In this scenario, the present work aims to optimize a method of acid decomposition in a reflux system to determine the elemental concentration of Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na and Zn by the emission spectrometry technique Microwave induced plasma optics (MIP OES) in samples of Sheep meat submitted to three heat treatments (cooking in water, microwave and conventional oven) and the bioacessible fraction after heat treatment. In addition, it is intended to determine the concentration of Cd and Pb by the technique of atomic absorption spectrometry with graphite furnace (GF AAS) and also the percentage of proteins in the samples of sheep meat by the Kjeldahl method, for this, the best conditions of decomposition , using the reflux system, were optimized through a multivariate design that evaluated the independent variables (decomposition time, digester block temperature and H2O2 volume). Sample mass and volume of HNO3 were fixed at 1 g and 5 mL, respectively. The best decomposition conditions obtained for the elements Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na and Zn were 140 °C for temperature, 187 min for time and 1.8 mL of H2O2, which were determined by MIP OES and Cd and Pb by GF AAS. The accuracy of the results was evaluated using certified meat reference materials and the values obtained were consistent with the certified values according to Student's t-test at 95% confidence. For Al and Ba, an analyte addition test was performed and recoveries ranging from 83 to 110% were obtained. In natura samples, concentrations ranged from 2.77 to 6.69 mg kg -1 for Al; 0.25 to 0.27 mg kg -1 for Ba; 0.95 to 2.75 mg kg -1 for Cu; 33.5 to 111 mg kg -1 for Fe; 3,609 to 5,697 mg kg -1 for K; 202 A 381 mg kg -1 for Mg; 0.113 to 0.711 mg kg -1 for Mn; 329 to 771 mg kg -1 for Na and 31.2 to 99.4 mg kg -1 for Zn. Pb showed values below the detection limit of the method in all samples. Cd, on the other hand, presented concentrations ranging from 16.9 to 96.8 μg kg-1. Regarding heat treatments, the microwave method was the one that presented the lowest losses of elements. The conventional oven presented the highest losses for Al, Ca, Fe and Zn and cooking in water for K, Mg and Na. The Mn, Cd and Pb values were below the method detection limit for the three heat treatment methods. The bioacessible fraction was greater than 50% for K in the three heat treatments; for Cu and Mg the highest bioacessible fractions were in the oven treatment, ranging from 46 to 83% and 39 to 98%, respectively. Fe presented the highest bioacessible fraction in the microwave treatment, ranging from 15 to 31% and Zn was the element that presented the lowest bioacessible fractions for the three treatments, ranging from 0.2 to 3.2%; 0.7 and 3.2% and 0.9 and 25% for samples cooked in water, baked in microwave oven and conventional oven, respectively. Protein content varied from 18 to 20.5% for fresh lamb meat and a higher percentage in samples treated in the microwave oven from 33.35% to 49.93% (g/100g). Therefore, these results indicate that different cooking methods affect the chemical composition and nutritional value of meat. However, the microwave preparation method presents itself as a better preparation alternative, preserving more the nutritional characteristics of the meat.