DESENVOLVIMENTO E VALIDAÇÃO DE METODOLOGIAS TERMOGRAVIMÉTRICAS PARA A DETERMINAÇÃO DE ÁGUA EM ALIMENTOS RICOS EM AÇÚCARES

Abstract

The most of processed food has water in its chemical composition, and depending on the water content in it, its quality may be compromised. The shelf life of a food product can be significantly reduced due to the presence of excess moisture and permeable packaging for light and oxygen. Therefore, moisture analysis in a food is extremely important, however, to date there is no universal method that is both accurate and precision for different types of food. This fact is due to the difficulties encountered in incomplete separation from the other constituent components of food. This paper presents the optimization and validation of thermogravimetric methods for determining the water content in foods rich in sugars, such as brown sugar, molasses syrup, syrup, fruit juice and fruit jelly. Each of these foods has a specific characteristic which requires special care in determining the water content. To the brown sugar thermogravimetric ideal drying conditions were: heating rates 5 ° C min-1; alumina sample holder, dynamic atmosphere of air (50 ml min-1) and 5.0 mg of sample. The proposed method showed adequate accuracy and precision. Since the data of the official method validation study (loss on drying) to the brown sugar showed that its precision is comparable with thermogravimetry and Karl Fischer titration, but its accuracy is affected by systematic errors whose magnitude depends on the chemical composition of brown sugar. The results of optimization study by the factorial design for the molasses syrup suggest that heating rates of 5 ° C min-1 and the use of glass fiber paper are more suitable for this type of food. These conditions provide better heat transfer in the sample during drying, minimizing the influence of degradation reactions on water content removal contained in the food and consequently the effect of case hardening that insert systematic errors in this type of determination. It also performed the application of isothermal thermogravimetric to the development of a new method of loss on drying for molasses syrup, which showed accuracy and precision as compared to the Karl Fischer titration method. The syrup samples were more sensitive with respect to use of glass fiber paper and the heating rate because it was not possible to analyze them at a heating rate of 10 ° C min-1, and without the use of paper. It was also necessary to reduce the mass generally used from 5.0 mg to 3.0 mg to minimize the bubbling effect of the sample and consequent projection of the sample holder into the furnace TG/DTA. The results of the optimization by factorial design studies suggest that a heating rate of 5 ° C min-1 and the use of glass fiber paper are more suitable for drying the samples thermogravimetric processed fruit products. These conditions provide better heat transfer in the sample during drying, minimizing the influence of degradation reactions in the water removal. The validation study demonstrated by different statistical techniques (t-test and F-test) that thermogravimetry showed adequate accuracy and precision for determining the water content in the investigated food, since they were not observed systematic errors and significant random with respect to the Karl Fischer titration method used in this work as reference method. The use of thermogravimetric analysis for the water content of these foods can be advantageous over other methods, because this method does not use toxic and costly reagents solvents and it does not need any sample preparation. Besides, it allows the identification of the range of temperatures at which water is eliminated and it gives information about the stability and degradation profile which can contribute to the optimization of production processes of these foods.