O uso da constante dielétrica para identificação da diluição do leite In Natura

Abstract

In the present work is studied the dielectric constant to identification of water addition in full milk. To achieve this goal, a parallel plate capacitive cell was constructed in stainless steel and an LCR meter was used for capacitance measurement. The milk samples were obtained in the Upaon-Açu Island, in two places. These it were diluted with water of UFMA supply in the proportion known from 15% to 90%. Samples from approximately 120 ml was used. The measurements were realized in the frequency range of 100 Hz and 100 KHz, the voltage used was 1 V. The sample temperature was maintained in approximately 8◦C. The capacitance data were converted in dielectric constant for these it to be used in the course of work. The SSP software version 25.0 was used for the statistical analysis. To the verification of normality of samples was used the Kolmogorov-Smirnov test. The H of Kruskal-Wallis and U of Mann-Whitney test were used for differentiation of groups. The Kolmogorov-Smirnov test showed that the data are not normal. The Kruskal-Wallis test showed that all of the frequencies presented significant differences among the groups, except the frequency of 100 Hz (p=0,06). The 1 kHz and 20 kHz frequencies showed a decrease in the dielectric constant almost linear with addition of water, already in others, this decrease occurred in the softer way, except in 10 kHz that presented a different behavior. The 1 kHz frequency, beyond the characteristic of decrease more linear, it is a frequency that is inside the range indicated that can show milk characteristics. Then, this frequency was chose for be studied more deeply. The Mann-Whitney test showed that only group 1 is not difference of group 0 (p=0,05) in the 1 kHz frequency. This result can have be influenced in the direct way by the temperature during the experiment. The Mann-Whitney test in temperature reveals that the group 1 is significantly different of group 0 (p = 0,002), causing a elevation in the constant dielectric value, leave the value of group 1 very close of group 0. In front of this results, it is concluded that the method is viable since that be realized in controlled temperature. The technique needs improvements and tests in several temperatures, and with others adulterants for that it be known how the dielectric constant modify in different situations.