## 1 Introduction  
The Brazilian dairy production chain sells more than 25.01 billion litres per year through its 1,171,190 dairy farms [1], and it generated revenues of BRL 70.2 billion for the country's dairy industry in 2017, a 4% increase over 2016 [2]. Among the most consumed products are long-life milk, commonly known as UHT (ultra-high temperature), reaching 7.026 billion litres in 2017, 2.8% more than in 2016. According to the Brazilian Long-Life Milk Association (ABVI), this growth was mainly due to low consumer prices throughout the year and a continuous increase in its share of the total volume of drinking milk [2]. In addition to these factors, the preference for long-life milk consumption by about 80% of the population is due to its practicality in storage without the need for refrigeration and extended shelf life [3, 4]. We must consider that the thermal process of ultra-pasteurisation maintains the nutritional and organoleptic characteristics of fresh milk [5] and, according to [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] (2014), does not significantly alter the physical and chemical properties of the milk. However, it is not only the nutritional qualities that define a good-quality food. The physical and chemical characteristics of milk can be altered due to the biological and environmental conditions of the cows, such as the breed, feeding (nutrition plan and physical form of the feed), ambient temperature, management and the interval between milking, milk production and infection of the mammary gland ([PERSON], 2015), and fraud in the processes of obtaining, storing, transporting, and processing milk ([PERSON], 2015). The relationship between milk components is stable and this condition is the basis for tests aimed at pointing out the occurrence of problems that alter its composition ([PERSON], 2015). The most common adulterants in milk are water, whey, colostrum, amylaceous substances, gum, sucrose, salt and other kinds of milk ([PERSON], 2015). To prevent fraud and maintain the quality of milk and its derivatives in Brazil, MAPA's Normative Instruction No. 30/2018 makes official the Manual of Official Methods for Analysis of Food of Animal Origin ([PERSON], 2015) ([PERSON], 2015), the adulteration of milk by adding water may harm the health of the consumer, since the quality of this diluent is unknown, in addition to reducing the nutritional value of its components. The results of the above-mentioned author, based on the physical quantities of density and specific heat, which generate the volumetric thermal capacity, made it possible to quantify the percentage of added water in the samples compared to the reference methods (cryoscopy and density) up to an adulteration of 10%. Frequently, routine official analyses are not always efficient in detecting irregularities when they are performed with small additions of adulterants ([PERSON], 2015). Some of the techniques provided by legislation for evaluating milk quality, such as freezing point (cryoscopy) ([PERSON], 2015) and density, can be falsified by the simultaneous addition of water and restorers like sodium chloride and ethanol ([PERSON], 2015). Substances like sodium bicarbonate, for example, can be used to restore acidity, thereby masking reference techniques such as the Dornic method ([PERSON], 2015). Detecting the most common frauds involves the use of sophisticated techniques such as spectroscopy, gel electrophoresis, absorption spectroscopy, and liquid chromatography ([PERSON], 2015), and for this reason the scientific community is seeking new alternatives, preferably faster and cheaper, such as electrical bioimpedance ([PERSON], 2015; [PERSON], 2015; [PERSON], 2015) and the method of wave propagation through the material using piezoelectric diaphraggrams ([PERSON], 2015). Electrical bioimpedance presents an alternative for detecting and monitoring biological parameters and processes, with the advantage of being relatively inexpensive ([PERSON], 2015) and non-invasive ([PERSON], 2015; [PERSON], 2015).