Desenvolvimento de microdispositivo a base de papel para avaliação da acidez do leite

Abstract

Milk is a product of great nutritional value and economic relevance. Its acidity is one of the essential parameters for verifying the hygienic-sanitary quality, presenting normally with pH = 6.6 - 6.8. Variations in this parameter may indicate the presence of: colostrum; mastitis; neutralizing; excess of microorganisms, making their processing unfeasible. Due to the importance of this parameter, it is important to develop inexpensive, faster and easy-to-interpret methods that enable initial screening of this input. The use of paper-based microdevices has advantages such as low cost, ease of use and portability, making them promising the evaluation of this parameter. This work aims to develop a paper-based analytical microfluidic device for colorimetric evaluation of milk acidity. The device was elaborated through the integration of filter paper and adhesive tapes. A paper cutter was used to obtain devices with diameter of 0.5 cm. To evaluate the efficiency of the proposed microdevice, two supports of the base material (adhesive tape and plastic) and the addition of different volumes of indicator solution (5, 10, 15 and 20 μL) were evaluated. A commercial alizarol solution (72 ° GL) was used as a colorimetric indicator, which was added to the device, dried at room temperature and then the sample was added in the same volume. For quantitative evaluation of the analyte, an analytical curve was performed with the following pH values: 6.0; 6.4; 6.6; 6.8 and 7.0, obtained by adding HCl 0.1 mol L-1 and NaOH 0.1 mol L-1 solutions in a commercial milk sample and monitoring in a properly calibrated pH meter. The images capture and data evaluation were performed in two ways: using a smartphone camera in an ABS box associated with the PhotoMetrix Pro® software; and using a Samsung Xpress scanner, image processing using CorelDRAW 2018 software and data analysis using OriginPro 9.0 software. Using the plastic support, it was possible to add an indicator solution and a milk sample without leaks, generating a product with an innovative and effective design. The use of 5 μL of the indicator solution made it possible to fill the entire device and allowed colorimetric evaluation. The device allowed a qualitative assessment of the acidity of the milk by varying the colors: yellow - acidic pH; light orange - optimum pH; and lilac - basic pH. Quantitative evaluation of the triplicate analysis was possible, obtaining a linear correlation coefficient of 0.99737, demonstrating the potential of the method developed at low cost as an alternative to conventional methods.