Spot Test for Protein Determination in Raw Bovine Milk through Chemical Analysis Combined with Digital Image Processing on a Smartphone
milk; protein; biuret; spot test; smartphone.
Cow's milk is an important natural source of protein in human nutrition. During the production and processing of milk, it is crucial to monitor parameters such as protein content. However, in rural environments, there are significant challenges, such as the lack of adequate laboratory infrastructure and the logistical difficulty of sending samples for analysis in distant locations. The use of smartphones in Spot Tests for chemical analyses via image processing has been explored in colorimetric tests, converting digital images into the concentration of a specific analyte. With a simple interface and effective analytical response, this technology allows real-time testing at the site of interest, aiding decision-making. This work proposes the development of a smartphone-based colorimetric spot test, based on the biuret reaction, to measure the protein content in raw bovine milk. In the biuret reaction, the peptide bonds present in proteins (-CO-NH-) interact with copper ions (Cu²⁺) in an alkaline solution, resulting in the formation of a coordination complex that exhibits a violet color, directly proportional to the protein concentration. To optimize the method, a kinetic study of the biuret reaction, 2³ factorial design with a central point in RGB image capture conditions, and linear regression will be conducted. For validation, figures of merit such as linearity, precision, limit of quantification, limit of detection, and robustness will be determined. A colorimetry software will be developed in Python® for both Smartphone and Desktop. A comparative study of the Spot Test results will also be carried out against responses obtained from other milk analysis equipment, such as Fourier Transform Spectroscopy and Ultrasound. Upon completion, the developed Spot Test will consist of a smartphone application, biuret reagent, and the reaction chamber, which will allow image capture for processing by the software and obtaining protein content results in milk.