A Low-Cost NIR Digital Photometer Based on InGaAs Sensors for the Detection of Milk Adulterations With Water

The adulteration of milk with water is a very common problem, which reduces its nutritional value and industrial yield, and can also represent a major risk of contamination. The standard method for detecting this kind of fraud is the cryoscopy, which fails when the adulteration is done along with other substances. Therefore, there is a need for new and more robust techniques for this purpose. With this goal, we propose a prototype of a digital photometer to quantify water added to milk. This is a microcontrolled, portable device, which uses three LEDs with emission in the near-infrared (IR) region and was developed without the use of lenses, filters, or moving parts. This equipment measures the transmittance of IR radiation through milk samples to assess the addition of water. In this paper, we present the results of experiments that were conducted with diluted milk samples containing 0%-25% of added water, using the proposed equipment and the standard method of cryoscopy. In the measurements of the percentage of added water, the mean absolute error was <;1%. In terms of repeatability, in two sets of ten measurements, we obtained absolute deviations from the average corresponding to less than 0.7% of added water. Results show that the prototype response is similar to the one of a commercial cryoscope but faster.