LAUSR

This article describes the development of a new tool for interpreting the thermal stability of raw milk by means of the alizarol test, using a multivariate calibration model on a mobile device. The alizarol test is a semiquantitative test that uses an alcoholic solution containing a pH indicator (alizarin). Color judgment and correlation with pH are done visually and may involve several errors and differences between one analyst and another. Therefore, a pH scale (3 to 12) was constructed with raw milk for the alizarol test using a mobile device for image acquisition for each pH point (in triplicate). For quantitative pH determination, a new version of the PhotoMetrix® app was developed (named PhotoMetrix Pro®), including partial least square (PLS) regression tools, choosing RGB histograms and mean center preprocessing. The alizarol stability test was performed using 2 mL of sample and 2 mL of alizarol. To verify the performance of the PLS model, seven samples from different milk producers were analyzed. The results indicate that the root mean square error of calibration (RMSEC) was 0.25, and the root mean square error of prediction (RMSEP) was 0.30, very satisfactory. The results obtained by the proposed method were compared to those obtained using the potentiometric method (reference method); agreement between 95.0 and 100.9% was obtained, without statistical difference (p > 0.05). This application using PhotoMetrix Pro® could be an alternative for fast and reliable interpretation of the alizarol test.