Food analysis is essential for ensuring food quality and safety, with protein content being one of the most relevant compositional parameters from both nutritional and technological perspectives. Although the Kjeldahl method is the reference technique for protein quantitation, reversed-phase high-performance liquid chromatography (RP-HPLC) provides high specificity for individual proteins and was used in this study as an independent comparative method. Unlike nitrogen-based methods, RP-HPLC enables direct quantitation of defined protein standards. This work proposes the determination of protein concentration using the Bradford assay combined with digital image analysis (DIA), replacing conventional spectrophotometric detection. A glass slide was evaluated as a sample support, requiring only 14 µL of sample, substantially less than conventional microplates. Images were acquired with a smartphone, and the complete analytical workflow, from image acquisition to protein concentration calculation, was semi-automated using MATLAB software. The method was evaluated using bovine serum albumin (BSA) and casein standards and applied to food samples. Protein concentrations obtained by the Bradford-DIA method showed good agreement with RP-HPLC, with errors ranging from 1.7% to 17% for standards and from 1.1% to 23% compared with labelled protein values. The proposed approach provides a rapid, low-cost, and miniaturised alternative for protein determination.

A green digital image photometry method for the quantification of niacinamide in commercial cosmetic serums and creams is described. The method is based on the formation of an orange complex between niacinamide and iron (III) chloride in microplates under LED backlighting. The analytical signal was defined as (255 - B), where B corresponds to the blue channel intensity in the RGB colour model. Calibration was performed using microplate-based standards, and the method was applied to commercial cosmetic samples. Relative errors compared to HPLC-DAD were lower than 10.0%, and an elliptical joint confidence region test indicated no significant differences between slopes and intercepts and the ideal values of 1 and 0 at the 95% confidence level. Paired Student's t-test and F-test confirmed no significant differences in agreement and precision between methods. Deviations from labelled concentrations were generally below 6.0%, with a maximum value of 14.0%. Precision, evaluated over two months, showed relative standard deviations below 9.0%. Recovery values ranged from 84 to 114%. UV-Vis spectrophotometry was used to support the validation of the colorimetric response of the niacinamide-FeCl₃ system. The proposed approach was applied to rapid screening of niacinamide in cosmetic products and compared with a reference HPLC-DAD method.