Colorimetric paper-based detection of phosphoric acid in packaged foods for point-of-care quality control

Here, we present the development of a paper-based colorimetric device for the rapid and easy quantification of phosphoric acid (PA) in packaged food samples using the phosphoantimonylmolybdenum (PMB) assay. The underlying sensing mechanism is based on the molybdenum blue reaction, in which phosphate reacts with a molybdate-antimony complex under acidic conditions and is subsequently reduced by L-ascorbic acid to develop a blue color which is quantified using smartphone imaging. The developed platform enables accurate PA determination with a LoD of 22 ppm and LoQ of 73 ppm and shows strong agreement with standard spectrophotometric results. We have evaluated 24 commercially available packaged foods spanning liquid, semi-solid, and solid matrices, requiring minimal sample preparation steps. A systematic investigation of sample-related effects revealed that strongly acidic foods frequently exhibit deviations greater than 10% relative to spectrophotometry; however, this behavior cannot be generalized and is further influenced by food colorants and matrix constituents. To quantify matrix interference, gelatin-based surrogate matrices were examined, which consistently produced higher responses on the paper platform compared with spectrophotometric analysis, affirming the significant role of the matrix. Furthermore, our on-site testing outside the laboratory settings indicates the development of an accessible and affordable tool for point-of-care settings for food quality control without necessitating sophisticated infrastructure.