Milk fat content is a key quality parameter in the dairy industry, directly influencing product value, nutritional properties, and industrial performance. Conventional methods used for fat determination are effective but often require hazardous reagents, multiple processing steps, and specialized laboratory infrastructure. In this context, colorimetric nanosensors based on gold nanoparticles represent a promising alternative, offering simplicity, rapid response, and visual detection capabilities. This study aimed to investigate the colorimetric interactions between gold nanoparticles and the main fatty acids present in bovine milk: palmitic, oleic, and caprylic acids, in order to assess their potential for future milk fat sensing applications. Gold nanoparticles stabilized with citrate and Triton X-100 exhibited distinct colorimetric responses upon interaction with fatty acids. Visual inspection revealed concentration-dependent color changes for all tested fatty acids, with the most pronounced response observed for caprylic acid, characterized by a clear transition from red to blue tones. Image-based RGB analysis, including histogram evaluation and color value calculations, confirmed a non-linear decrease in the red component and an increase in the blue component, particularly at higher concentrations of caprylic acid, where the blue intensity exceeded the red. Palmitic and oleic acids induced more subtle color changes, which became evident mainly at higher concentrations. UV–Vis absorption spectroscopy corroborated the image-based analyses, showing a noticeable plasmon band shift for caprylic acid, while spectral changes for palmitic and oleic acids were limited due to sample turbidity. The results demonstrate that the colorimetric response of gold nanoparticles is strongly influenced by the physicochemical properties of fatty acids, especially carbon chain length and solubility. The combined use of RGB analysis, and UV–Vis spectroscopy proved effective in capturing both subtle and pronounced color changes. These findings highlight the potential of gold nanoparticle-based colorimetric systems as a foundation for the development of a simple, low-cost, and rapid nanosensor for milk fat quantification, offering a promising alternative to conventional analytical methods used in dairy quality control.
Ribeiro et al. (Mon,) studied this question.