A rapid colorimetric method for the quality determination of cooking oils

A rapid colorimetric method for the quality determination of cooking oils was established on the basis of a synthesized nano gold probe which was modified by poly(diallyl dimethylammonium) chloride(PDDA) and cricoid dextrin(alpha,beta,gamma,or mixed) at the same time. When the solution of nano gold prboe was mixed with illegal cooking oil at the same volume,a selective non-covalent interaction was observed between the probe solution and the free fatty acid,hydrogen peroxide,aldehyde,ketone and other impurities in the inferior oil,which incured nano gold probe transfer from water phase to the upper oil phase and led to a color change. The degree of color change was proportional to the content of inferior oil,the oil quality could be qualitatively detected through color change and stratified situation and quantitatively detected according to the wavelength of 630 nm in UV-visible absorption spectrum. The results showed that qualified cooking oil mixed with 3.0% of the illegal cooking oil could be detected,and more than 5.0% of the illegal cooking oil could be detected accurately by naked-eye. The methods indicated that the accurate rates were 97% when applied in blind test samples. This work would be helpful for the rapid and on-site detection of illegal cooking oils.