This assay at Brunswick Labs utilizes a pH differential method. It is based on the fact that anthocyanin pigments reversibly change color with a change in pH; the colored oxonium form exists at pH 1.0, and the colorless hemiketal form predominates at pH 4.5. The difference in the absorbance of the pigments at 520 nm is proportional to the pigment concentration. Results are expressed on a cyanidin-3-glucoside basis. Although determination of total anthocyanin pigment is useful in assessing the quality of food products, it is highly recommended to be used in conjunction with analyses for individual anthocyanins.