Smartphone-based colorimetric study of adulterated tuna samples

•Tuna samples were adulterated with NaNO2 and NaNO3, as well as vegetable extracts.•HPLC-DAD was applied to quantify the amount of NaNO2 and NaNO3 in the samples.•Colorimetric analysis was made using a smartphone and a spectroradiometer.•Beetroot and nitrite were the most effective treatments, maintaining red colour.•Colour allows to objectively discriminate between adulteration methods.