Rancidity is immediately noticeable by smell or taste...no sophisticated test required. TOTOX levels are often quoted as an indicator of marine oil freshness, but oxidative values are only one set of parameters in determining the quality or rancidity of marine oil. (Marine oils with high oxidative values will likely have strong odor and poor taste, but so can marine oils with low values.) Metagenics marine oils are tested for peroxide and anisidine levels (which may be used to calculate TOTOX) after manufacture of the oil, prior to adding flavor and/or encapsulation. For added insurance, Metagenics also repeats peroxide assays after final processing to validate that no oxidation occurred during manufacture to degrade oil quality. Natural antioxidants are also added to maintain stability over the product's shelf life.