A new spectrophotometric method for the rapid assessment of deep frying oil quality

A new and quick spectrophotometric method was developed to assess deep-frying oil quality. The scanned spectrophotometric curves of the frying oil samples from 350 and 650 nm wavelength changed systematically with the duration of deep frying. The absorbances of the frying oil samples, especially those measured at 490 nm, increased significantly during frying and were significantly correlated to frying time (I greater than or equal to 0.95, P < 0.001). There was a strong correlation between the absorbances of a set of oil samples taken from 0 to 80 h of deep frying and total polar compound contents in the same set of oil samples analyzed using the American Oil Chemists' Society official method (r = 0.924, P < 0.001). The equation for conversion of the absorbances to total polar compound contents is y = -2.7865x(2) + 23.782x + 1.0309. The absorbances of 10 different types of frying oils with samples taken from 0 to 80 h of deep frying in duplicate were also strongly correlated to total polar compounds in the same oil samples (r = 0.953, P < 0.001, n = 220). The results show that this method is fast, simple, convenient, and reliable.