THE EVALUATION OF DEEP FRYING OIL QUALITY WITH THE SPECTROPHOTOMETRIC METHOD FOR THE RAPID ASSESSMENT OF TOTAL POLAR COMPOUNDS

This study focuses on the evaluation of official methods for determining frying oil quality with the new spectrophotometric method. The performance of these methods was examined by usage intermittent deep fat frying of potato chips in sunflower oil for 40 hr. at five consecutive days (8 hr., daily). Chemical analysis is the most reliable way to measure decomposition compounds in frying oil. With the prolonged frying time the amount of total polar compounds (TPCs) rises steadily. It has been suggested that the determination of TPCs is the most reliable method for the measurement of oil deterioration during deep frying processes. Beside, other oil quality indices during 40 hr. of intermittent deep fat frying were analyzed by the official methods and/or by rapidly spectrophotometric absorbance methods. Principal component analysis and linear regression analysis were used in order to assess the obtained results. The results were used to calibrate this spectrophotometric absorbance method. There was a strong correlation (r = 0.999) between quick spectrophotometric absorbance values and TPCs content in the same set of oil samples. The equation for conversion of the spectrophotometric absorbance values to TPCs content is: Y = -57.0083 + 2.64X + 0.049 X². Consequently, spectrophotometric absorbance method was developed to assess deep fat frying oil quality. This study was conducted to examine the relationship of TPCs contents determined by spectrophotometric method with physical, chemical indices and sensory evaluation. TPCs content was found to be correlated with refractive index (r = 0.950), viscosity (r = 0.989), colour (r = 0.993), acid value (r – 0.899), iodine number (r = 0.947), P-anisidine value (r = 0.987), TBA test (r = 0.875), oxidized fatty acids (OFAs) (r = 0.975). Also, TPCs content was correlated with flavour (r - -0.752), greasiness (r - -0.917), crispy texture (r = -0.559) and overall acceptability (r = -0.649).These results showed that the new spectrophotometric absorbance method of frying oil is a good, rapid, simple, convenient and reliable indicator during deep fat frying of sunflower oil tested.