Quality assessment of frying oil using short-chain fatty acid profile and infrared spectrum coupled with partial least squares

The deterioration of soybean oil (SO), palm oil (PO), and rapeseed oil (RO) for deep-fat frying chicken breast meat (CBM) and potato chips (PCs) was evaluated based upon their short-chain fatty acids (SCFAs) profiles as well as free fatty acid (FFA) content, carbonyl value (CV), and total polar compounds (TPC) content. In addition, Fourier-transform infrared (FTIR) spectra of oils combined with partial least squares were applied to predict the FFA content, CV, and TPC content in oils. Results showed that the formation of SCFAs was accompanied the reduction of unsaturated fatty acids during 12 h/day for 3 days. For frying PCs with SO, the heptanoic acid (C7:0) continuously increased from 0.01 to 0.15 g/kg and octanoic acid (C8:0) increased from 0.008 to 0.65 g/kg, while the contents of linoleic and linolenic acids reduced from 45.69-41.43 to 4.03-3.20%, respectively. For frying CBM with RO, the contents of C7:0, C8:0, and nonanoic acid were in ranges of 0.05-0.38, 0.03-1.19, and 0.11-0.17 g/kg, while contents of linoleic and linolenic acids reduced from 22.15-18.89 to 7.83-6.21%, respectively. The FFA content, CV, and TPC content in oils predicted by the constructed linear regression model were in ranges of 0.21-2.61 KOH g/kg, 9.76-58.98 meq/kg, and 8.02-36.91%, respectively. The root mean standard error of prediction, coefficient of determination (R-2) for the validation set, and ratio of prediction to deviation for all validation analyses were in ranges of 0.2127-6.7364, 0.8717-0.9608, and 1.1548-4.2984, respectively. A logistically positive relationship (R-2 = 0.7982-0.9700) between the content of C8:0 and CV or TPC content was found in frying oils used for frying both CBM and PCs. Thus, both the measurement of SCFAs and FTIR analysis could be used to efficiently monitor the deterioration of frying oils during deep-fat frying.