Direct measurement of conjugated linoleic acid (CLA) in CLA-rich soybean oil by ATR-FTIR spectroscopy

CLA-rich soy oil (∼22%) has been produced by photo-isomerization of oil by UV radiation. The CLA isomers in oils are measured as fatty acid methyl esters by a gas chromatography--flame ionization detector (GC--FID) technique, which requires approximately 2 h to complete the analysis. Potato chips have been produced as a dietary vehicle for the oil. The CLA analysis in potato chips involves analysis of the extracted oil which makes the process time consuming. Hence, we aim to develop separate methods for rapid determination of CLA isomers in CLA-rich soy oil and potato chips. For the development of model for oil, soy oil with 0.38--25.11% total CLA was obtained by photo-isomerization of 96 soy oil samples for 24 h. A sample was withdrawn at 30 min intervals with repeated processing using a second batch of oil. Six replicates of GC--FID fatty acid analysis were conducted for each oil sample. The spectrum of oil samples was collected by ATR-FTIR. The samples for development of the method for potato chips were obtained by frying potato slices in 300 g CLA rich soy oil dilutions containing CLA levels ranging from 0 to 25% at 175°C for approximately 3 min. Duplicate GC-FID fatty acid analysis were conducted on oil extracted from each batch of potato chips. The chips were ground and scanned using ATR-FTIR spectroscopy with a high pressure clamp. Calibration models for both the experiments were developed using PLS regression by Unscrambler 9.8. Models were validated using a full cross-validation technique and tested using unknown samples. The models that were developed for oil had cross-validated coefficients of determinations (R2v) between 0.97-0.99 with RMSEV values ranging from 0.07-1.14% CLA while those for potato chip samples ranged between 0.96 and 0.91 and 1.44-0.005% CLA respectively. The methods developed provided CLA rapid analysis in oil and potato chip samples.