Determination of the Sum of Dimer and Polymer Triglycerides and of Acid Value of Used Frying Fats and Oils by Near Infrared Reflectance Spectroscopy

Abstract

Abstract Near infrared reflectance spectroscopy (NIRS) in the transaction mode was applied to determine the sum of dimer and polymer triglycerides (DPTG) contents and acid value of used frying fats and oils. A filter instrument and a calibration sample set were used to determine DPTG content and acid value. For each parameter, a 7-wavelength calibration was developed using multiple linear regression analysis. For a validation set comprising 44 samples for the NIRS-DPTG determination in the range of 2.2 to 32.7% m/m, the correlation coefficient between NIRS and liquid chromatography (LC) was 0.976, with a standard error of prediction (SEP) of 1.8% m/m. For a validation set comprising 36 samples for the NIRS-acid value determination in the range of 0.30 to 18.8 mg potassium hydroxide per gram of sample (mg KOH/g), the correlation coefficient between NIRS and titration was 0.996, with a SEP of 0.33 mg KOH/g. Validation after routine operation for 1 year provided SEPs of 2.3% m/m and 0.44 mg KOH/g for DPTG and acid value determination, respectively. NIRS screening of 1400 samples collected during 1992 precluded the need for 1149 DPTG determinations by LC (82.1%) and 1033 acid value determinations by titration (73.8%), which are methods the judicature in The Netherlands accepted, because those samples appeared to comply with legislation.