Quantitative analysis of acidity level in virgin coconut oils by Fourier transform infrared spectroscopy and chemometrics

Abstract

The quality of virgin coconut oil (VCO), together with its health functionalities, is directly related to its freshness and to the levels of free fatty acids (FFA). Thus, the goal of this work was to develop a quantitative model based on partial least squares regression (PLSR) to predict FFA levels (%) in VCO. A total of 72 Brazilian commercial samples classified in accordance to their shelf life was analyzed. FFA levels ranged from 0.3 to 2.3%. FTIR (Fourier transform infrared spectroscopy) spectra were recorded within a range of 3100 to 680 cm−1 and submitted to mathematical preprocessing. Quantitative models were developed by partial least squares regression (PLSR). Excellent predictive results were obtained, indicating that the FFA levels in VCO could be accurately quantified by FTIR. The correlation coefficient (R) and the root mean squared error of prediction (RMSEP) were, respectively, as high as 0.994 and as low as 0.07.Practical applications: According to international standards, acid‐base titration is the reference method for the determination of FFA in oils. This method is laborious and time‐consuming, uses toxic and flammable solvents and it is susceptible to error when detecting the color change of the indicator. Some of the advantages of FTIR over the official acid‐base titration method are the short time and simplicity of analysis. Besides that, it is non‐destructive and it does not require hazardous solvents and reagents. The results shown in this study indicate that FTIR spectroscopy and chemometrics can be successfully applied to the quantitative evaluation of FFA in VCO.The quality of virgin coconut oil (VCO), together with its health functionalities, is directly related to its freshness and to the levels of free fatty acids (FFA). Acid‐base titration is the reference method for the determination of FFA in oils. This method is laborious and time‐consuming, uses toxic and flammable solvents and it is susceptible to error when detecting the color change of the indicator. FTIR is a rapid, non‐destructive, and accurate technique that could overcome some of the drawbacks of titration methodologies and could be easily implemented in routine quality control laboratories. The results shown in this study indicate that FTIR spectroscopy and chemometrics can be successfully applied to the quantitative evaluation of FFA in VCO.