Partial least squares correlation analysis of ethanol and ethanoic acid in vinegar using attenuated total reflectance-fourier transform infrared spectroscopy

Abstract

Vinegar is a common material that is use in our daily life as it has vast usage, from being used in cooking and salad dressing, up to as cleaning substance due to its acidity behavior. Vinegar is made from different types of sources such as wine, apple, rice and others by fermentation of ethanol into ethanoic acid. Wine being the source of vinegar cause doubts in consumer when buying it in the market especially Muslims. According to Malaysian Food Act 1983, it is said that the content of acetic acid in any vinegar must not be more than 12.5 % w/v. In this study, Attenuated Total Reflectance-Fourier Transform Infrared Reflectance (ATR-FTIR) technique and Partial Least Squares Regression (PLS) method was used to build a model to quantify ethanol and ethanoic acid in standard samples and apply it to four commercialized vinegar. The standard samples are from 10 % v/v to 90 % v/v with 20 % v/v interval. Another four commercialized vinegar was used as real samples. Therefore, there are a total of 22 samples were scanned using ATR-FTIR and the absorbance values were recorded from 650 to 4000 cm^-1. The digitized spectra were saved in Microsoft Excel and later imported to MATLAB for further analysis. Then the spectrophotometric data were analyzed for PLS Regression. Each spectrum data was selected every 1cm^-1 interval and data at Y-column 1592 which is 818 cm^-1 was chosen as it gives the best result when building model. The model obtained shows the model can be accepted as the value of R² is 0.996, Root Mean Square Error of Calibration (RMSEC) of 0.0005535, Root Mean Square Error of Cross-Validation (RMSECV) of 0.0011474 before data of real samples were applied. After data of real samples were applied into this model, the R²  obtained maintained high which is 0.999, while the values of Root Mean Square Error of Prediction (RMSEP) is 0.00040802 which is very small.