Halal Authentication of Fatty Acids in Bar Soap Products Utilizing GC-MS and FTIR Spectroscopy in Conjunction with Chemometrics

Bar soap is a cleansing product made through the saponification reaction between alkali and fatty acids derived from animal or plant sources. For Muslim consumers, the halal status of soap is an important concern because certain manufacturers may use porcine fat as a raw material in soap production. This study aimed to authenticate the sources of fatty acids in bar soap by analyzing the profiles of bovine fat, porcine fat, and commercial bar soap samples using a combination of gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared (FTIR) spectroscopy, and chemometric analysis. For the method, beef tallow and lard were extracted using the dry rendering method and then processed into reference soap samples, while six commercial bar soap products collected from the market were also analyzed for comparison. Fatty acid components were identified by GC-MS based on chromatographic peaks and mass spectral data, while FTIR spectra were recorded in the range of 4000 to 400 cm⁻¹ and further evaluated using chemometric techniques. The results showed that beef tallow-based soap was mainly characterized by stearic acid (45.45%) and palmitic acid (28.78%), whereas lard-based soap contained a higher proportion of oleic acid (37.58%) and a much lower level of stearic acid (0.54%). FTIR combined with chemometrics analysis in the 1200–800 cm⁻¹ region successfully differentiated beef tallow-based soap, lard-based soap, and commercial bar soap samples. Consequently, the integration of GC-MS, FTIR, and chemometrics was effective for the halal authentication of bar soap, and none of the commercial samples showed evidence of porcine fat.