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A simple and rapid Fourier Transform infrared (FTIR) spectroscopy method was developed to determine the main essential oil components (carvacrol, thymol and p-cymene) in the antimicrobial LDPE films incorporated with oregano (Origanum vulgare) and thyme (Thymus vulgaris) essential oils. The ATR-FTIR spectrum of pure active components (carvacrol, thymol and p-cymene) was characterized, and the ranges between 1125 cm-1 - 1095 cm-1, 1170 cm-1 - 1140 cm-1 and 1050 cm-1 - 1017 cm-1 were respectively used for quantitative estimation. Partial least square (PLS) analysis was used for quantitative analysis. FTIR spectroscopy with chemometrics, using the PLS-1st derivative spectra, could predict the content of active compounds accurate to an r2 greater than 0.99 and a standard error of prediction (SEP) less than 0.7. The developed method was successfully applied to predict the concentration of active compounds: carvacrol, thymol and p-cymene in oregano and thyme essential oils with results compared to those of the GC-MS method. The described non-destructive method can be applied in the industry instead of extraction, distillation and blend processes of the mentioned essential oils and can be extended to detect the content of carvacrol, thymol and p-cymene in active packaging and other commercial products.
Valderrama et al. (Sun,) studied this question.