Applications of infrared spectroscopy for quantitative analysis of volatile and secondary metabolites in plant materials

Volatile chemical compounds responsible for the aroma of plant materials are derived from a number of different biochemical and chemical pathways. These chemical compounds are formed during plant metabolism, processing (i.e. fermentation) and post-harvest storage. Not surprisingly, there are a large number of chemical classes of compounds found in plant materials which are present at varying concentrations (ng L-1 to mg L-1), exhibit different degrees of intensity, and have a broad range of boiling points. For many years, classical separation and chromatographic and spectrometric techniques such as gas chromatography (GC) and liquid chromatography (LC) have been used for the isolation and elucidation of volatile compounds from different plant matrices. Spectroscopic techniques in the infrared (IR) wavelength region of the electromagnetic spectrum have been used in the food industry to monitor and evaluate the composition of foods. In the last 10 years IR spectroscopy became one of the most attractive and used methods for plant analysis. This short review discussed the use, with advantages and limitations, of IR spectroscopy technologies to study volatile compounds and secondary metabolites in plant materials.