Application of infrared spectroscopy using Fourier transformation in the analysis of bioactive compounds of citrus fruits - systematic review

Citrus fruits (Citrus spp.) constitute a significant portion of global agricultural production due to their rich nutritional profile and the presence of bioactive compounds with positive health effects. Phytochemicals such as flavonoids, carotenoids, phenolic acids and terpenoids contribute to the antioxidant, anti-inflammatory and cardioprotective effects of citrus fruits and make them important and functional foodstuffs. Infrared spectroscopy coupled with Fourier transformation, or FTIR spectroscopy, is increasingly used as a rapid, non-destructive, and reliable method for analysing the chemical composition of fresh and processed citrus fruit samples, including juices, pulp, peel, and essential oils. FTIR enables the identification and quantification of bioactive substances by detecting characteristic vibrational bands. In combination with chemometric techniques such as principal component analysis (PCA) and the method of partial least squares regression (PLSR), it allows for the accurate classification and estimation of the content of bioactive compounds. The method has also proven useful for authentication, quality control, and the analysis of citrus waste and by-products. Despite its many advantages, FTIR spectroscopy has limitations in the analysis of complex mixtures and low concentrations of compounds, as well as poor selectivity compared to methods such as high-performance liquid chromatography (HPLC) or gas chromatography with mass spectrometry (GC–MS). Therefore, it is often used in combination with other techniques to increase analytical accuracy and specificity. Thanks to its simplicity, speed, and ability to analyse different matrices, FTIR spectroscopy is a valuable tool in food and agricultural science, especially in the context of quality control and valorisation of bioactive compounds in citrus fruits.