FTIR spectral correlation with alpha-glucosidase inhibitory activities of selected leafy plants extracts

Abstract

Fourier transform infrared spectroscopy (FTIR) is a simple, rapid analytical technique used for the identification of organic functional groups of biomolecules. This study aimed to investigate the use of FTIR spectroscopy method for rapid detection of the α-glucosidase inhibitory activity of crude extracts of edible leafy plants, characterization of functional groups of chemical components present in crude extracts, and identification of possible biomolecules responsible for α-glucosidase inhibitory activity. Powdered leaves of five different plants, namely Le-kola pala (LE) (Premna procumbens), Kora kaha (KK) (Memecylon umbellatum), Koppa (KO) (Polyscias scutellaria), Stevia (ST) (Stevia rebaudiana), and Yaki naran (YK) (Atlantia ceylanica) were sequentially extracted with hexane, ethyl acetate (EtOAc) and methanol (MeOH). The FTIR spectra of crude plant extracts were obtained following the KBr pellet method, within the range of 4000-500 cm-1. The plant extracts were subjected to assay the α-glucosidase inhibitory activity. Further, the multivariate predictive models for α-glucosidase inhibitory activity were developed using partial least square (PLS) regression analysis. The highest Rc2 (0.96), Rcv2 (0.87), Rp2 (0.93), and the lowest RMSEC (24.10), RMSECV (41.70), and RMSEP (81.04) values were noticed for spectral region range from 1700 cm-1 to 1800 cm-1, indicating the strongest correlation to the α-glucosidase inhibitory activity, while the spectral region range from 1500 cm-1 to 1700 cm-1 was found to have the lowest Rc2 (0.71), Rcv2 (0.52), Rp2 (0.45) and the highest RMSEC (61.14) and RMSECV (80.21), indicating the lowest correlation to the α-glucosidase inhibitory activity. As the peak appearing in the range of 1700-1800 cm-1 is usually ascribed to C=O stretching vibration of ester groups, ketones, and carboxylic acids, there was a strong correlation between α-glucosidase inhibitory activity with those organic functional groups. The present study suggests that FTIR spectral analysis together with PLS regression analysis would be a convenient, rapid tool to determine α-glucosidase inhibitory activity of plant extracts.