Salak fruit (Salacca zalacca), commonly known as snake fruit, is used indigenously as food and for medicinal applications in Southeast Asia. This study was conducted to evaluate the α-glucosidase inhibitory activity of salak fruit extracts in correlation to its Fourier transform infrared spectroscopy (FT-IR) fingerprint, utilizing orthogonal partial least square. This calibration model was applied to develop a rapid analytical method tool for quality control of this fruit. A total of 36 extracts prepared with different solvent ratios of ethanol⁻water (100, 80, 60, 40.20, 0% v/v) and their α-glucosidase inhibitory activities determined. The FT-IR spectra of ethanol⁻water extracts measured in the region of 400 and 4000 cm−1 at a resolution of 4 cm−1. Multivariate analysis with a combination of orthogonal partial least-squares (OPLS) algorithm was used to correlate the bioactivity of the samples with the FT-IR spectral data. The OPLS biplot model identified several functional groups (C⁻H, C=O, C⁻N, N⁻H, C⁻O, and C=C) which actively induced α-glucosidase inhibitory activity.
Fruit of salak (Salacca zalacca) is traditionally used and commercialized as an antidiabetic agent. However, the scientific evidence to prove this traditional use is lacking. This research was aimed to evaluate the metabolic changes of obese-diabetic (OBDC) rats treated with S. zalacca fruit extract using proton-nuclear magnetic resonance (1H NMR)-based metabolomics approach. This research presents the first report on the in vitro antidiabetic effect of S. zalacca fruits extract using this approach. The obtained results indicated that the administration of 400 mg/kg bw of 60% ethanolic S. zalacca extract for 6 weeks significantly decreased the blood glucose level and normalized the blood lipid profile of the OBDC rats. The potential biomarkers in urine were 2-oxoglutarate, alanine, leucine, succinate 3-hydroxybutyrate, taurine, betaine, allantoin, acetate, dimethylamine, creatine, creatinine, glucose, phenyl-acetylglycine, and hippurate. Based on the data obtained, the 60% ethanolic extract could not fully improved the metabolic complications of diabetic rats. The extract of S. zalacca fruit was able to decrease the ketones bodies as 3-hydroxybutyrate and acetoacetate. It also improved energy metabolism, involving glucose, acetate, lactate, 2-hydroxybutyrate, 2-oxoglutarate, citrate, and succinate. Moreover, it decreased metabolites from gut microflora, including choline. This extract had significant effect on amino acid metabolism, metabolites from gut microflora, bile acid metabolism and creatine. The result can further support the traditional claims of S. zalacca fruits in management of diabetes. This finding might be valuable in understanding the molecular mechanism and pharmacological properties of this medicinal plant for managing diabetes mellitus.